Crpentary+Fitting

Forging 271

Hand hammersThere are two major kinds of hammers are used in hand forging: (1) the hand hammer

used by the smith himself and (2) the sledge hammer used by the striker. Hand hammers(Fig. 14.8) may further be classified as (a) ball peen hammer, (b) straight peen hammer, and(c) cross peen hammer. Sledge hammers (Fig. 14.8) may further be classified as (a) Doubleface hammer, (b) straight peen hammer, and (c) cross peen hammer. Hammer heads are madeof cast steel and, their ends are hardened and tempered. The striking face is made slightlyconvex. The weight of a hand hammer varies from about 0.5 to 2 kg where as the weight ofa sledge hammer varies from 4 to 10 kg.

Eye

(a ) Doub le face

Straigh t peen

Face

Cross peen

(b ) S traigh t peen (c) C ross peen

Ba ll peen ham m er

Straigh t peen ham mer

Cross peen ham mer

Fig. 14.8 Types of hammers

Set hammerA set hammer generally used in forging shop is

shown in Fig. 14.9. It is used for finishing corners inshouldered work where the flatter would beinconvenient. It is also used for drawing out the gorgingjob.

Face

Eye

Hand le

Fig. 14.9 Set hammer

364 Introduction to Basic Manufacturing Processes and Workshop Technology

364

FITTING

19.1 INTRODUCTION

These days small, medium and heavy industries are using automatic machines. Butbench and fitting work also plays a significant role for completing and finishing a job to thedesired accuracy. Most of semi-finished works can be accomplished with fairly good degree ofaccuracy in a reasonable time through various kinds of quick machining operations. They stillrequire some minor operations to be performed to finish the job by hand. The term benchwork denotes the production of an article by hand on the bench. Where as fitting is theassembling of parts together and removing metals to secure the necessary fit, and may ormay not be carried out at the bench. These two types of work require the use of a largenumber of hand tools and other devices or equipments that involve a number of operationsfor accomplishing the work to the desired shape and size. Some of the commonly used toolsare discussed as under.

19.2 TOOLS USED IN FITTING SHOP

Tools used in bench and fitting shop are classified as under.

1. Marking tools

2. Measuring devices

3. Measuring instruments

4. Supporting tools

5. Holding tools

6. Striking tools

7. Cutting tools

8. Tightening tools, and

9. Miscellaneous tools

The above mentioned tools are further classified and discussed as under.

1. Markeing ToolsThese are sub classified as steel rule, circumference rule, straight edge, flat steel square,

19CHAPTER

Fitting 365

scriber, semi-circular protractor, divider, trammel, prick punch, centre punch, try square,bevel square, vernier protractor, combination set and surface gauge.

2. Measuring DevicesCommonly used measuring devices and instruments used in bench and fitting shop are

fillet and radius gauge, screw pitch gauge, surface plate, try square, dial gauge, feeler gauge,plate gauge and wire gauge.

3. Measuring InstrumentsLine measuring and end measuring devices. While using line measuring device, the

ends of a dimension being measured are aligned with the graduations of the scale from whichthe length is read directly such as scales or steel rules. Whereas, with end measuring device,the measurement is taken between two ends as in a micrometer, vernier calipers and gaugeblock, etc. End measuring devices are commonly used for measuring accurate and precisiondimensions of components. Some measuring instruments are employed for measuring lineardimensions and others are suitable for determining angular or geometric dimensions. Fewmeasuring instruments are also kept for reference purposes as standards of comparison. Themain measuring instruments are listed as under.

(i) Linear measurements

(A) Non-precision instruments

1. Steel rule

2. Calipers

3. Dividers

4. Telescopic gauge

5. Depth gauge

(B) Precision instruments

1. Micrometers

2. Vernier calipers

3. Vernier depth gauges

4. Vernier height gauges

5. Slip gauges

(C) Comparators

(D) Coordinate measuring machines

(ii) Angular measurements

(A) Non-precision instruments

1. Protector

2. Engineers square

3. Adjustable bevel

4. Combination set


(B) Precision instruments1. Bevel protector5. Angle gauges6. Sine bar7. Clinometers8. Autocollimators9. Sprit level

(iii) Surface measurement1. Straight edge2. Surface gauge3. Surface table4. Optical flat5. Profilo-meter

4. Supporting ToolsThese are vee-block, marking table, surface plate, and angle plate.

5. Holding ToolsThese are vices and clamps. Various types of vices are used for different purposes. They

include hand vice, bench vice, leg vice, pipe vice, and pin vice. The clamps are also of differenttypes such as c or g clamp, plane slot, goose neck, double end finger, u-clamp, parallel jaw,and clamping block.

6. Strking ToolsThese are various types of hammers such as ball peen hammer; straight peen hammer;

cross-peen hammer; double face hammer; soft face hammer.

7. Cutting ToolsThese involve various types of files, scrapers, chisels, drills, reamers, taps, snip or shear

and hacksaws.

Files. There are different types of files such as flat, square, round, triangular, knife,pillar, needle and mill.

Scrapers. These are flat, hook, triangular, half round types.

Chisels. There are different types of chisels used in fitting work such as flat chisel, crosscut chisel, diamond point chisel, half round chisel, cow mouth chisel and side cutting chisel.

The other cutting tools are drills, reamers, taps, snips, hacksaws (hand hacksaw andpower hacksaw) etc.

8. Tightening ToolsThese are pliers and wrenches, which are sub classified as under.

Pliers. These are namely ordinary, needle nose, and special type.

Wrench. These are open single ended, open double ended, closed ended adjustable, ringspanner, offset socket, t- socket, box wrench, pipe wrench and allen wrench.

Fitting 367

9. Miscellaneous ToolsThese are die, drifts, counter sink tools, counter boring tools, spot facing bit and drill press.

Some of above mentioned important tools are discussed as under.

19.2.1 Measuring Tools

19.2.1.1 Steel Rule

Steel rule is generally employed for purpose of measuring rough dimensions and layingout them. It is always advisable to start measuring from 1 cm mark because the end of therule is generally worn out

19.2.1.2 Circumference Rule

It is commonly used for measuring or laying out or as a straight edge. The specialty inthis rule is that the circumference can be taken directly, below the diameter dimension.

19.2.1.3 Straight Edges

There are two types of straight edges namely four edge type (Fig. 19.1(a)) and bridge type(Fig. 19.1(b)) which are made of carbon tool steel and alloy steel. They are generally flatgraduated bar of steel with one longitudinal edge beveled. Straight edges come in variouslengths commonly varying from 2.5 mm up to one meter and above. They are mostly usedfor scribing long straight lines.

Four edges type (a)

Bridge type

(b)

Fig. 19.1 Straight edges

19.2.1.4 Flat Steel Squrae

It is a piece of flat hardened steel with graduations on either end. It is commonly usedfor marking lines in the perpendicular direction to any base line.

19.2.1.5 Scribers

Fig. 19.2 shows the various types of scribers, which are sometimes called the metalworker’s pencil. These are made up of high carbon steel and are hardened from the front edge.Scriber is used for scratching lines on the sheet metal during the process of laying out a job.

Fig. 19.2 Scribers


19.2.1.6 Bever Protractor

The bevel protector (Fig. 19.3) is an instrument used for testing and measuring angleswithin the limits of five minutes accuracy. The common components of this instrument arebase, disc which is fitted with a pivot at the centre and carries a datum line. On this pivotof the protector, the dial is allowed to rotate when the clamping nut is released. The otherunit clamps the blade rigidly to the dial. The blade can be moved lengthwise. Vernier scaleis also provided on the disc to take reading for accurate measurement. Dial is graduated indegrees over an arc.

Fine adjustm ent nut & screw

M ain scale

Pro tractor

Edge bar

Sector

Square

Slid ing b lade

Vern ie r sca le

Lock nu t

P

Fig. 19.3 Bevel protector

19.2.1.7 Divider

It is used for marking and drawing circle and arcs on sheet metal.

19.2.1.8 Trammel

Trammel is used for marking and drawing large circles or arcs, which are beyond thescope of dividers.

19.2.1.9 Prick PunchFig. 19.4 shows the prick punch, which is used for indentation marks. It is used to make

small punch marks on layout lines in order to make them last longer. The angle of prickpunch is generally ground to 30° or 40° whereas for centre punch it is kept 60 °or 90°.

Prick punch

Center punch

60° or 90°

Fig. 19.4 Typical prick and centre punch

19.2.1.10 Centre Punch

Fig. 19.4 shows the centre punch, which is used for locating centre for indentation markfor drilling purposes.

Fitting 369

19.2.1.11 Surface Gauge or Scribing Block

Fig. 19.5 illustrate the surface gauge which is a principalmarking tool used generally in the fitting and the machineshops. It is made in various forms and sizes. It consists of acast iron sliding base fitted with a vertical steel rod. The scriberor marker is positioned or set into an adjustable device usinga knurled nut at one end. The scriber can be loosened ortightened by means of the nut. The marker is used to set itat any desired inclination, moved to and fro inside the holeaccommodating it or adjust its height along the vertical pillar.It is commonly used in conjunction with either a surface plateor marking table. It is used for locating centres of round rodheld in V- block, describing straight lines on work held firmlyin its position by means of a suitable device like angle plateand also in drawing a number of lines parallel to a true surface.This device is a very simple form of surface gauge and it islargely being replaced by a more accurate instrument calleduniversal surface gauge.

19.2.1.12 Universal Surface Gauge

Fig. 19.6 shows the universal surface gauge, whichis an improved variety of the surface gauge simplescribing block. It is designed in such as way thatappreciably finer adjustments can be made very quickly.It consists of a cast base perfectly machined and groundat the top, bottom and all sides. The base of the gaugeusually carries a V-shaped slot at the bottom so as torender it suitable for use on round objects. Two guidepins are provided at the rear end of the base, whichcan be pressed down to project below the base of thegauge. These pins can also be used against the edge ofthe surface plate or any other finished surface forguiding the instrument during marking and scribingwork. A swivel bolt is provided at the top of the basein which the spindle is fitted. This spindle can be swungand locked in any desired position by means of theadjusting screw, which is provided with a knurled nutat its end for this purpose. For marking purposes, thescriber is fitted in an adjustable screw on the spindleand is capable of being adjusted at any inclination and height along the spindle. A rocker isprovided at the top of the base and it carries an adjusting screw at its rear end. Duringoperation, the spindle is secured in the swivel bolt and is set at a desired inclination. Theadjustable scriber is swiveled and set at approximately the required height. On bringing thepoint of the scriber at the exact correct height, finer adjustments are then made usingadjusting screw provided on the rocker. Therefore, this gauge is commonly employed forscribing parallel lines at desired heights from a plane surface, comparing the trueness of twosimilar heights, setting out a desired height and similar other operations, and forms anindispensable instrument of bench work.

Spindle

Base

Scriber

Fig. 19.5 A surface gauge or scribing block

Scriber

Sp indle

C lam p

C lam p screw

Pin Base

Pin

Fig. 19.6 A universal surface gauge


19.2.2 Measuring DevicesThere are some general purpose measuring devices such as fillet and radius gauge, screw

pitch gauge, surface plate and try square which are described as under.

19.2.2.1 Fillet and Radius Gauge

Fig. 19.7 shows the fillet and radius gauge, which is similar in construction to a screwpitch gauge and carries a similar metal case containing a number of steel blades in it. Oneset of blades, mounted on one end of the case carries concave end faces and the other setat the other end of the case, carries blades, which have convex end formations. The radii ofthe curvatures of the end formations are of different dimensions and thus provide a fairlywide range for quick checking and measuring of curvature. This instrument is highly usefulfor measuring and checking the inside and outside radii of fillets and other round surfaces.The fillet and radius gauges are made in thin strong strips curved to different radii at end.The use of this gauge is depicted through Fig. 19.8.

W ork

W ork

Fig. 19.7 A fillet and radius gauge Fig. 19.8 A use of fillet and radius gauge

19.2.2.2 Screw Pitch Gauge

Fig. 19.9 shows the screw pitch gauge, which is ahighly fool-proof, very effective and fairly accurateinstrument used to identify or check the pitch of the threadscut on different threaded items. It consists of a case madeof metal carrying a large number of blades or threadedstrips which have teeth of different pitches, cut on theiredges and markings corresponding to these pitches on theirsurfaces. In operation, different blades are applied or triedon the threads one after the other and when any one ofthem is found meshing with the cut teeth, the relevantreading is read directly from the marking on the matchingblade surface. This gauge can be commonly used to measure or check the pitches of bothexternal and internal threads. The free ends of the screw pitch gauge blades are generallymade narrow for enabling them to enter the hollow parts easily while checking the internalthreads. In some instruments, the blades are made to have markings both for the pitches aswell as a value equal to double the depth of the threads. The latter quantity helps indetermining quickly the drill size to be used before tapping.

19.2.2.3 Surface Plate

Fig. 19.10(a) shows the surface plate, which is a cast iron plate having generally a squaretop well planed and square with adjacent machined faces. The top surface of the plate isfinished true by means of grinding and scrapping. It possesses a cast iron base, which is also

3 0-.

0 57

27-.0

6426

-.042

22.07

2

201.0

85

16-.0

96

Fig. 19.9 A screw pitch gauge

Fitting 371

machined true to keep the top surface of the plate in a perfect horizontal plane. Its specificuse is in testing the trueness of a finished surface, testing a try square, providing adequatebearing surface for V-block (Fig. 19.10(b)) and angle plates, etc. in scribing work.

Face

Cast plate

Hand le

Cast base

Fig. 19.10(a) A surface plate

Surface p la te

V-B lock

Surface gage

Shaft

Fig. 19.10(b) A use of surface plate and v-block

19.2.2.4 Try Square

Fig. 19.11 shows the try square, which is also known asengineer’s try square. It is very important tool required forscribing straight lines at right angles to a true surface ortesting the trueness of mutually normal surfaces. It is madein different sizes out of steel pieces. In construction, it issimilar to a carpenter’s try square but is comparatively moreaccurate. It can be made either in one piece or in two pieces.It consists of a steel blade fitted into a steel stock of rectangularcross-section. It is sufficiently hardened and tempered to suitthe need. Some precision kind of try squares is made withtheir blades having beveled edges properly ground and finishedsquare. Both inner and outer surface of the blade are kept truly at right angles to thecorresponding surfaces of the stock. In order to maintain this trueness, this tool should behandled with due care and should never be used as a striking or supporting tool or otherwork. The accuracy of this tool should be frequently checked to ensure the trueness as itaffects the accuracy of the finished job to a significant extent.

