WORKSHOP PRACTICE IILECTURE NOTES

BYJean de Dieu IYAKAREMYE (Msc)

Email: iyakjdd@gmail.comUniversity of Rwanda

AGM 204 WORKSHOP PRACTICE AND APPLICATIONS

• Component Name: Workshop Practice II Part 1: Drilling operationPart 2: Welding ProcessesPart 3: Lathe machine

Workshop Practice II

Part I. Drilling operation

1. Introduction

• Drilling is a process of producing round holes in a solid material or enlarging existing holes with the use of multi-tooth cutting tools called drills or drill bits.

• The hole is produced by axially feeding the rotating drill into the workpiece which is held on the table of the drilling machine.

• The most common widely employed drilling tool is the twist drill.

2. Types of holes

• Drilled holes can be either through holes or blind holes (see Figure 1 on the next slide).

• A through holes is made when a drill exits the opposite side of the work; in blind hole the drill does not exit on the other side of the workpiece.

• Two types of holes: (a) through hole and (b) blind hole

3. Drilling machines - Drill press

3.1. Types of Drilling Machines

• The sensitive or bench drill is used for light drilling on small parts.

• The upright drill press is used for heavy duty drilling and finally the radial drill press is used for drilling large, heavy work piece that are difficult to move.

• Sensitive or Bench drill press

• Upright drill press

Radial drill Press

• This is the largest drill press designed to drill up to 100-mm diameter holes in large workparts.

• It has a radial arm along which the drilling head can be moved and clamped.

Other drilling machines• The gang drill is a drill press consisting of a series

of drill presses connected together in an in-line arrangement so that a series of drilling operations can be done in sequence.

• In the multiple-spindle drill, several drill spindles are connected together to drill multiple holes simultaneously into the workpart.

• Numerical control drill presses (CNC)are available to control the positioning of the holes in the workparts.

4. Geometry of twist drill

• The twist drill is the most used cutting tools in the drilling operation.

Figure : Standard geometry of a twist drill

• The twist drill is the most used cutting tools in the drilling operation.

• The twist drill is provided with two spiral grooves and two cutting edges.

• The chips produced are guided up through these spiral grooves.

• The grooves also serve as passage to the cutting fluid.

• In order that the cutting edges can cut off chips, two movements are required simultaneously; rotational speed and axial feed.

• The typical helix angle of a general purpose twist drill is 18~30o while the point angle (which equals two times the major cutting edge angle) for the same drill is 118o.

• Some standard drill types are, straight shank: this type has a cylindrical shank and is

held in a chuck; taper shank: his type is held directly in the drilling

machine spindle.• Drills are normally made of HSS but carbide-tipped drills,

and drills with mechanically attached carbide inserts are commonly used in many operations, especially on CNC drilling machines.

Cutting Drill angles • In twist drill, there are various angles to be considered: Cutting angle (ca) or angle of lip:

The two lips must be of same length and equal angle. For ordinary work, the cutting angle is 59º and vary with metal to metal.

Lip clearance angle:The cone shaped cutting end is the point from the lips and varies from 12- 15º degrees. In drilling soft materials, the angle may be increased under heavy feeds. For hard materials, the recommended angle is 9º degrees. If reduced further the drill cannot cut into the metal and may break in the centre along the web.

Rake angle: It is the angle between the flute and the workpiece that is usually 70-75º degrees. This helps to secure the lip over the correct space to curl the chips. If more there will be no edge for cutting and if less the cutting edge will be too thin and may break under strain.

5. Cutting conditions in drilling

• The twist drill is a cutting tool with two symmetrical opposite cutting edges, each removing part of the material in the form of chip.

• Fig. : Basics of a drilling operation.

6. Motions of Drill and Cutting Velocity

• In drilling, the primary motion is the rotation of the cutting tool held in the spindle.

• Drills execute also the secondary feed motion.• Cutting velocity V in drilling is not a constant

along the major cutting edge as opposed to the other machining operations.

It is zero at the center of the twist drill, and has a maximum value at the drill corner.

The maximum cutting speed is given by:

V = πDNwhere D is the drill diameter, and N is the rotational speed of the drill.

• As in the case of turning and milling, cutting speed V is first calculated or selected from appropriate reference sources, and then the rotational speed of the drill N, which is used to adjust drill press controls, is calculated.

7. Feed in Drilling• Feed (f) is the distance that the drill penetrates

per revolution (mm/rev), the share of each cutting edge is = f/2

• Two types of feed in drilling can be identified: feed per tooth fz: has the same meaning as in the

other multi-tooth cutting tools.Feeds per tooth are roughly proportional to drill diameter, higher feeds for larger diameter drills.

• feed per minute fm: feed per minute is calculated taking into account the rotational speed N,

fm = 2fzN

• Feed per minute is used to adjust the feed change gears.

• Depth of cut d is equal to the half of drill diameter, d = 1⁄2 D

where D is the drill diameter. • In core drilling, a drilling operation used to enlarge an

existing hole of diameter D(hole), depth of cut is given by

d = 1⁄2 (D(drill) – D(hole)) where D(drill) is the drill diameter, and D(hole) is the

diameter of the hole being enlarged.

8. Drilling time

• Drilling time (T) can be given by the equation; T = L / f N;

Where f is the feed (mm/rev) N is the rotational speed (rpm) L is the sum of hole depth, approach and over travel distances.*The approach is usually considered as 0.4D while over travel ranges from 1 to 3mm.

9. Drilling operations

• Drilling is used to drill a round blind or through hole in a solid material. If the hole is larger than ~30 mm, its a good idea to drill a smaller pilot hole before core drilling the final one. For holes larger than ~50 mm, three-step drilling is recomended;

• Core drilling is used to increase the diameter of an existing hole.