For checking the accuracy or trueness of a try square, the try square is made to lie flaton the top surface of a surface plate with the stock touching a machined edge of the plate.A straight line is marked along the outer edge of the blade and then the square turned overto take a new position. Another straight line is described along the outer edge of the bladein this new position of the try square. If both lines coincide with each other as they seemsto be as one line only, then the try square can be said as true.

19.2.3 Measuring InstrumentsSome common measuring instruments generally used in bench work or fitting shop are

micrometer, vernier caliper, depth gauge, and vernier height gauge. These are discussed as under.

Beam

Blade

Fig. 19.11 A try square


19.2.3.1 Micrometers

The micrometers are commonly employed for measuring small dimensions with extremeaccuracy of 0.01 mm. They may be of the three kinds -

(a) External micrometer for measuring external dimensions,

(b) Internal micrometer for measuring internal dimensions, and

(c) Depth micrometer for measuring depths.

For measuring a dimension in external micrometer, the work piece is held between thefixed anvil face and the spindle face of the micrometer. The spindle of the micrometer isallowed to move linearly towards the work by rotating thimble. When the spindle will touchthe work piece properly, the ratchet will give its sound. The small locking lever is thenrotated to clamp the spindle so that reading can be taken more accurately. Outside micrometersare used for measuring the outside dimensions of jobs, such as diameter of a bar, rod andthickness of plate. Generally, until and unless they are provided with the vernier attachment,the former can read up to 1/1000 or 0.001 inch and the latter up to 0.01 mm. The former areknown as inches micrometers and the latter metric micrometers, which are gradually replacingthe former due to the introduction or adopting of metric system. Inside micrometers arecommonly used for measuring inside dimensions of the objects, such as inside dia. of a hole,width of a slot or cavity, etc. The outside micrometers are the most extensively used inindustrial applications. All the micrometers, irrespective of the fact as to whether they carrygraduations in inches or millimeters, are similar in construction. An out side micrometer isdiscussed as under.

OUTSIDE MICROMETERFig. 19.12 shows an outside micrometer. It consists of the following main parts.

1. Metallic frame2. Axial graduated sleeve3. Circumferential screwed spindle4. Hardened steel anvil5. Thimble6. Ratchet stop screw7. Lock nut

0 5 20

15

10

AnvilSp indle Lock

nutS leeve Th im b le Ratche t

s top

Fram eJob

Fig. 19.12 Outside micrometer

Micrometer works commonly on the principle of nut and bolt assembly. The sleevecarries inside threads at the end, which forms the nut, and the screwed part of the spindlepasses through it. The spindle and the thimble are secured to each other such that by rotating

Fitting 373

the thimble the spindle rotates. With the result, when the thimble is revolved, it advancestowards or retards away from the fixed anvil, together with the spindle of the micrometer.The sleeve carries the graduations, which, in conjunction with the beveled and graduated partof the thimble, give the measure of the opening between the end faces of the anvil and thespindle. The ratchet arrangement provided at the end of the thimble prevents the spindlefrom pressing further against the surface of the piece being measured after the required feelhas been attained, thus facilitating a uniform reading and preventing the instrument frombeing damaged. Lock nut or locking lever is used for locking the micrometer for a desiredamount of time after taking or setting the reading. The construction of the outside micrometeris discussed as under.

COMMON PARTS OF OUTSIDE MICROMETER(1) Frame. The U frame of micrometer is made of steel, cast steel, malleable cast iron

or light alloy.

(2) Hardened anvil. It protrudes from the frame for a distance of at least 3 mm forholding and supporting the jobs for measurement.

(3) Screwed spindle. It does the actual measuring and possesses threads of 0.5 mmpitch.

(4) Barrel or Sleeve. It has datum or fiducially line and fixed graduations.

(5) Thimble. This is a tubular cover fastened with the spindle and moves with thespindle. The beveled edge of the thimble is divided into 50 equal parts, every fifthbeing numbered.

(6) Ratchet. This part is commonly recognized as friction stop of the micrometer,which acts as a precautionary measure also. It is a small extension to the thimblein which the ratchet slips when the pressure on the screw exceeds a certain amount.This produces uniform reading and prevents any damage or distortion of theinstrument.

(7) Spindle clamp. It is used to lock the instrument at any desired setting or at anyparticular reading .

READING ON MICRO METERIt works on the fine assembly of nut and bolt principle where pitch of both nut and bolt playsa big role. The graduation on the barrel of micrometer is in two parts, namely one above thereference line and the other below. The higher line graduation above the reference line isgraduated in 1 mm intervals. The first and every fifth are long and numbered 0, 5, 10, 15,20 and 25. The lower or small graduations are graduated in mm intervals but each graduationshall be placed at the middle of the two successive upper graduations to be read 0.5 mm. Themicrometer screw has a pitch of 0.5 mm, while the thimble has a scale of 50 divisions roundits circumference. Thus, on making or rotating through one complete turn, the thimblemoves forward or backward by one thread pitch of 0.5 mm, and one division of its scale is,therefore, equivalent to a longitudinal movement of 0.5 × 1/50 mm = 0.01 mm. It is the valueof one division on the thimble, which is the least that can be correctly read with the help ofa micrometer and is known as the least count. For measurement, the job is kept betweenthe end of the spindle and the fixed anvil, which is fitted to the frame. When the micrometeris closed, the line marked 0 (zero) on the thimble coincides with the line marked 0 (zero) onthe graduated sleeve. In metric outside micrometer, the pitch of the spindle screw is 0.5 mm


and the graduations provided on the spindle of themicrometer are in millimeters and subdivided into0.5 mm. Now in one turn of the thimble of themicrometer, owing to the 0.5 mm. pitch of thespindle screw, the spindle will move through 0.5mm and therefore, the corresponding openingbetween the faces of the fixed anvil and the spindlewill be 0.5 mm. This opening will go on increasingby the same distance 0.5 mm for each furtherrotation of the thimble. The beveled edge of thethimble carries 50 equal divisions on its peripheryin which every 5th division is marked. It is seenabove that for one complete turn of the thimblethe spindle moves through 0.5 mm. Now let thethimble is rotated one small division on its bevelededge i.e. 1/50 of the turn. The correspondingdisplacement of the spindle will then be 0.5 × 1 /50 = 0.01mm.

Depth micrometer is used for measuring depth ofholes and is shown in Fig. 19.13. Screw threadmicrometer (Fig. 19.14) is used to measure the pitchdiameter of the thread to an accuracy of 0.01mmand 0.001 inches. It comprises of similar parts asthat of outside micrometer accept the shapes of fixedand moveable anvils. The fixed and moveable anvilspossess the thread profiles for thread adjustmentfor measurement of the pitch diameter.

Fig. 9.14 A screw thread micrometer

19.2.3.2 Steel Rule

It is the simplest measuring tool just like a scale used in fitting shop. A six inch semiflexible rule is shown in Fig. 19.15 Other types of rules are described in the chapter oncarpentry shop. Most of the dimensions are measured by the steel rule in workshops.

1 2 3 4 5

Fig. 9.15 A steel rule

Ratche t s top

Th im b le

Sleeve

Locking ring

Head

Spindle

Fig. 9.13 A depth micrometer

Fitting 375

19.2.3.3 Caliper

Calipers are generally of two types inside and outside to make internal or externalmeasurements. They do not have direct scale reading. They transfer the measurement fromjobs to scale or vice versa. Fig. 19.16 shows a simple outside caliper. The caliper is held ina rule as shown in Fig. 19.17 to read the size. It is used to make external measurement suchas thickness of plates, diameter of sphere and cylinders. Fig. 19.18 shows the standard springjoint outside caliper.

1 2 3 4

Fig. 9.16 A simple outside Fig. 9.17 A caliper held in rule Fig. 9.18 A standard spring caliper joint outside caliper

19.2.3.4 Vernier Caliper

Fig. 19.19 shows the vernier caliper, which is commonly used to measure accurately

(1) outside diameters of shafts,

(2) thicknesses of various parts,

(3) diameters of holes or rings and

(4) internal dimensions of hollow jobs or articles.

0 3 4 51

0 5 15 25

6

Fine adjustm ent clam p

M ain scale

Fine adjustm ent screw

Vern ie rS lid ing jaw

Fixed jaw

M easuring faceJob

Fig. 19.19 A vernier caliper

It works on the principle of vernier and can measure the dimensions to an accuracy of0.02 mm. For making a measurement of external dimensions, the job is placed between the


fixed and the movable jaws. The movable or the sliding jaw is moved until it almost contactsthe job kept against the fixed jaw. The sliding jaw assembly of the vernier caliper that carriesthe fine adjustment screw should be clamped to the graduated beam with the help of adjustmentclamp. The two jaws are then brought into contact with the job by moving the sliding jawwith the help of fine adjustment screw. The jaws should make now definite contact with thejob but should not be tight. The main slide assembly is then locked to the beam with helpof clamp. The caliper is then carefully removed from the job to prevent springing the jawsand the reading is taken. For making a measurement of internal dimensions, the job is placedoutward between the fixed and the movable jaws meant for measuring inner dimension.

19.2.3.5 Vernier Depth Gauge

Vernier depth gauge is basically employed for checking depths of blind holes such asgrooves, slots, depth of key ways and heights of shoulders, etc. The principle on which itworks is the same as that of a vernier caliper. It is available with similar measuring accuraciesas the vernier caliper and readings are taken the similar manner. It consists of a movablehead with a base, which moves along the beam. A main scale on the beam and vernier scaleon the sliding head with fine adjustment screw are incorporated in the similar manner as ina vernier caliper.

19.2.3.6 Vernier Height Gauge

Fig. 19.20 illustrates the vernier height gauge, which is employed for measuring theheight of parts and in precision marking work. It consists of a heavy base, an accuratelyfinished bottom, a vertical bar mounted square to the base, carrying the main scale, a slidinghead with vernier, an auxiliary head with fine adjustment screw and nut and a bracketattached to the sliding head. This bracket is provided with a clamp by means of whichinterchangeable jaws can be fixed over there. The jaws can be fixed for measuring height orreplaced by scribing jaws according to requirement or need. The graduations on the heightgauge are given in Fig. 19.21.

G uiding edge

Scale

Fine adjustm ent screw

C lam p

Beam

Base

Slider

Depth o f m easuring jaw

Lower face o f jaw

M easuring jaw

Scriber

Upper face o f jaw(M easuring face)

Fine adjustm ent c lamp

Vern ie r sca les

Slider clam ping screw

Fig. 19.20 A vernier height gauge

Fitting 377

0 10 20 30 40 50

2 3 4 5 6 7 8

0 5 10 20 25

7 8 9 10

15

1 2 m m

49 m m

Fig. 19.21 A graduation on the vernier height gauge

19.2.3.7 Wire Guage

The wire gauge is a flat and circular steel sheet metal piece having slots all along itsperiphery as shown in Fig. 19.22. These slots have different standard sizes, which are engravednear their bottom. The size of each slot represents the correct diameter of the wire orthickness of the sheet of which it represents the gauge. The gauge number varies inverselyas the size of the wire. That is the higher the gauge number, the thinner the wire and viceversa.

1.5

1.7 5

2 .0

2 .25

2.5

2 .7 5

3 .0

3.54.0

5.0

0.25

0.37

0.440.50.56

0.620.75 0.89 1.0 1.12 1.

25 1.37

4.5

Fig. 19.22 A wire gauge

19.2.3.8 Dial Indicators

The dial indicators are also known as dial gauges and are shown in Fig. 19.23 (a, b). Theyare generally used for testing flatness of surfaces and parallelism of bars and rods. They arealso used for testing the machine tools. They are available in both metric as well as in inchesunits. Inches dial indicator of 0.001" measuring accuracy is in commonly used but they arealso available up to an accuracy of 0.0001". The commonly used metric dial indicator has anaccuracy of 0.01 mm. Those having 0.001 mm accuracy are also available, however they areused in highly precision measurement work.

19.2.3.9 Bevel Gauge

An adjustable bevel gauge is widely used for checking, comparing or transferring anglesand laying out work. It comprises of two adjustable blades, which can be positioned intoalmost any orientation to adjust any required angle. However, the direct reading is notobtained and the angle must be set or checked from some other angular measuringinstrument.


01 0

2 0

3 0

5 04 06 0

7 0

8 0

9 0

M A D E ININ D IA

1 0

5 0

1 5

6908

M A D E IN IN D IA

5

1 0

Fig. 19.23 (a) A continuous type Fig. 19.23 (b) A dial indicator ofdial indicator Brown and Sharp Co.

19.2.3.10 Combination Set

Combination set is an important instrument which has the combination of instrumentsnamely square head, a centre head, and a bevel protractor and sprit level as depicted in Fig.19.24. It is a very useful instrument frequently utilized in the bench work and machine shopmeasurements. The three portions of the combination set are used separately being heldin at any desired position by nuts which engage in a slot machined on the whole length ofthe beam at its back. The beam of the instrument acts as a rule, which is marked in inchesor centimeters or in both for measuring the length and height as and when required. Thesquare head possesses one edge square to the rule, giving a right angle, where as the otheredge form an angle of 45°. It is provided with a spirit level. The scale on the protractor maybe divided into degrees or a vernier attached whereby the angle can be measured in degreesand minutes. It is also fitted with a spirit level to help in leveling the work of setting itat an angle. The centre head with the rule fastened to it is called a centre square. It hastwo arms at right angles to one another and is so set on the rule that this angle is exactlydivided in two by the edge of the rule. It may be used to find the centre of a round bar orshaft. Spirit level is commonly used for checking levels and other measurement. It isdesigned to handle measurements, layout and checking of angles. The square head is usedfor checking 90° angle or as a square as shown in Fig 19.25. The protractor head may beutilized with a rule to measure angles or to measure the slope of a surface as shown inFig. 19.26.

19.2.3.11 Semi-circular Protractor

It resembles with a semi-circular protractor and is commonly used is geometrical drawings.Protractor used in sheet metal work is made from steel and often required for making ormeasuring angles.

Fitting 379

3489

3 4 8 9

Ru le

Centre head

Square head

Beve l p rotracto r

Sp irit-levelScriber

1 2 3 4 5 6 7 10 11

1 2 3 5 6 7 8 9 10 11

90°

Ru le

Fig. 19.24 A combination set Fig. 19.25 Checking 90° angle using combination set

45°Ru le

Square head

Fig. 19.26 Checking 45° angle using combination set

19.2.3.12 Slip Gauges

Slip gauges are also called as precision gauges blocks. They are made of rectangular blocksusing alloy steel, which are being hardened before finishing them to size of high degree ofaccuracy. They are basically used for precise measurement for verifying measuring tools suchas micrometers, comparators, and various limit gauges. The distance between two oppositefaces determines the size of the gauge. They are made in higher grades of accuracy. The grademost commonly used in the production of components, tools, and gauges is Grade I, for roughwork. Grade II and for checking other gauges. They are supplied in sets, the size of whichvaries from a set of about 112 pieces down to one containing 32 pieces. In English measurementthere are five sets containing 81,49,41,35 and 28 pieces. An 81-set has a wide range of combinationbut for general purpose a 49-set is usually preferred. The measurement is made by end to endassembly of slip gauge blocks and very little pressure in wring form is being applied.

19.2.3.13 Inspection Gauges

Inspection gauges are commonly employed to avoid costly and lengthy process of testingthe component dimensions. Fig. 19.27 represented the principle of limit gauging. Thesegauges are basically used for checking the size, shape and relative positions of various parts.These are of fixed type measuring devices and are classified as standard and limit. Standardgauges are made to the nominal size of the part to be tested and have the measuring memberequal in size to the mean permissible dimension of the part to be checked. Limit gauges or“go” and “no go” gauges are made to the limit sizes of the job to be measured. Sides or endsof the gauge are made corresponding to maximum and minimum permissible size of the jobfor its acceptance or rejection. The objective of limit gauges is to identify whether the actualdimensions of the work are within or outside the specified limits of acceptance. The double


end kind of limit gauge has the GO portion at one end and the NO GO portion at the otherend. GO portion must pass into or over an acceptable piece but the NO GO portion shouldnot pass. Inspection gauges may be classified as working, inspection, and reference or mastergauges. The working and inspection gauges are generally employed for inspection of componentsfrom stage to stage.

G oNot go

Low lim it

H igh lim it

Shaft

Fig. 19.27 A principle of limit gauge

Reference or master gauges are needed only for checking the size or condition of othergauges. The gauges are generally classified into:

1. Gauges for checking shafts

2. Gauges for checking holes

3. Gauges for checking forms

4. Gauges for checking threads

5. Gauges for checking tapers

The gauges commonly used in production work are

1. Progressive or step plug gauge (Fig. 19.28(a))

2. Thread plug gauge (Fig. 19.28(b))

3. A combination of internal and external non adjustable gauges (Fig. 19.28(c))For O D

G o

Not G oG o

NotG o

IDFor

(a ) Progressive o r S tep p lug G auge.

(b ) Thread plug gauge.

(c) A com bina tion of in te rna l and externa l non-adjustable gauges

Fig. 19.28 Types of gauges

Fitting 381

4. Ring gauge

5. Snap gauges (Fig. 19.29)

No

Go

No G o G o Go

F ixed anvils

Ad justab le anvils

Fig. 19.29 Snap gauges

6. Feeler gauge (Fig. 19.30)

.010.008

.006

.004

.003 .002 .0015

.015

.012

H industanLO C

K

Fig. 19.30 A feeler gauge

7. Wire gauge8. Template gauge9. Adjustable gap gauge (Fig. 19.31)

10. Screw pitch gauge (Fig. 19.9)11. Fillet and radius gauge

G oFixed anvils

Ad justab le anvil

No t G o

Fig. 19.31 An adjustable gap gauge

For manufacturing the above gauges, high carbon and alloy steels materials are commonlyemployed for manufacturing or production of gauges. Steel gauges may be used subject tosome distortion during hardening. These difficulties can be overcome by making gauges byuse of cemented carbide material or providing chrome plating at the surface of the gauge.


Plug Gauges

These are used for checking cylindrical, tapered, threaded, splined and square holesportions of manufacture components.

19.2.4 Holding ToolsHolding tools used in fitting shop comprises of basically vices and clamps. The clamps are

C or G clamp, plane slot, goose neck, double end finger, u-clamp, parallel jaw, and clampingblock. The various types of vices used in fitting shop are given as under:

19.2.4.1 Vices

The vices are hand vice, bench vice, machine vices, carpenter vice, shaper vice, leg vice,pipe vice, and pin vice.

19.2.4.1.1 Bench vice

Fig 19.32 shows a bench vice commonly used in fitting shop for holding a variety of jobs.

Fixed Jaw

JawPlate

Ho le fo rfixing

the vice

M ovable Jaw

Colla r

Hand le

BaseSp indle

Fig. 19.32 A bench vice

19.2.4.1.2 Machine vice

Fig 19.33 and Fig. 19.34 shows machine vice with swivel base and parallel jaw machinevice. These types of vices are commonly used in fitting shop for holding a variety of jobs. Theyare used for precision work on the machine table like shaping, milling, drilling and grinding.They are generally made of grey cast iron.

Jaw

Hand le

Body fixedon base

Sw ive l base

M ach ine v ice w ith sw ive l base .Paralle l jaw m achine v ice.

JawM ovable JawFix Jaw

Body

Fig. 19.33 A machine vice with swivel base Fig. 19.34 A machine vice with parallel jaw

Fitting 383

19.2.4.1.3 Universal swivel base machine vice

Fig. 19.35 shows a special type of universal swivel base machine vice made with swivellinghead. It is commonly used in fitting shop for holding a variety of jobs. The jobs after holdingin jaws can be adjusted at any angle either horizontally or vertically with the help of swellinghead.

Hand leJaw pla te

P ivo t

Sw ive l base

Fig. 19.35 A universal swivel base machine vice

19.2.4.1.4 Toolmaker’s vice

Fig 19.36 shows a small tiny vice known as tool maker vice. It is commonly used by toolmaker, watch maker, die maker and goldsmith for holding a variety of small parts for carryingsome operation.

Hand le

Base

Fig. 19.36 A tool maker’s vice

19.2.4.1.5 Hand vice

Hand vice is shown in Fig. 19.37 which is utilized for holdingkeys, small drills, screws, rivets, and other similar objects which arevery small to be easily held in the bench vice. This is made in variousshapes and sizes. It consists of two legs made of mild steel which holdthe jaws at the top and are hinged together at the bottom. A flatspring held between the legs which tend to keep the jaws open. Itsjaws can be opened and closed by a wing nut which moves through ascrew that is fastened to one leg and passes through the other.

19.2.4.1.6 Pin vice

Pin vice is used for holding round jobs of small diameter such as wire and pins, duringworking. It also forms a very useful handle for small files. It consists of a handle and atapered nose covering a small collet chuck at its end. The chuck carries the jaws which areoperated by turning the handle. It is commonly used by a watch maker.

W ingnut

Spring

Fig. 19.37 Hand vice


19.2.4.2 Clamping Divices

There are two types of clamps namely C clamp and tool maker clamp. A C-clamp isshown in Fig. 19.38 which is used for gripping the work during construction or assemblywork. Whereas tool maker clamp (Fig. 19.39) is used for gripping or holding smaller jobs.

Jaw

Screw

G ripp ing ends

Screw

Fig. 19.38 C-clamp Fig. 19.39 A tool maker clamp

19.2.5 Cutting ToolsThe important common cutting tools are discussed below

19.2.5.1 Files

The widely used hand cutting tool in workshops is the file. It is a hardened piece of highgrade steel with slanting rows of teeth. It is used to cut, smooth, or fit metal parts. It is usedfile or cut softer metals. It consists of the following parts as shown in Fig. 19.40. The tangis the pointed part, which fitted into the handle. The point is the end opposite the tang. Theheel is next to the handle. The safe edge or side of a file is that which has no teeth. It isclassified on bases of type or cut of teeth and sectional form.

Tang

EdgeCuttingpoin ts

Hand leHeel

Face

Length

Fig. 19.40 Parts of a file

19.2.5.1.1 Size of a File

Size of a file is specified by its length. It is the distance from the point to the heel,without the tang. Files for fine work are usually from 100 to 200 mm and those for heavierwork from 200 to 450 mm in length.

19.2.5.1.2 Classification of Files

The files are classified on basis of type of cuts, grade and shapes. These are further subclassified as under

Fitting 385

(A) Type of Cut

The most commonly used files according to cuts of teeth are shown in Fig.19.41.

(i) Single

(ii) Double and

(iii) Rasp

(a ) S ing le cut file

(b ) Doub le cut file

(c) Rasp cut file.

60°

Fig. 19.41 Types of files according to cuts of teeth

(B) Grade of Cut

Files are cut with teeth of different grades. Those in general are

(i) Smooth

(ii) Second cut

(iii) Bastered

(iv) Rough

(C) Shape of File

Common shapes of files are having different cross sections, which cover most requirements.

19.2.5.1.3 Cut or teeth on files

Teeth or cuts of files can be categorized into two groups namely single cut and doublecut. In single cut files, the teeth are cut parallel to other across the file at an angle of about60° to the centre line of the file. Such types of file are named as flats and are widely usedon hard metal.

A double-cut file possesses two sets of teeth, the over-cut teeth being cut at about 60°and the up cut at 75 to 80° to the centre line.

Single-cut and double-cut files are further classified according to the coarseness or spacingbetween the rows of the teeth. In descending order of roughness, such files are listed as:

(i) Smooth

(ii) Dead smooth

(iii) Rough

(iv) Bastard


(v) Second cut

(vi) Super smooth

These files are used for finishing general surface work. Both faces of file are double cutand both edges are single cut. Such files are commonly tapered in width and thickness.

General classification of files based on shapes or cross sections are shown in Fig. 19.42along with their uses are as under:

19.2.5.1.4 Hand files

Hand files are commonly used for finishing surface work. Both faces of the file are doublecut. Either both edges are single cut or one is uncut to provide a safe edge.

19.2.5.1.5 Flat files

Flat files are generally used for filing flat surfaces in fitting shop.

19.2.5.1.6 Triangular files

Triangular files are commonly used for filing corners between 60° and 90°. They aredouble cut on all faces.

19.2.5.1.7 Square files

Square files are commonly used for filing in corners in jobs. They are double cut on allsides and tapers.

19.2.5.1.8 Round files

Round files are generally used for opening out holes and rounding inside corners. Rough,bastard, second cut and smooth files under 15 cm in length are single cut.

19.2.5.1.9 Half round files

These files comprises of flat and half round sides. The flat side of half round file is usedfor general work and the half round side for filing concave surfaces. These files are doublecut on the flat side. The curved side is single cut, smooth or second cut.

19.2.5.1.10 Knife-edge files

These files are commonly used for cleaning out acute-angled corners. The two faces ofthese files are double cut, while the edge is single cut. These files are made in sizes from10 to 20 cm of various shapes and cuts. They are extremely delicate and are used for finework such as pierced designed in thin metal.

19.2.5.1.11 Pillar files

These files are used for finishing narrow slots. Both faces are double cut and either bothedges are single cut or one is uncut to provide a safe edge of the file.

19.2.5.1.12 Needle files

Needle files are generally used for filling keys tooth wheels of clocks and other curvedsurfaces.

19.2.5.1.13 Mill files

Mill files are commonly used for filing half round recess and gullet of mill saw.

Fitting 387

1. Hand file

2 . Flat file

3 . Triangu la r file

4 . Round file

5 . Square file

6 . Ha lf round file

7 . Kn ife E dge file

8 . P illar f ile

9 . Need le file

Fig. 19.42 General classification of files based on shapes or cross sections

19.2.5.2 Scrapers

Scrapers are made up of old files and the cutting edge of scraper is hardened andtempered. They are mainly used to scrap metal surfaces by rubbing the work surface. Theyalso produce a bearing surface, which has been filed or machined earlier. The scrapers arehand cutting tools used for removing metal from surfaces in form of thin slices or flakes toproduce smooth and fine surfaces. Machined surfaces are not always perfectly true. If a verytrue surface is needed, the high spots must be located and removed. It is normally done withthe help of a scraper. The scrapers are made in a variety of lengths from 100 mm upwardsand in many shapes, depending upon the type of work to be done. The following types ofscrappers according to shape are commonly classified as

(i) Flat

(ii) Hook

(iii) Triangular

(iv) Half round

Fig 19.43 shows various scraper which aregenerally used for scraping job work in fittingshop. These are discussed as under.

19.2.5.2.1 Flat scrapers

Flat scrapers are commonly used forremoving slight irregularities on a flat surface.

Flat scrapperHand le

Hook scrapper

Triangu la r scrapper

Ha lf round scrapper

Hand le

Fig. 19.43 Common types of scraper


When the surface has been scraped with strokes in one direction, it must then be scrapedwith strokes at 90° to the first ones.

19.2.5.2.2 Hook scrapers

Hook scrapers are widely used for scraping minor job work in fitting shop.

19.2.5.2.3 Triangular scrapers

These are generally used to finish bearings in the same way as the half round scrapers, butsince they come to a sharp point at the tip they removes burrs at the edge of small holes whicha half round scraper could not enter. The faces of the scraper are hollow ground to give the toolthree cutting edges which are simpler to sharpen than the edges of the half round scraper.

19.2.5.2.4 Half-round scrapers

These types of scrapers are widely used for scraping internal cylindrical surfaces. Theyare used to remove high spots in bore & and bearings to give the right type of fit to themating shaft or journal.

Scrapers are stored carefully for protection of cutting edges from damage.

19.2.5.3 Chisel

Chisel is one of the most important tools of the sheet metal, fitting and forging shop. Itis widely used for cutting and chipping the work piece. It is made of high carbon steel or toolsteel. It is in the form of a rod having cutting edge at one end, hexagonal or octagonal bodyand striking head at the other end. The size of a chisel is described by its length and widthof edge. When the cutting edge becomes blunt, it is again sharpened by grinding. For cuttingthe job or work piece with the chisel, it is placed vertically on the job or work piece andhammering is carried out upon its head. But for chipping, the chisel is inclined at 40°-70° withthe job orwork piece. The angle of the cutting edge of the chisel is 35°-70°according to themetals to be cut.

19.2.5.4 Drill

Drill is a common tool widely formaking holes in a metal piece in fittingshop. It is generally held in chuck ofbench drilling machine shown in Fig.19.44. It usually consists of two cuttingedges set at an angle with the axis.There are three types of drills: (a) flatdrill, (b) straight fluted drill and (c) twistdrill. For fast and accurate drilling worktwist drills are commonly used. Ageneral twist drill comprises the cuttingangle of 118° and to obtain the correctdiameter of the hole. It should beground with both lips at 59° to the axisof the drill, with equal lengths of thecutting edges. The various hand drillsand their operations are shown inFig. 19.45.

Belt housing

Controls

M otor housing

O pera ting lever

Lockinghandle

Drill chuck

Transparentguard

Base

The B ench D rill

Tab le

Fig. 19.44 A bench drilling machine

Fitting 389

Breast drill

E lectric drill

Pneum atic dr ill

Hand d rill

D rill chuck

Drill Job

Fig. 19.45 Types of hand drilling machine

19.2.5.5 Reamer

The drill does not always produce the correct hole some time with good finish. Thus acorrect hole is produced with good finish of a pre drilled hole using a reamer. A common handreamer is shown in Fig. 19.46. It is commonly employed to remove minimum amount ofmetal (100 to 150 micron for rough reaming and 5 to 20 micron for fine reaming) from thehole. During reaming operations, the job should be properly supported and rigidly held. Astock wrench of appropriate size for holding the reamer is used. The reamer must be keptin its correct position relative to the job. It must be run slowly and excessive feed must beavoided. It should be always be turned in the cutting direction. Sufficient amount of cuttingfluid should also be employed. When removing the reamer, it must be turned in the cuttingdirection. Reamers with blunt or chipped edges must not be used.

Hand Ream er

Taper on end ofhand reamer

Fig. 19.46 A common hand reamer


19.2.5.5.1 Types of reamers

The reamers are classified as under.

(i) Hand reamer

(ii) Machine reamers

(iii) Parallel reamer

(iv) Taper reamer

(v) Reamers with straight flutes

(vi) Reamers with spiral flutes

(vii) Adjustable reamer

(viii) Expanding reamer

Some common types of reamer generally used in fitting shops are discussed as under.

19.2.5.5.1.1 Hand reamer

Hand reamer is operated or rotated by hand to finish holes and remove its ovality. Itscutting edges are backed off in the same manner as those of twist drills to give suitableclearance. It is made up of carbon or high speed steel. It is used for very fine internal turningin the hole by placing a tap wrench on the squared end of the reamer.

19.2.5.5.1.2 Machine reamer

Machine reamer is designed for slow speeds for use on drill presses, lathes, verticalmilling machines etc. It is chamfered on the front side of cutting edge. It possesses straightor tapered shanks and comprises of either straight or spiral flutes.

19.2.5.5.1.3 Taper reamer

Taper reamer is widely used for finishing taper holes smoothly and accurately. It is alsoused to provide a taper to a drilled hole when a taper pin is to be used. It is generallyperformed with either straight or spiral flutes. It has spaces ground into the cutting edgesor teeth to prevent overloading the entire length of each tooth of the reamer. These spacesare staggered on the various teeth to help in stock removal. The spiral fluted reamer has ashearing action that eliminates chatter and is generally preferred. Large size taper reamersare made in both roughing and finishing types. When a large amount of stock is to beremoved, a roughing reamer is generally used. The finishing reamer is commonly employedto control size and smooth the hole.

19.2.5.5.1.4 Spiral fluted reamer

Spiral fluted reamer performs greater shearing action than one with straight flute.

19.2.5.6 TAPS

Taps are used for cutting or producing internal threads of either left or right hand kindin nuts or pre-drilled holes. Taps are threaded externally. The threads being cut by grindingto give a high class finish. Taps are made up of alloy steel or hardened steel. To providecutting edges, grooves known as flutes are ground along the threaded portion of the tap sothat the thread is divided into rows of teeth. The number of flutes on tap varies from twoto eight whereas four being the most common. The flutes acts as channels to carry away thechips formed during tapping or cutting threads. The nomenclature of a typical tap is shown

Fitting 391

in Fig. 19.47. Taps are may be of many types such as hand taps, machine taps, pipe taps, solidtaps, straight and bend shank taps. Hand taps are usually made in sets of three: (1) taper tap(2) plug tap (3) bottoming tap as shown in Fig. 19.48. The taper tap is tapered off for 8 or 10threads, and is used first, cutting to the full thread gradually. The intermediate tap usuallyhas two or three threads chamfered. The second tap can finish a through hole. The plug taphas a full-sized un-tapered thread to the end and is the main finishing tap. In the case of blindhole, a plug tap must be used.

Thread re lie f(Radial)

Length o f shank Length o f bodyCham fer

Cutting face

Flute

Heel

Land

O vera ll leng th

Length o f Sq

Sha

nk

Dia

Poi

nt

Dia

Fig. 19.47 Nomenclature of tap

Taper tap

Plug tap

Bottom ing tap

Fig. 19.48 Types of hand taps

19.2.5.7 Hand snip or shear

Various kinds of snips or shears are described in chapter pertaining to sheet metal work.They are commonly employed for cutting or shearing metal sheets to required shapes andsizes. Few snips are available for making straight or circular cuts. The most common typesof snips in use are:

(a) Straight snips,

(b) Bent snips and

(c) Slitting shears

19.2.5.8 Hand hacksaw

Hand hacksaws are made in two types namely a fixed frame and adjustable frame orientedas shown in Fig.19.49 and Fig.19.50. The former possesses solid frame in which the lengthcannot be changed and where as the latter comprises the adjustable frame which has a backthat can be lengthened or shortened to hold blades of different sizes. The hand hacksaws arecommonly used for sawing all soft metal. They consist of a frame, handle, prongs, tighteningscrew and nut, and blade as shown in figure. Its frame is made to hold the blade tightly. Howevera power operated hacksaw can also be used for cutting raw materials in sizes in case ofcontinuous cutting generally occurring frequently in fitting or in machine shops.


Fram e

Hand leBlade

W ing nut

Fig. 19.49 A fixed frame hacksaw

Stee l fram e

Hand le

B lade ho lder

Length o f bladeW ing nut

B lade

Bladeholder

P in

Fig. 19.50 An adjustable frame hacksaw

19.2.6 Sriking ToolsVarious types of hammers (such as ball peen hammer, straight peen hammer, cross-peen

hammer, double face hammer and soft face hammer) are acting as striking tools. These typeshave been described in chapters relating to sheet metal work and forging work. The commontype of ball peen hammer and their parts are shown in Fig. 19.51.

Ball pe in

Pe in neck

Cheek Length o f handle

Eye ho le

Po le neck

Po le

Face

Fig. 19.51 Common type of ball peen hammer and their parts

19.2.7 Tightening ToolsThe tightening tools include pliers, screw driver and wrenches, which are discussed as

under.

Fitting 393

19.2.7.1 Pliers

Pliers are namely ordinary needle nose and special type. Fig 19.52(a) shows a long nosepliers and Fig. 19.52(b) shows a combination pliers. These are commonly used by fitter andelectrician for holding a variety of jobs.

(a ) Long nose p lie rs. (b ) Combination p liers.

Fig. 19.52 Long nose pliers and combination pliers

19.2.7.2 Screw driver

Screw driver is a screw tightening tool. The most commonly used standard screw driverwith its parts is shown in Fig 19.53. It is generally used by hand for tightening the screws.It is also of various types depending upon the kind of work.

Hand leFerru le

Shank Blade

Po in t

Length o f shankLength o f hand le

Fig. 19.53 Standard screw driver with its parts

19.2.7.3 Wrenches

Wrenches are commonly known as spanners. These generally come in sets and arecommonly identified by numbers. These are of various types and few general types involveopen single ended, open double ended, closed ended adjustable, ring spanner, offset socket,t-socket, box wrench, pipe wrench and Allen wrench.

19.3 OPERATIONS PERFORMED IN FITTING WORK

The operations commonly performed in bench and fitting work may be classified asunder.

1. Marking 2. Chipping

3. Filing 4. Scrapping

5. Sawing 6. Drilling

7. Reaming 8. Tapping

9. Grinding and 10. Polishing

Some common operations are discussed as under.


19.3.1 GrindingGrinding is generally called as fine machining or finishing operations of removing materials

from surface usually 0.25-0.50 mm in most operations through the use of grinding wheel.Grinding wheel is highly useful in removing extra unwanted metal and sharpening cuttingtools such as chisels, drill, taps, and other cutting tools. It may be used to finish almost allsurface, which has been previously roughly shaped by some other processes or to remove theextra material which is too hard to be removed by other machining processes. The accuracyin fine grinding is in few microns or even less. In grinding, the work is held pressed againstthe high speed rotating grinding wheel and the metal gets reduced by abrasion. Grindingwheel is generally made from silicon carbide or aluminium oxide. It is generally made up ofparticles of hard substance called the abrasive and is embedded in a matrix called the bond.These abrasives form the cutting points in a wheel and are termed as grains. The abrasivesare of generally two types namely natural and artificial. Emery and corundum are two naturalabrasives, while carborundum and aloxite are artificial abrasives. The hardness or softnessof the wheel is dependent on the amount and kind of the bonding material. Generally, hardwheels of aloxite are used for grinding soft materials and soft wheels of carborundum forgrinding hard materials using various types of grinding machines known as grinders. In wetgrinding, large amount of coolant over the work and on wheel face is provided. Coolant willremove heat generated during grinding and promotes long wheel life and produces very goodsurface finish. The cutting face of a grinding wheel should be kept in a true, clean and sharpconditioned shape for obtaining efficient cutting. Suitable dressers are also employed periodicallyfor reconditioning and dressing of glazed or blunt wheels. Grinder may be various types suchas cylindrical grinder, surface grinder, pedestal grinder, tool and cutter grinder, centre-lessgrinder, internal grinder and jig grinder and profile grinder. Fig. 19.54 illustrates the surfacegrinding machine and principle of surface grinding. Fig. 19.55 illustrates the principle ofcylindrical grinding.

Down feed

G rind ing whee l

M agnetic chuck

(a)

W heel head feed

G rind ing whee lW ork p iece

Tab le feed

Longitud inal feed

(b)

M agnetic chuck

Fig. 19.54 Surface grinding machine and its principle

19.3.2 PolishingPolishing is surfacing finishing process for producing a flat, scratch-free, mirror-like

finish. It consists of fine grinding, intermediate grinding, rough polishing, and fine polishing.Initially the surface to be polished is roughly ground to remove deep cut off marks. Then theintermediate grinding is done with fine emery or silicon carbide (Carborundum) papersdecreasing in grit size in three to four stages to remove grinding marks. Emery papers are

Fitting 395

graded from fine to coarse. This polishing operation may be performed by hand or mechanicallyusing the rotating disks. The motion in polishing of work on polishing wheel should alwaysbe straight and the polishing strokes should cover the whole length of the surface beingpolished. Finer grade emery disc pr polishing wheel should be used for the fine finish work.Polishing is commonly performed on utensils.

G rind ing wheel

Tails tockCylindricalJob

Headstock

DogDrive p la te

Upper table

Lower table

Fig. 19.55 Principle of cylindrical grinding

19.3.3 Surface CoatingThe various manufacturing processes such as casting, forging, machining, hot working,

cold working and joining processes etc. produce different surfaces. Therefore for gettingdesired surface of the part, subsequent surface preservation processes are needed. Thesepreservation processes are called as surface coating of metals. Coatings on surfaces areemployed on most metal parts, either for protective or for decorative or for both purposes.The main objectives of coatings involve for the purpose of decoration, surface protection,corrosion resistance and providing of a hard surface. The surface covering with coating mustbe uniform and free from runs, checks or peelings. Coatings are commonly applied to thefinished components to form the final product. For successful coating, clean and smoothsurface finishes is required for assuring good adhesion during coating. Cleaning operationsare performed both preparatory to finishing operations and after finishing operations. Theyare primarily used to remove dirt, oil, oxides, scale, and other harmful ingredients thatultimately affect the life of the product. There are various methods of cleaning, drying, andcompetitive means of applying the coating. However, the various processes involved in preparingwork for coating and applying the coatings are closely interrelated. Galvanizing, parkerizing,electroplating and painting are the common surface coating processes employed for protectingthe surfaces of the work pieces.

19.4 QUESTIONS1. How will you classify the tools commonly used in fitting ?

2. Explain briefly the various clamping tools used in fitting shop using neat sketches.

3. Explain in brief with neat sketches the various types of measuring tools used in fitting shop.

4. Explain the construction and working of vernier caliper using neat sketch. How its least countcan be determined? What are its uses?


5. Explain the construction and working of micrometer with neat sketches. How its least countcan be determined?

6. Explain in brief the various types of cutting tools used in fitting shop using neat sketches.

7. Explain in brief the various precautions associated with hand hacksaw, files and chisels.

8. Explain in brief the various types of striking tools used in fitting shop using neat sketches.

9. Explain the various types of files used in fitting shop. How are they classified ?

10. Explain the following tools.

(i) Drill (ii) Reamer

(iii) Taps (iv) Die and die stock

11. Write short notes on the following operations:

(i) Marking (ii) Filing (iii) Chipping

(iv) Sawing (v) Drilling (vi) Tapping

(vii) Grinding (viii) Polishing (ix) Punching

12. What is the main difference between the hand hammers used in a smithy shop and a fittingshop?

13. What is the difference between hand hacksaw used in fitting shop and the saws used incarpentry shop?

14. Write short notes on the following:

(i) Polishing (ii) Buffing (iii) Boring

(iv) Milling (v) Broaching (vi) Shaping

(vii) Grinding.

15. How will you achieve the following?

(i) Rate of production (ii) Accuracy and

(iii) Surface finish


152

CARPENTRY

9.1 INTRODUCTION

Wood obtained from tree is the chief product of forest. It has been universally acceptable asraw material for manufacturing wooden products or appliances. From the pre-historic times,wood has been utilized an important source of getting heat by firing it. It has been utilizedas an mazor construction material for making shelter for the basic need of human being. Asthe civilization advanced, it gained tremendous importance as special material for boat-building, for piling to support docks and railroad tracks. But in modern times, with theadvance of wood chemistry, the uses of wood have recognized its importance in manufacturingcheap useful products used in day today life such as paper, furniture, textiles, plastics andhundreds of chemicals and extractives. The wooden products as plywood have superseded insome products in comparison metallic and ceramic materials. Compressed wood has alsoreplaced some metals for gears and die casts. In war-time, in Europe, wood has been usedas a source of wood gas for propelling automobiles. Similarly clothing has-been made fromwood cotton and wood wool. The useful work on wood is being generally carried out in a mostcommon shop known as carpentry shop. The work performed in carpentry shops comprisesof cutting, shaping and fastening wood and other materials together to produce the productsof woods. Therefore, carpentry shop deals with the timber, various types of tools and the artof joinery. In wood, there are two types of cells namely radiating outward from the centerof wood cross-section and running parallel to the length of wood. Trees are generally classifiedinto exogenous and endogenous types according to manner of growth.

Exogenous types are also known as outward growing trees which produce timber forcommercial use. They grow outward and the additional growth which occurs each year takesplace on the outside of the trunk just underneath its bark, while the innermost timbercontinues to mature. Each time the growth cycle is completed the tree gains one more growthring or annual ring. In counting these rings, the age of a tree can be determined, as eachring represents one year of growth.

Endogenous trees are also known as inward growing. They grow inwards i.e., every freshlayer of sapwood is added inside instead of outside. Cane, bamboo and coconut are examplesof such endogenous trees.

Timber is a common name imparted to wood suitable for engineering, construction andbuilding purposes. Timber is obtained from trees by cutting the main body of tree in thesuitable sizes after the full growth of tree. The timber structure is consisting of annual rings,

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heartwood, sapwood, pith, cambium layer, bast, medullary rays and bark. Commercial timbersare commonly classified into hardwoods and softwoods. Hardwoods comprises of oak andbeech that have a broad leaf. Whereas softwoods include pine and spruce which have narrowneedle like leaf.

This chapter presents the various kinds of material, tools and equipments used in carpentryshop along with their properties and uses.

9.2 HARD AND SOFT WOOD

Hard wood is generally obtained from broad leaves or deciduous trees where as the softwoodfrom trees having needle shaped yes or conifers. The major differences between hard woodand soft wood are given as under.

Table 9.1 Difference between Hard Wood and Soft Wood

S.No. Hard Wood Soft Wood

1 It is dark in color Its color is light

2 It is heavy in weight. It is light in weight

3 Hard woods are harder and denser. Soft woods are comparatively lighter

4 It has less resin content Few softwoods are resinous.

5 It does not split quickly It gets splitted quickly

6 It is difficult to work. It is easy to work.

7 It’s annual rings are close and often Its annual rings are well spaced and quitindistinct distinct

8 It is slow growing. It is fast growing.

9 It has good tensile and shear resistance. It has good tensile resistance but is weakacross the fibers.

10 It does not catch fire very soon It catches fire very soon.

9.3 TYPES OF COMMON TIMBERS, THEIR QUALITIES AND USESThe common types of well recognized timbers available in India are Shisham, Sal, Teak,Deodar, Mango, Mahogany, Kail, Chid, Babul, Fir wood, Walnut and Haldu,. Out of these,Deodar, Chid, Kail, Fir wood and Haldu fall in the categories of softwoods and Shisham, Sal,Teak, Kiker, Mango, Walnut fall in the categories of hardwoods. Some of the other foreigntimbers commonly used in India are Ash, Burma, Hickory, Oak and Pine.

1 Shisham is dark brown in color and it possesses golden and dark brow stripes. Itis very hard to work and generally wears or blunts the sharp edge of cutting toolvery soon. It is available in India in Himalayan range at heights from 1000-1500meters and in deep forests. It is recognized as highly strong and durable wood andit is mainly used for making good variety of furniture, tool handles, beds, cabinets,bridge piles, plywood etc.

2 Sal exists in rose brown color which slowly turns into dark brown. This wood iscommonly available in India in Himalayas, M.P and U.P. It is free from attack ofwhite ants insects and it is very difficult to work. It has poor finish and therefore


is not used for decorative furniture. It finds tremendous applications in makingdoors, windows, cots, wooden handles, furniture and railway sleepers etc.

3 Teak wood is hard, very costly and it possesses wide applications. It is availablein golden yellow or dark brown color. Special stripes on it add to its beauty. In India,it is found in M.P. It is very strong, durable and it maintains good polish. It ismainly used for making good quality furniture, plywood, ships etc.

4 Deodar is white in color when soft. But when it is hard, its color turns toward lightyellow. It is strong and durable. It provides fragrance when smelled. It is not easilyattacked by insects as it has some quantity of oil in it. It is commonly available inHimalayas at a height from 1500 to 3000 meters. It is used for manufacturing ofdoors, furniture, patterns, railway sleepers etc.

5 Mango is brown in color and it can be easily shaped in various products. It is widelyused in India as a cheap wood for making doors, packing cases, toys and inferiorfurniture.

6 Mahogany is reddish brown in color which is highly durable when dry. It alsocontains some oil in it that prevents it from the attack of insects. It is commonlyutilized for manufacturing cabinet, fine furniture, pattern making work etc.

7 Kail wood possesses too many knots in it. This wood is commonly found in Himalayasof India. It yields a close grained, moderately hard and durable wood which can beeasily painted. It is commonly utilized for making cheap furniture, wooden doors,packing case etc.

8 Chid is also known as Chir. Its color is dark brown when is soft, but it is reddishbrown when hard. It has stripes of dark brown color. It has oily smell and is usedfor interior work in the house.

9 Babul is close grained tough and pale red colored wood and is used for making toolhandles etc.

10 Fir wood is light brown in color when soft but harder variety is found in darkbrown color. It can be easily attacked by insects. It is commonly utilized for makingdrawers, packing cases, doors etc.

11 Walnut is a good variety of wood which resists the attack of white ants. It can bepolished easily in a better way. This wood is generally used for making musicalinstruments, furniture, cabinet work, decoration work etc.

12 Haldu is white in color at the time of cutting, but once cut, its color becomesyellow. It can be dried and polished satisfactorily. It is widely used for making smallobjects such as stool, picture frames, trays, cabinet etc.

9.4 FELLING, CONVERSION AND SEASONING OF WOOD

Cutting of living or standing trees to obtain timber is called felling of trees. Trees are cut atappropriate time. The best time for sawing the tree is immediately after the tree has achievedits full growth or maturity age so that the maximum quantity and best quality of wood canbe obtained. If an immature tree is cut, it will carry a lot of sapwood which may not be muchuseful for the carpentry work. Contrary to this, if the tree is allowed to stand for long afterattaining the maturity the most valuable part of timber will be subjected to decay. Thereforeenough care must be taken to see that felling is accomplished only at the appropriate time.

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The proper time of cutting of a tree depends largely on its age and season of the year. Cuttingof trees for getting wood for use is done generally in mid-summer or mid-winter because thesap of the tree is at rest during this period and therefore, the chances of any decay of usefulwood are minimized. The time taken for a tree to mature depends whether it is softwood orhardwood. The softwood tree will mature after 80 to 100 years whereas hardwood will takemore time between 130 and 200 years for getting mature. After cutting the trees from bottom,the branches are removed from it and form of log is obtained. The process of sawing woodenlogs into useful sizes and shapes (boards, planks squares and other planes section and sizesetc.) for market or commercial requirements is known as conversion. Conversion is carriedover prior to seasoning by two methods namely plain, through, through sawn process andquarter and rift sawn process. Plain sections of wood may likely to warp and hence cannotbe used for quality work. Quarter sawing almost eliminates the chances of warping. Quartersawn sections are used as quality wood in cabinet making, decoration and framework. Plantationof new trees is also essential and that should be carried out form time to time.

Conversion means sawing of timber logs into different commercial sizes. A notable featurein conversion is to provide an adequate allowance for shrinkage that takes place duringseasoning of sawn or converted wood. The shrinkage of wood usually varies between 3.2 mmto 6.4 mm, according to the type of wood and its time of cutting. The three methods ofconversion commonly adopted are discussed as under.

The first method is called as flat or ordinary cutting which is the simplest procedure ofsawing but the cut sections are likely to warp. Therefore, the wood cut through this procedurecannot be called as quality work. In this method, the timber log is cut into a number of boardsby taking various parallel saw cuts into the suitable forms.

The second method is known as tangential cutting in which cutting takes place in sucha way that the widths of the boards are tangential to the annual rings. The timber cut bythis method is seasoned quickly and cutting wastage is also less but it may warp like flat sawnwood.

The third procedure is known as quarter or radial sawing in which the timber logs aresawn so that the width of the sawn boards falls along the medulary rays which mean theyrun across the section of the log. The normal defect of warping is almost eliminated by thisprocedure of sawing and the timber is very suitable for all sorts of wood work involvingcabinet-making, decoration and framework. Trees are converted into the following usefulmarketable forms such as posts (square pieces of timber 175-300 mm wide or round piecesof 175-300 mm in diameter), deals (225 mm wide and about 100 mm thick parallel side pieces),planks (50 to 100 mm thick, 275-300 mm wide and 3 to 7 meters long) and boards or battens(25 to 50 mm thick and 125 to 175 mm wide). Sizes of timber (Kail, Deodar etc.) available inthe market for building construction purposes are 10' × 10" × 5" or 12' × 10" × 5" or 10' ×8" × 5" or 10' × 8" × 4" etc.

Seasoning of wood is the reduction of the moisture or sap content of it to the pointwhere, under normal conditions of use, no further drying out will take place. The mainobjective of seasoning is to reduce the unwanted amount of moisture from the timber. As themoisture contained in the cell walls evaporates, shrinkage of the timber takes place whichis greatest along the growth rings. Certain other defects such as shaking and warping maydevelop during seasoning. Therefore for these reasons green or unseasoned timber should notused for any work but for rough work. Once the timber is seasoned before use, it will notshrink, twist or swell during its further use. Need for seasoning of timber before its use is


necessary in order to achieve the required moisture content, to reduce fungi decay, to minimizeattack of insects, to increase strength of wood and for reduction of wood warpage Seasoningis classified into two categories namely natural seasoning and artificial seasoning. Naturalseasoning is carried out generally in air, or in water or in smoke. Air seasoning is the oldestmethod of drying timber and it depends entirely upon the free flow of air around the woodto evaporate moisture. A timber stack in a shade for air seasoning is shown in Fig. 9.1.

Shade

Timberstack

Fig. 9.1 Timber stack in a shade for air seasoning

In water seasoning, the timber balks are immersed in water for 15-20 days. Duringperiod, the flowing water drives away the sap pf wood it. Timber is then taken out and driedin open air for about a month. Water seasoning takes less time than air seasoning, but thestrength of wood is reduced. However by water seasoning, the timber is less liable to warp,crack and distort. This method of seasoning is highly suitable for seasoning green wood fullof sap. This seasoning process renders timber less liable to rot decay. In smoke seasoning,the wood is dried by using the smoke of rough burning timber and waste leaves. The smokeseasoning is used for woods in boats. Artificial seasoning is controlled by application of bothheat and humidity which enables to reduce the moisture content quickly and accurately. Afterartificial seasoning the wood becomes harder, whereas in natural seasoning the wood becomessoft. Kiln seasoning is an important type of artificial seasoning as shown in Fig. 9.2 in whichthe timber is seasoned by the use of a forced draught of warm air in which brings about arapid reduction in moisture content.

Insu la tionInsu la tion

TimberStack

Air not underpressure

Cham ber

Fig. 9.2 Timber stack in kiln seasoning

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9.5 DEFECTS IN TIMBER

Defects in timber may be broadly classified into three major categories

1 Due to abnormal growth of trees

2 Due to conversion or seasoning and

3 Due to fungi and insects.

The defects in each category are described as under.

9.5.1 Defects Due to Abnormal Growth of TreesDefects due to abnormal growth of trees are natural in nature and they are knots, stakes,twisted fiber and rind galls.

Knots are too much frequent in many trees. They break the continuity of fiber andweaken the timber. These defects may of dead or live kind. Fig. 9.3 shows a knot defect. Adead knot will come out of the wooden piece leaving a knot hole. It is produced when a branchis broken off before the tree has finished growing. A live knot occurs when a branch separatesfrom the tree after felling of the tree. Live knot will not become loose and fall out of itsposition but may tend to crack. This provides inlets for any fungi to attack the wood. If theseknots are not too large and not too near the edge of the plank, they will not present a greatproblem however dead knots in timber makes the wood unsuitable for structural use.

Knot

Fig. 9.3 Knot defect in timber

Shakes in timber are splits in the grain and often arise as a result of uneven seasoning.They may be of radial, heart, star, cup and upset kind. An upset or rupture is a shake inwhich the fracture occurs across the grain. This is thought to be caused by violet jarring ofthe timber during felling and is often found in mahogany.

Sometimes, the fibers of a tree may get twisted due to wind action in branches. Thisdefect is known as twisted fibers defect in timber. The fibers of wood have different inclinationswith its axis. They are no more parallel to the axis of the wood. Twisted fibers in timber offerdifficulty in working and a smooth surface cannot be obtained.

Rind gall is the defects due to abnormal growth of trees. It is the wound created onthe tree while a branch breaks and parts off or gets cut. Decay may occur at that point.

9.5.2 Defects Due to Conversion and SeasoningDefects due to conversion and seasoning of timber involve shakes, warping, bowing, twist, diamonding,casehardening and honey combing. Some of such important defects are discussed as under.

Warping is a kind of variation from a true or plain surface and may include a one orcombination of cup, bow, crook and twist. Warping board which is tangentially sawn mayinvariably warp. This takes the form of a hollowing or cupping across the face of the boardand when wide flat boards are required this will act as a serious drawback. Wind or twistdefect occurs when thin boards are cut from a log having curved longitudinal grain. Thistendency is for the board distort spirally.


Diamonding in timber is the tendency of square cut pieces to become diamond shapedwhen cut from certain areas of the log. This happens when the piece has been cut withgrowth rings running diagonally, causing the unequal shrinkage between summer and springgrowth to pull it out of shape.

9.5.3 Defects due to Fungi and InsectsDefects due to fungi and insects in timber involve fungi, dryrot, and wetrot which arediscussed as under.

Fungi in timber use the wood as their food and destroy the same. It acts on the woodtissues and cells and cause decay. There are two types of defects in wood because of fungi andinsects which are known as dry rot and wet rot.

Dry rot is a type of fungus on dry wood which feeds on damp wood and breaks it down.Dry rot is so called because infected wood eventually becomes lighter in weight and takes onthe appearance of being badly charred by fire, except that it is brown in color instead of blackand crumbles under slight pressure. This fungus cannot develop in wood which has a sapcontent of less than 20% so that to prevent it, all that is really necessary is to use seasonedtimber and to keep it dry.

Wet rot in timber is the decay due to dampness. The wood looks wet due to fungi attackon living trees. The effected positions of wood are reduced to a gray brown powder. Wellseasoned wood, protected by painting etc., will avoid wet rot.

Insects such as beetles, borers and white ant attack the wood and render it of no use.Beetles are commonly found in temperate region and the field of tropical and non tropicalregions. Beetles use timber as their food. Borers produce holes in the timber to find shelterfor living. White ants or termites are very common in warm temperature countries. Theyattack the wood, and make it hollow from inside. The insect attack may be controlled throughthe use of insecticides. In another method, the timbers are placed in a kiln where steam andheat are used to suffocate the pests.

9.6 TIMBER PRESERVATION

It is highly essential to protect timber from attack of fungus and any damage from insectattack. Timber products require protection if it is exposed to weather such as doors, windows,poles etc. Extending the life of the timber through preservation is a much cheaper deal. Theobject of treating timber with a preservative is to render it immune to decay, even thoughit may become quite damp and to prevent attack by timber boring insects. Most timberpreservatives belong to one of three main group tar-oil derivatives creosote, water solubletype and organic solvent chemicals.

9.7 CHARACTERISTICS OF A GOOD TIMBER

Timber is free from knots, insects attack, excessive moisture, discoloration, twisted fibers,cup and ring shake, sound, bright and free from any discoloration. It is solid with annual ringsbut not hallow in the center. Timber should be well seasoned for easily workable specific use.It should possess straight fibers and high fire resistance. It should not split when nails aredriven in it. It should not clog with the saw teeth during the sawing operation. Timber shouldbe highly suitable for polishing and painting.

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9.8 FACTORS INFLUENCING TIMBER SELECTION

The factors influencing the selection of timber involve the quality of timber in terms of itsdurability, workability, weight, hardness, cohesiveness, elasticity, type of texture, type ofgrains, resistance to fire, resistance to various stresses, ability to retain shape, suitability forpolishing and painting.

9.9 PLYWOOD AND APPLICATIONS

For the last so many years, the use of the plywood and other manufactured boards has, invarying degrees have replaced the use of solid timber in the making of furniture, fittings,paneling and many forms of constructional work. Plywood is generally made of three or moresheets of veneer glued together, with the grain of successive plys laid cross-wise. Since thestrength of timber lies along the grain, when plys of veneer are bonded in opposing graindirection, strength is distributed to both length and breadth of the piece. The plywood can beobtained in much larger sizes without shrinkage and warping in comparison to plain wood.The molded plywood boats, television and radio cabinets can be formed from plywood. Theplywood can withstand easily against humid condition. Plywood is lighter in weight andstronger across the grain than even the toughest hardwoods. Screws and nails can be drivenclose to the edge of plywood without any danger of splitting. High class surface finish can beare easily obtained on plywood.

The development of moisture and heat-resistant adhesives have contributed to the useof laminated members for heavy truss construction, to the gluing together of narrow boardsto make wider ones, and to the making of finger joints by which short lengths are joined tomake longer pieces. Plywood is used for many forms of construction, including sheathing,interior finish, sub flooring, under-roofing, paneling, flooring, cabinets, furniture, shelving,partitions, ceilings, containers such as baskets, boxes, crates, trunks into boats, toys, tables,woodenware and repair work in garages and basements.

9.10. MISCELLANEOUS MATERIAL USED IN CARPENTRY SHOP

There are a number of other materials used in carpentry shop besides timber. The mainmaterials are dowels, nails, screws, adhesives, paints and varnishes. A brief description ofsuch material is given as under.

Dowels

Dowels are wooden pieces of special nails kind generally made out from bamboos orother similar wood by the carpenter himself. They are used for fastening different woodstructural components. Hole is initially drilled through the two pieces or parts to be joinedtogether. After assembling of in proper position of the parts to be joined, the dowel is thendriven through the parts.

Nails

Nails in wood work are made out of drawn wire of brass or copper or low carbon steelor malleable iron rods. Nails made from drawn wires are termed as wire nails and areproduced from rods as clasp nails. The clasp nails possess a better holding capacity than wirenails. According to the use, the wire nails are subjected to light and medium work while theclasp nails are commonly used for heavy work. Nails are mainly used for reinforcing glued


joints and fastening different component of woods. Their size is specified by length anddiameter. These are sold by weight in the market.

Screws

Screws are made from bright drawn wires or thin rods and they are used mainly forfixing the metallic fittings like hinges and hasps in wooden structure.

Adhesives

Adhesives is defined as the sticking substance such as glue, paste, cement and mucilagethat is capable of holding wooden parts together by surface attachment permanently. It iscommonly used to join together the boards edge-to edge to form a larger surface or face-to-face to increase the thickness. It is applied on large surface areas of material as when layingveneers and is also used to stick together relatively small surface areas such as wood workingjoints. An efficient adhesive or sticking paste or glue is one that maintains good bond betweenthe wooden elements under the conditions of service that the joint has to withstand. It isrequired frequently for joining together the wooden boards edge to edge to form a largersurface or face to face to increase thickness in joinery work and many other common typesof wood works. It is applied either cold or hot condition. The former is known as liquid orcold glue and is used when a slow and less strong setting is desired. When applied hot, it isknown as cooked glue that enables a very strong and permanent type of joint between theadjacent layers of wood pieces. Few commercially available adhesives can be classified ascasein glue, animal glue, vegetable glue, albumen glue, synthetic resins, poly-vinyl-acetate(PVA), paint and varnishes, rubber cement and plastic cement and few important such adhesivesare briefly discussed as under.

Casein glue

Casein glue is made by adding an alkali to the curd of skimmed milk. It is commerciallyavailable in powdered form in the market. It can be made into a paste, while using, by addingwater. It is thicker than animal glue but squeezes out of the joint quickly when pressed. Thisglue requires 15 to 20 minutes to set a wooden joint and therefore thus provides the carpentersufficient time to glue and clamp his work. Casein glue is a commonly used adhesive whichis very strong and water resistant. It is used specially in components which are continuouslysubjected to high humidity viz. furniture, boat making, veneering, beams and others woodencomponents.

Animal glue

This glue is made from hides, hoofs, bones and other waste parts of animals. Thesematerials are refined and developed in form of sheets, flakes or powder. Before applying, theglue should be soaked in cold water over night and then heated. It is generally applied hotand sets very rapidly. It is also available in liquid form commercially which is applied cold i.e.it does not require any heating before application. An important point is to be noted that thisglue should be applied immediately after heating. Repeated heatings should be avoided as thisweakens the bond of the glue and also its fluidity is lost due to evaporation of water,rendering it thicker.

Vegetable glue

It is developed from the starch which is obtained from roots, grains and corns of treesby subjecting them with acid and by grinding to a powered form. It is mainly used in plywoodwork and it is not much suitable for general work

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Albumen glue

It is prepared by adding an alkali to beef blood and is available in flakes forms in themarket. During use they are dissolved in water in about an hour earlier, to found a liquidsolution and it gives a very strong and water proof bond.

Synthetic resin glue

This glue is made from formaldehyde uric acid and other chemicals. It is available ingenerally powder form. Before use, it is thoroughly mixed with water to proper consistency.The commercial varieties of resin glue involve polyvinyl-resin glue in liquid form, plastic resinglue in powder form and resorcinol-resin. The polyvinyl glue is the fastest setting, strong,easy to use and it is extensively used in furniture and decorative work. The plastic resin glueis mainly used in plywood work. The resorcinol glue can be used for joining wooden partswhich are constantly subjected to changing weather condition exposed to humid environment.

Paint and varnishes

They are commonly applied on wooden or metallic articles for the reasons to protectingthe surfaces of wood or metal from the effects of moisture and weather change. They are usedon surfaces for making them decorative in appearance.

9.11 CONSTITUENTS OF AN OIL PAINT

A good paint must have sufficient fluidity so that it can be easily spread by a brush over thesurface. It should form a durable and wear-resistant film on drying over the surface of wood.It should retain its color on drying and under changing conditions of atmosphere and shouldnot be affected much by moisture. It should give a pleasing appearance to the surface ondrying. An oil paint comprises of various constituents such as base, vehicle, pigments, thinnerand driver which are discussed as under.

Base is a major constituent of oil paint. It is finely ground powdered material which ismixed and then applied to the surface of the finished part to form the body of the paint. Thefunctions of a paint base is to provide a sort of reinforcement to the film coated on the surfaceof finished parts after it dries, in order to make it hard and wear-resistant for long life. Italso minimizes the chances of cracking of the coated film of paint after drying. Commonlyused bases involve white lead, red lead and iron oxide.

The second constituent named as vehicle will act as a binder for the solid material andenables suspension of base and other coloring pigments in order to allow their even applicationon the prepared surface of the products and it facilitate its adherence to the latter. The wellknown vehicles are raw linseed oil, single or double boiled linseed oil, refined linseed oil, nutoil, stand oil and poppy oil.

The third constituent of oil paint function is pigments which provide various colors tothe paints. They are generally available in fine powdered form and the best one is which doesnot change its color even on being exposed to sun and heat. The black color oriented commonpigments are graphite, lamp black, and vegetable black. The blue color oriented commonpigments involve Prussian blue, cobalt blue, indigo. The green color oriented common pigmentsis chrome green. The red color oriented common pigments are Indian red, red lead, vermilion,and venetian red. The brown color oriented common pigments are raw umber, burnt umber,raw sienna, burnt sienna. The black color oriented common pigments are chrome yellow andyellow achre.


The Thinner is a such a solvent which, when added to the paint, reduces its consistencyand, thus, enhances its flow ability thereby facilitating an easy and quick spreading of paintover the surface of the job in the from of an uniform thin film. It is important to note thatthe thinner should not be added to the paint in an excessive quantity. The amount of athinner in paint varies between 5 to 8 percent of the paint. The commonly used thinners areturpentine and naphtha.

The main objective or function of a drier in oil paint is to increase the rate of dryingof the vehicles and hence the applied paints. The generally used driers are red lead, zincsulphate, lead acetate, lead oxide and manganese sulphate.

9.12 COMMON TOOLS USED IN CARPENTARY SHOP

Commonly used tools to shape wood for various types of joints by driving in and driving outnail involve cutting and smoothening of wood surfaces. A broad classification of tools used inthe wood working or carpentry shop are measuring and marking tools, supporting and holdingtools, cutting tools, striking tools and miscellaneous tools. Most of commonly used tool andmeasuring devices as mentioned above are in chapter of fitting and sheet metal work also.Other some important such tools and instruments are discussed as under.

9.12.1 Marking and Measuring ToolsMarking in order to make wooden components of the required size or the marking of exactdimensions on the wooden piece is essential to produce quality jobs. A number of markingand measuring instruments namely Rules, Try Square, Combination Set, Bevel Gauge, MarkingGauge, Mortise Gauge, Cutting Gauge, Spirit Level, Trammel and Compass are commonlyused for this purpose. Some of commonly used marking and measuring instruments arediscussed as in chapter of fitting and sheet metal work under.

Rules

Rules are straight edge of wood or steel engraved in millimeters- centimeters or ininches-foot or in both. Theses are used to mark, measure the length, widths and thicknessesof wood part. Figs. 9.4.-9.6 show steel rule, folding rule and flexible steel rule. These rulesare available in different sizes and designs. Metallic taps bearing sizes 6", 12" or 18" are usedfor general measuring work. For example 24" folding tape and 5" or 6" steel tape are usedmeasuring larger dimensions. An important small instrument in any shop is a good qualitystraight-edge bench rules. These rules are manufactured of either metal or wood. They areused to check for straightness and to measure and mark straight lines. The bench rule maybe graduated in inches, millimeters or both. The length of the bench rule may be 12", 24"or 36". The 36" rule is called yardstick. Another type of rule is folding two-foot rule which ismore convenient than a straight 24" rule. The zigzag rules are used to measure longer stockwhen exact measurements are not so important. One of These rules, when open may be ofusually 6 or 8 feet long. The push pull steel tape or tape rule is a very compact metal rulethat comes in lengths of 6, 8 or 10 feet. There is a hook at the end to slip over the edge ofthe bold. It is flexible to bends easily and can measure curved surfaces too. It is very goodfor measuring the inside depth of the hole of components also.

Try Square

Try square is generally utilized for measuring and checking of squareness, perpendicularity,dimensions, testing of finish of planned surfaces and drawing parallel and perpendicular lines.

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The steel blade and metallic or wooden handle of try square are at right angles to each other.Try square is used for testing the level, edge and square ness of the wooden surfaces. It isalso used for marking lines across the face or edge of wooden block. There are graduationsalong the blade of the rule that are used for measuring and marking purposes on the woodenjobs. The blade of try square is made of hard tempered steel of non rusting kind. It is seldomused for hammering work.

1 2 3 4 5 6

Fig. 9.4 Steel rule

31 32 33 34 35 36 37 38 39 40

1718192021222324252627282930

Fig. 9.5 Folding rule

1 2 3 4 5 6

Scale

Fig. 9.6 Flexible steel rule

Combination Set

Combination set is frequently used in the carpentry shop for different kind ofmeasurements. It consists of blade and a head. The blade has a groove cut along its lengthso that it can slide into the head. One side of the head makes a 90° angle with the blade andthe other side a 45° angle. It can be making, measuring and setting different angle. It alsoacts as a try square, angle gauge to set 45° angles, a depth gauge and level checking tool.

Bevel Gauge

Bevel gauge is also known as an adjustable bevel which is mainly used for marking,measuring and inspecting angles from 0 to 180 degree. Its blade can be adjusted and set toany desired angle.

Marking Gauge

The marking gauge is made of wood which is important tool utilized to make lines ata uniform distance from the edge of a board or piece of work and is used principally whenpreparing wooden components to size before jointing. The marking gauge like the mortisegauge and cutting gauge in use should be positioned correctly. For marking purposes, thegauge is drawn towards the body or pushed away from it but in either case, if the spur doesnot trail. It will tend to jump and run with the grain. Thumb screw of the marking gaugelocks the stock at any position. The spur made of hardened steel should be ground to a finepoint. And for ease of working, it should not project too far from the face of the stem. It is


commonly used to mark or scribe line parallel to and at any desired distance from a finishededge or face of a surface

Cutting Gauge

Cutting gauge is similar in construction to the marking gauge but having a knife in placeof the marking pin or spur. It can be utilized for gauging and marking deep lines across thegrain of wood in thicker sections. It is also used for setting out the shoulder-lines of lapdovetails and similar joints, as well as for trimming veneers parallel to the edge of surfacebefore laying a cross-band. Cross banding is the laying of a strip of cross-grained veneeraround the edge of a surface for example the edges of a table top, box lid or drawer front.This gauge is very useful for making very small rebates to receive inlay lines and may beused in place of marking gauge. Inlay lines are thin strips of wood which can be glued intoa rebate cut around the edge of a veneered surface.

Mortise Gauge

9.7 shows a mortise gauge. This is an improved form of marking gauge which consistsof main components as fixed pin, sliding pin, brass strip, stem, rose wood stock and thumbscrew. The fixed pin of the gauge is attached to a short brass strip which is screwed to thestem. The sliding pin is fixed to a long brass strip or slider is adjusted by means of athumbscrew. The threaded portion of which engages in a cylindrical nut which is embeddedin the stem. The stock is locked in position by a metal set screw. This gauge is used formarking out of the parallel sides of a mortises or tenons and other similar joints.

FixedPin

Slid ingPin Stock G roove

Screw

Fig. 9.7 Mortise gauge

9.12.2 Holding And Supporting ToolsSometimes it is desirable to support and gold a wooden board in a special manner while thework is being carried out. For these purposes, various supporting and holding devices areneeded some of which are discussed as under.

Work Bench

Every carpenter generally needs a good solid bench or table of rigid construction of hardwood on which he can perform or carry out the carpentry operations. Work bench should beequipped with a vice for holding the work and with slots and holes for keeping the commonhand tools. One jaw of the vice is tightened to the table and is kept moveable for holding thearticles Work benches are built solidly with good heavy tops for providing a good workingsurface for cutting, as well. The vice on the bench is equipped with an adjustable dog thatis, a piece of wood or metal can be moved up and down in the outside jaw of the vice.

Carpenter Vice

Carpenter vice (Fig. 9.8) is very important tool in wood working shops for holdingwooden jobs. There are several varieties of vices, each possessing its own particular merit.

Carpentry 165

Jaw

Trigger for qu ick opening

Fig. 9.8 Carpenter vice

Clamp

Clamps are commonly used in pairs in gluing up operations at the final assembly of woodjoinery work. These clamps can provide pressure required to hold joints together until theyare secured due to the setting of glues. Clamps are of two types namely plain rectangular bartype and T-bar type. The former is made of mild steel and is usually rectangular in section.The later may be of T-section, which can easily afford greater rigidity under stress. Thecoarse adjustment jaw may be located in any position on the bar by means of a steel pin whichfits into any of the holes drilled at intervals along the bar. The fine adjustment jaw of thesash clamp is moved along the bar by a square threads screw which passes through a specialnut fixed to the end of bar. Considerable pressure can be applied by turning the screw withthe Tommy bar for holding a wooden job. Both jaws of the sash clamp are generally madeof malleable cast iron which is tougher and less brittle than ordinary cast iron. There areother similar types of such clamps named as rack clamp, screw clamps, light duty parallelclamp, adjustable bar clamp (Fig. 9.9), G or C-clamp (Fig. 9.10), and double bar clamp whichare useful for holding different sizes and shapes of wooden jobs.

Hand lePin

Ho le T-bar

JawsHeadScrew

Base

JawsScrew

W ingnutBody

Job

Fig. 9.9 Bar clmap Fig. 9.10 G or C-clamp

9.12.3 Cutting ToolsVarious kinds of cutting tools namely various kinds of saws, planes, chisels, scraper, files, andrasp adze and axe and boring tools such as brace and bits, bradawl, auger, gimlet are usedin the carpentry shop. Few important types of cutting tools are described as under.

9.12.3.1 Saws

Saws are wood cutting tools having handle and a thin steel blade with small sharp teethalong the edge. They are utilized to cut wood to different sizes and shapes used for makingthe wooden joints that hold parts together. They can be further classified into three majortypes namely hand Saws (Rip, Cross-cut, Panel, Keyhole and, Pad saw), Snuff Saws (Tenon


and Dovetail) and Frame Saws (Coping, Bow and Fret). Few important types of saws areshown in Fig. 9.11. Some of them are described as under.

Rip Saw

The rip saw is shown in Fig. 9.11. It is used for cutting timber along the grains. The teethof rip saw are chisel-shaped and are set alternately to the right and left. A 24" long point sawis a good for sawing work. Depending upon whether the saw is designed to rip or cross-cut, theshape of the teeth will also vary. In the case of a ripsaw, the teeth are shaped like chisels.

Stee l b lade W oodenhandle

R ip S awR ip S aw Teeth

Cross cu t Handsaw

Cross cu t and panel teeth

Pane l Saw

Peg tee th fo r dovetailand tenon saws

Doveta il Saw

Tenon or back saw

Coping Saw

Compass saw

Bow saw

Fig. 9.11 Few important types of saws

Carpentry 167

Crosscut Saw

Cross cut saw is shown in Fig. 9.11 which is similar to rip saw in shape. It is primarilydesigned for cutting across the grains of wood. The teeth are knife shaped and bent alternatelyto the right and left for making the saw to cut wider than the blade. The saw cut is calledthe kerf. Since the kerf is wider than the blade, the blade will not stick as the sawing is done.The saw teeth may be coarse (with only 4 or 5 teeth per inch) or fine (with ten or twelveteeth per inch). A jaw for general purpose cutting should have about eight or nine points perinch (there is one more point than teeth per inch) and should be about 24 inches long.

Turning Saw

The turning saw is similar to the copying saw which is designed for cutting curves,scrolls and roundings on wooden jobs. It is used chiefly on heavier work where long faststroke and less accuracy of cutting are required. The thin blade of the turning saw isremovable. This saw can be pivoted between the handles. The saw generally cuts in thepulling stroke.

Dovetail Saw

Dovetail saw is shown in Fig. 9.11 which is little and is closely similar as related to thebacksaw or tennon saw. It is lighter and however possesses a thinner blade and finer teeth.The handle is round, to provide a delicate grip for fine cutting. This saw is used whereabsolutely finer and delicate cutting is required in wood work.

Compass Saw

Compass saw carries a tapered blade which is long as shown in Fig. 9.11 which is oneof the special saw having thin, narrow and flexible blade. With a blade resembling the beakof a swordfish, this type of saw is commonly used for making cutouts on the inside surfaceof a piece of work. A hole is first bored inside the portion which is to be cut out and thepointed compass saw is pushed into the hole to start the sawing operation. Its blade containsabout 12 teeth per cm length

Keyhole Saw

The keyhole saw is used in the same manner as the compass saw. For this reason it isgenerally employed for fine internal and intricate work where the compass saw would be toobig and clumsy for the carpentry job.

Hacksaw

Hacksaw is shown in Fig. 9.12 which consists of steel frame and a hacksaw blade. Whileessentially designed for cutting metal, this tool comes in for a variety of uses in the woodworking shop. The frame of hacksaw is designed in different ways, some with pistol grips,others with handles similar to those used on a conventional saw and others with turnedhandles. Blades of hacksaw are detachable and can be obtained with teeth of varying coarseness.

Hand le

Stee l fram e

LeverHSS B lade

W ing nut

Fig. 9.12 Hacksaw


9.12.3.2 Planes

A plane is a special tool with a cutting blade for smoothing and removing wood asshavings. It is just like a chisel fixed in a wooden or steel body. Fig. 9.13 shows a simpleplane. The modern plane has been developed from the chisel. They can also be classified asjack plane, smooth plane, jointer plane, trying plane, rabbit plane, circular plane and foreplane. Few important planes are discussed as under.

Bolt

W edgeThroatStrik ing

Bottom

Heel

Hand le

BladeM outhToe Block So le

Fig. 9.13 Simple plane

Jack Plane

Jack plane is most commonly used plane which is shown in Fig. 9.14 which comprisesof its body about 40 cm long, blade 5-6 cm wide and handle. It is good for rough surfaces thatrequire a heavier chip. It is ideal for obtaining a smooth and flat surface. There are actuallyforty-six different parts of jack plane, the carpenter needs only acquainted with the workingor regulating parts. The main working parts are the cutting blade or plane iron. The adjustingnut is operated to raise or lower the blade and the adjusting lever which regulates the bladeso as to make possible an even or slanted cut. The cutting blade of the jack plane is guardedwith a metal cap which is adjusted on top of the blade to within about 2.4 mm of the cuttingedge. The metal cap of the jack plane eases the cutting action by curling and breaking off thewood shavings evenly, thus preventing splitting or splintering of the wooden part.

Str ik ingButton

W edge Blade

Hand le

Fig. 9.14 Jack plane

Smoothing Plane

Smoothing plane is shown in Fig. 9.15 which is somewhatsmaller than the jack plane, measuring between 6 and 10 inchesin length. It is a fine utility tool, especially useful for planning endgrain, chamfering, and other edge shaping of wooden part. Thisplane is also used for cleaning up after gluing and assembly, butowing to its short length should not be used for producing verytrue surfaces.

Blade

Fig. 9.15 Smoothing plane

Carpentry 169

Jointer Plane

When a fairly long board is to be planed absolutely straight and square along the edge,it is easier to obtain a straight and level surface with the jointer plane in comparison to anyother type of plane. This plane is made up in various sizes but the most popular type of jointerplane is 24 inches in teeth.

Trying Plane

The wooden trying plane is shown in Fig.9.16 which is similar in construction to thejack plane except that its blade is wider andmuch longer than jack plane. Its mouth is alsonarrower than that of the jack plane.

Rabbet Plane

Rabbet plane is shown in Fig. 9.17 whichis used for sinking one surface below anotherand shouldering one piece into another. If theedge of a piece of wooden board is to berabbeted, this plane is being generally used.The side guide and the cutting blade of therabbit plane may be adjusted so as to cut rabbetsof varying widths and depths. The plane isuseful for various types of edge shaping. Rebateor rabbet means a recess or step cut into theedge or end of a wooden board.

Circular Plane

The shape of circular plane adapts it for planning either convex or concave surfaces andfor shaping round edges. This plane may be adjusted so that the flexible bed will conform tocircles of various sizes.

Fore Plane

This plane may be said as a junior jointer plane. It is slightlyshorter than the conventional jointer plane. It is mainly used forplanning edges of medium length.

9.12.3.3. Chisels

A Chisel (Fig. 9.18) is a strong sharp edge cutting tool with asharp bevel edge at one end. Its construction is composed of handle,tang, ferrule, shoulder, and blade. Chisels are generally made up ofhigh carbon steel. They are used to shape and fit parts as requiredin joint making.

A gouge (Fig. 9.19) is a curved chisel. It may be outside or insideground. Outside ground gouges are called firmer gouges and insideground gouges are called scribing gouges. The scribing gouges aremade long and thin, they are known as paring gouges. Several varieties

Fig. 9.16 Trying plane

Fig. 9.17 Rabbet plane

Hand le

Farru l

Tang

Shank

Blade

Fig. 9.18 Chisel


of chisels are available, each having special characteristics which fit it for its special use.There are two types of construction employed in the making of chisels named as tang andsocket types. The tang chisel is made with a ranged or pointed end which pierces into thehandle. The socket chisel reverses the process by having the handle fit into the socket collaron the blade.

Hand le

InsideO nside

Fig. 9.19 Gouge

Firmer Chisel

Firmer chisel is shown in Fig. 9.20 which possesses a blade of rectangular section. Itconsists of the following parts blade made of cast tool steel and it is used for general benchwork. The shoulder of the chisel prevents the tang from being driven farther into the handlewhen the chisel is struck with a mallet. The ferrule is short length of brass tube (mild steeltube in the case of some mortise chisels) which fits tightly over the lower end of the handle,and helps to prevent its splitting by the tang. The tang is not hardened as to fit in the handle.The handles turned from ash or beech wood as these timbers are resistant to splitting.

20° To 25°

Cutting blad eHand le

Fig. 9.20 Firmer chisel

Beveled edge firmer chisel

Beveled edge firmer chisel (Fig. 9.21) is identical to the firmer chisel except that theedges of the back of the blade are beveled. This enables the chisel to be used for cutting rightinto the corner of acute-angled wood work such as the base of a dovetail.

Fig. 9.21 Beveled edge firmer chisel

Paring Chisel

Paring chisel (Fig. 9.22) has a longer and usually slightly thinner blade than firmerchisel. It may be obtained with a blade of rectangular or beveled edge section and is used in

Carpentry 171

pattern making and where long accurate paring is required. The paring chisel should not bestruck with a mallet. This chisel is intended for manipulation by hand only, and not fordriving with a mallet like a firmer chisel for cutting of wooden jobs.

Fig. 9.22 Paring chisel

Mortise Chisel

Mortise chisel (Fig. 9.23) is designed for heavy work. A mortise chisel has a blade whichis very nearly square in section and so may be used as a lever for removing chips and willwithstand heavy blows from a mallet. Various types of handles are fitted to mortise chiseldepending upon use. Mortise chisel has an oval beech handle, whilst the heaviest type of allhas a socket handle. This socket replaces the ferrule and affords greater resistance to splittingwhen used for very heavy work. The leather washer acts as a shock absorber.

Hand leCutting Edge

Fig. 9.23 Mortise chisel

9.12.3.4. Scraper

The scraper for wooden work is used in carpentry shop. It is used after planning to obtaina smooth surface before final glass papering. Where the grain in wood is particularly twistyso that even a finely set plane tends to tear it, a sharp scraper will be found most useful totackle this problem. It is also used for cleaning up veneered work as its curved edges are usedfor cleaning up large molding of concave section and other similar work. The scraper is heldas the thumbs being positioned low down and pushed forward to curve the blade so that thecenter of the edge rather than the outer corners comes into contact with the surface of thewood. A sharp scraper will produce fine shavings on wooden surfaces.

9.12.3.5. Files and Rasps

Files and Rasps are shown in Fig. 9.24. They are of used for maintaining other woodworking tools and equipment. They are made of hardened tool steel which is tempered andthey should never be dropped as they are very brittle to break. They are of various typesdepending upon their size, shape, cuts and degree of their coarseness.

Hand leTangBlade

Fig. 9.24 Rasps

9.12.3.6. Adze

An adze (Fig. 9.25) is used for rough cutting, squaring, tochop inside curves and to produce concave surfaces. Its outerface is convex, inner face concave and edge is beveled to forma cutting edge. It is made of carbon steel.

Head

Hand le

Fig. 9.25 Adze


9.12.3.7. Axe

An axe is used for splitting the logs and for removing bark from the wood. It is madeof carbon steel and both sides are beveled to form a cutting edge. Its one side is plane andthe other is beveled to form a cutting edge. It is used to make the surface roughly plane.

9.12.3.8. Boring Tools

Boring is cutting a hole in wood with a tool called a bit. Holes of 6 mm size or largerare bored. Holes of 6 mm size or smaller are drilled. Boring is the first step in making anykind of shaped opening or making holes. The commonly used boring tools bits are discussedas under.

The center bit

The center bits (Fig. 9.26) are available in sizes ranging .from 4 mm to 50 mm and areuseful for boring holes through thin wood. They are not recommended for deep boring as ithas a tendency to wander or drift as a result of varying grain texture and direction in wood.The screwed center of the improved center bit helps to draw the bit into the wood andtherefore requires less pressure to obtain a cutting action.

Fig. 9.26 Centre bit

Auger bits

The auger bits (Fig. 9.27) are also known as twist bit. They are the most commonly usedhole making tools used in wooden wood. They may possess a single twist auger bit or adouble-twist auger bit. These bits are more costly than center bits. They can produce holeseasily and accurately from 5mm to 35 mm in diameter in wooden jobs. The hollow featuresare important in both types of auger bits, because the parallel sides of the bit help to preventdrifting. And the twisted form of the body of the bit helps in the removal of cuttings. Boththese bits have two cutters and two spurs as well as a screw center for quick and clean boringaction in wood work.

Fig. 9.27 Auger bit

Countersink bits

Countersink bit (Fig. 9.28) is used for countersinkingthe predrilled holes to placement of heads of screws.

Shell and spoon bit

Shell and spoon bits are the traditional kinds of bit whichare now superseded by the carpenter’s twist drills or bits.

Expanding bits

These are commonly used forms of screw center bit which are adjustable for cuttingholes of from 15 mm to 75 mm in diameter. The two combined cutter-spurs are provided ineach case to cover the range of hole sizes.

Fig. 9.28 Countersink bit

Carpentry 173

Forstner bits

These are used for boring clean sided stopped holes of flat bottom kind.

Snail bits

The snail bits have only one cutter which gives a clean cutting action.

Rose bits

The rose bit tends to scrape rather than cut. It is generally used on soft metals inaddition to wood.

Bradawl

Bradawl is used for making fine holes, especially nail holes in soft woods. The cuttingedge of the blade, which is sharpened equally from both sides, is placed across the grain sothat the wood fibers are severed and not merely forced outwards. The blade is forced into thewood and it is then allowed to twist for enlargement of the diameter of the hole being boredand then finally removed. The cutting edge of the blade of bradawl is flared out to giveclearance to the body of the blade which is fixed to the handle by means of a square-taperedtang. A brass ferrule is fitted to prevent the tapered tang splitting the handle when beingpushed into it. The blade of bradawl is shouldered to prevent its being forced further into thepear-shaped handle which is usually turned from ash, box or wood.

Auger

The auger (Fig. 9.29) is a carpentry hand tool (made upof steel bar) and is used to make holes in the wooden jobs. Itpossesses a screw point to center the tool at the point wherehole is to be produced in the wooden part. Fluted body of theauger is to allow removal of wooden chips from wooden jobsusing handle to apply pressure to rotate the auger for makingthe hole. Holes up to 25 mm diameter can be produced.

9.12.4 Striking toolsMallets and various types of hammers are generally used asstriking tools in carpentry shop. A hammer delivers a sharp blow,its steel face being likely to damage the chisel handle whereasthe softer striking surface such as mallet will give better result.Some of important such tools are discussed as under.

Mallet

A mallet is a short handled wooden hammer with a large head as shown in Fig. 9.30.It is used to strike a chisel for heavy cutting waste wood, from joints such as mortises andhalving joints and also for removing unwanted, wood on shaped work etc. Mallet is frequentlyalso used to tap parts of a project together during the assembly process.

Head

Hand le

Fig. 9.30 Mallet

Hand le

Flutes

Screw Po in t

Fig. 9.29 Auger


Hammers

Warrington, peen and claw hammers are generally used by carpenters. They are describedas under.

Warrington Hammer

Warrington hammer (Fig. 9.31) is used for knockingin nails, assembling joints and setting wooden plane blades.The head is forged from tool steel and is obtainable invarious weights. The face of hammer is hardened, temperedand ground slightly convex. The center part of the head isnot hardened as a precaution against breakage in usethrough its being to brittle. The handle is made of woodand is oval in cross-section to have a comfortable grip. Theend of the handle fits into a hole in the head and is held in position by wooden or metalwedges which open out the grain, thus securely locking the two parts together.

Peen Hammer

The peen hammer is used for striking nails where the use of the face is impracticable.The peen hammer is very light and is used for driving the panel pins and fine nails.

Claw Hammer

The claw hammer is shown in Fig. 9.32. One of itsend possesses curved claw which is used for extractingnails in order to provide the extra strength needed forthis levering action. The other end is used for lightstriking work. A strong handle on claw hammer isalways necessary for carrying out the task.

9.12.5 Miscellaneous ToolsOther some miscellaneous carpentry hand tools that are also used in carpentry shop includescrew driver, pincer and fasteners which are discussed as under.

Screw Driver

Screw driver (Fig. 9.33) is used to drive the screws into the wood. The tip of screw drivershould be slightly hollow-ground so that it will fit accurately in the slot in the screw-head.The blade of a screwdriver is made of hardened tempered tool steel so that its tip canwithstand the great strain put upon it while screwing. The tang of screw driver is nothardened. It is wide and rectangular in section so that it will restrict the twisting action putupon it during use. The ferrule is slotted to receive the tang and to hold it firmly in placein the handle. The handle, if made of wood, is usually pear-shaped or if made of unbreakableplastic, is generally of a fluted cylindrical shape. Some screwdrivers are fitted with a ratchetdevice used for clockwise anti-clockwise turning.

Hand leFarru l

B ladeTip

Fig. 9.33 Screw driver

HeadC law

Hand le

Face

Fig. 9.32 Claw hammer

Cross Peen

Hand le Head

W edge

Fig. 9.31 Warrington hammer

Carpentry 175

Pincer

Pincers are commonly used for withdrawing nails. They are made of cast steel, the jawsbeing hardened. The end of one of the arms is shaped to form a claw for removing nails. Thenail head is firmly gripped between the jaws as the long arms permit considerable pressureto be exerted by them. The nail is extracted from the wooden body by a leveling action, usingthe curved side of one of the jaws as a fulcrum. A small block of wood placed between thesteel jaw and the work prevents damage to the surface of the wood.

Various types and sizes of screws are available in different sizes from 6 mm to 150 mmand are sold in market by numbers. A hole is drilled before putting the screw and then sameis driven into former by means of a screw driver.

Bolts and nuts are used only where very heavy components are to be fastened togetherviz., wooden roof trusses and folding type furniture etc. The standard B.S.W. mild steel boltsand nuts are used.

9.13 COMMON WOOD JOINTS

All wooden objects whether doors, windows, furniture, pattern, core boxes, handicrafts, toys,cots, etc., are all assembled with joints. The various common used wood working joints aregiven through Fig. 9.34 to Fig. 9.41.

G roove

Tongue

A

B

A

B

Fig. 9.34 Groove and tongue joint Fig. 9.35 Mortise and tennon joint

A A

B

BBB

A

A

Fig. 9.36 T-lap joint Fig. 9.37 Open or through dove-tail joint


A

A

B

B

Fig. 9.38 Cross-lap joint Fig. 9.39 Corner-lap joint

AB

AB

Doveta il

A

B

Fig. 9.40 Dovetail joint Fig. 9.41 Briddle joint

9.14 CARPENTRY MACHINES

Wood working machines are employed for large production work. These possess the followingadvantages over the hand tools.

1. The carpentry machines help to reduce fatigue of carpenter.

2. The carpentry machines are used for production work.

3. The carpentry machines save time and are used for accuracy work.

4. They are used for variable job variety and more designs are possible.

Different machines are needed to save time and labor in carpentry work for variousquick wood working operations especially for turning and sawing purposes. The general woodworking machines are wood working lathe, circular saw and band saw. These machines arediscussed as under.

1. Wood Working Lathe

A general wood working lathe isshown in Fig. 9.42 which resemblesroughly to an engine lathe. It consistsof a cast iron bed, a headstock, tailstock,tool rest, live and dead centers anddrawing mechanisms. The long woodencylindrical jobs are held and rotatedbetween the two centers. The tool isthen fed against the job and the roundsymmetrical shape on the jobs isproduced. Scrapping tool and turninggauge are generally used as a turningtool on a woodworking lathe.

Too lPost

Too lRest

Bed

Too l P ostC lam p

Leg

Face P la te

Spur Centre

Speed ChangePulleys

HandW heel

Too l RestC lam p

Fig. 9.42 Wood turning lathe

A

B

A

B

Carpentry 177

2. Circular Saw

A circular saw is shown in Fig. 9.43. It is alsocalled as table or bench saw which is used to performvarious operations such as grooving, rebating,chamfering etc. It consists of a cast iron table, a circularcutting blade, cut off guides, main motor, saw guide,elevating hand wheel, tilting hand wheel etc. The workis held on the table and moved against the circular sawto perform the quick and automatic sawing operationand other operation on wood as said above. Theprincipal parts include the frame, arbor, table, blade,guides for taking cuts, guards and fencing.

3. Band Saw

Band saw is shown in Fig. 9.44 which generally used to cut the heavy logs to requiredlengths, cutting fine straight line and curved work. It consists of a heavy cast bed, which actsas a support for the whole machine, a column, two wheel pulleys, one at the top and otherat the bottom, an endless saw blade band, a smooth steel table and guide assembly. It ismanufactured in many sizes ranging from little bench saw to a larger band saw mill.

AdjustingScrew Head

UpperPu lley

B lade

Tab le

BedLowerPu lley

Fig. 9.44 Band saw

9.15 COMMON SAFETY IN CARPENTRY SHOP

There are some general safety precautions to be taken care of while working in carpentryshop. Some of which are discussed as under.

1 Before starting any wood working machine, it should be ensured that all the safetyguards are in proper places and secured well.

2 While working on a circular saw, one should not stand in a line with the plane ofthe rotating blade and always keep your fingers always away from the reach ofblade.

3 The wooden pieces should not be fed to the sawing machines faster than the cuttingspeed of the machine.

Tab le

Cutte r

Leg

Fig. 9.43 Circular saw


4 While working on wood lathes, the job should be properly held.

5 One should not use defective or damaged carpentry tools while carrying out carpentrywork.

6 Nails, screws should be properly kept in a box for proper house keeping.

7 Sufficient safety precautions are to be taken for preventing fire in the carpentryshop.

8 No carpentry tools should be thrown for saving time in handling.

9.16 QUESTIONS1. What is the difference between hard and soft wood?

2. Describe the various methods of seasoning of timber.

3. Define exogenous trees and endogenous trees.

4. What is the difference between wood and timber?

5. Describe the various methods of conversion of timber.

6. What are the characteristics of a good timber?

7. Sketch the cross-section of an exogenous tree. Discuss the various parts of this tree.

8. Explain in brief the various defects in timber.

9. Describe a few methods of preservation of timber in brief, and why is it necessary?

10. What are the commercial sizes in which the timber is sold in the market?

11. Explain in brief with neat sketches the various types of measuring tools used in carpentryshop.

12. Discuss briefly with neat sketches the various types of cutting tools used in carpentry shop.

13. Discuss briefly the setting and sharpening of a carpentry tool.

14. Discuss briefly the various boring tools used in a carpentry tool.

15. Discuss briefly with neat sketches the various planning and striking tools.

16. Sketch the various wood working joints.

17. Explain the following carpentry processes in brief.

(i) Marking (ii) Sawing, (iii) Planning

(iv) Boring, (v) Grooving, (vi) Chiseling

18. Explain the following wood working machines in brief.

(i) Wooden lathe, (ii) Circular saw

(iii) Band saw, (iv) Planer

19. What are the general safety measures used in carpentry shop?

Documents

Crpentary+Fitting