• Step drilling is used to drill a stepped (multi-diameter) hole in a solid material.

• Counterboring provides a stepped hole again but with flat and perpendicular relative to hole axis face. The hole is used to seat internal hexagonal bolt heads.

• Countersinking is similar to counterboring, except that the step is conical for flat head screws.

• Reaming provides a better tolerance and surface finish to an initially drilled hole. Reaming slightly increases the hole diameter. The tool is called reamer;

• Center drilling is used to drill a starting hole to precisely define the location for subsequent drilling. The tool is called center drill. A center drill has a thick shaft and very short flutes. It is therefore very stiff and will not walk as the hole is getting started.

• Gun drilling is a specific operation to drill holes with very large length-to-diameter ratio up to L/D ~300. There are several modifications of this operation but in all cases cutting fluid is delivered directly to the cutting zone internally through the drill to cool and lubricate the cutting edges, and to remove the chips

10. Reamers

• The reamer used in reaming operation has similar geometry as for twist drill .

• The difference in geometry between a reamer and a twist drill are:

The reamer contains four to eight straight or helical flutes, respectively cutting edges.

The tip is very short and does not contain any cutting edges.

11. Drill materials

• Drills are normally made of high-speed steel (HSS) but carbide-tipped drills, and drills with mechanically attached carbide inserts are commonly used in many operations, especially on CNC drilling machines

12. Apparatus needed during drilling operation

• Normally, holes produced by drilling are bigger than the drill diameter and depending on its applications; the drilled holes will subjected to other operations such as reaming or honing to better surface finish and dimensional accuracy

• There are also several apparatus needed during the drilling operation as shown below:

Drilling machine Center punch Hammer Center drill Twist drills Coolant Vernier caliper Two flute drill set: i. Center drill; ii. Countersink drill; iii. Counter bore drill;

iv. Drill various diameter

Part II. Welding Processes

Welding Processes

Ship Structures

1. INTRODUCTION

• Welding is the process of permanently joining two or more metal parts, by melting both materials. The molten materials quickly cool, and the two metals are permanently bonded.

• Modern welding technology started just before the end of the 19th century with the development of methods for generating high temperature in localized zones.

• Welding generally requires a heat source to produce a high temperature zone to melt the material, though it is possible to weld two metal pieces without much increase in temperature.

• Welding process can be done with or without the application of pressure, and with or without the use of filler metal.

2. Classification of Welding

• Fusion Welding or Non-Pressure Welding The materials at the joint are heated to a molten

state and allowed to solidify.(Ex) Gas welding, Electric Arc welding

• Pressure Welding or Plastic Welding The piece of metal to be joined are heated to a

plastic state and forced together by external pressure.(Ex) Resistance welding

Classification of Welding (Cont’)

Fusion Welding Pressure Welding

Homogeneous Heterogeneous

Brazing SolderingGas Welding

Electroslag

High Energy Beam

Electric Arc

MIGTIG

Shielded Metal Arc – “Stick”

Friction Welding

2.1. Fusion Welding Principles

• Base metal is melted• Filler metal may be added• Heat is supplied by various means

– Oxyacetylene gas– Electric Arc– Plasma Arc– Laser

Fusion Weld Zone

Fig : Characteristics of a typical fusion weld zone in oxyfuel gas and arc welding.

Fusion Welding

BASE METAL

WELD

SOLIDIFIED SLAG

ARC POOL

WELDING ATMOSPHERE

CORE WIRE

ELECTRODE COATING

ARC STREAM

PENETRATION DEPTH

Weld Metal Protection

• During fusion welding, the molten metal in the weld “puddle” is susceptible to oxidation

• Must protect weld puddle (arc pool) from the atmosphere

• Methods– Weld Fluxes– Inert Gases– Vacuum

Weld Fluxes

• Typical fluxes– SiO2, TiO2, FeO, MgO, Al2O3

• Produces a gaseous shield to prevent contamination the oxygen and nitrogen of the air.

• Act as scavengers to reduce oxides.• Add alloying elements to the weld.• Influence shape of weld bead during

solidification.

Inert Gases

• Argon, helium, nitrogen, and carbon dioxide• Form a protective envelope around the weld

area• Used in

– MIG– TIG– Shield Metal Arc

Vacuum

• Produce high-quality welds• Used in electron beam welding• Nuclear/special metal applications

– Zr, Hf, Ti• Reduces impurities by a factor of 20 versus

other methods• Expensive and time-consuming

3. Types of Fusion Welding

• Oxyacetylene Cutting/Welding• Shielded Metal Arc (“Stick”)• Metal Inert Gas (MIG) • Tungsten Inert Gas (TIG)

3.1. Oxy-acetylene Arc Welding

• Flame formed by burning a mix of acetylene (C2H2) and oxygen

• Fusion of metal is achieved by passing the inner cone of the flame over the metal

• Oxyacetylene can also be used for cutting metals

Inner Cone: 5000-6300 deg F Combustion Envelope 3800 deg F

2300 deg FTORCH TIP

Oxyacetylene flames

Fig : Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame. The gas mixture in (a) is basically equal volumes of oxygen and acetylene.

Oxyacetylene flames• Oxygen is turned on, flame immediately changes into a long white inner area

(Feather) surrounded by a transparent blue envelope is called Carburizing flame (30000C)

• Addition of little more oxygen give a bright whitish cone surrounded by the transparent blue envelope is called Neutral flame (It has a balance of fuel gas and oxygen) (32000c)

Used for welding steels, aluminium, copper and cast iron• If more oxygen is added, the cone becomes darker and more pointed, while the

envelope becomes shorter and more fierce is called Oxidizing flame Has the highest temperature about 34000C Used for welding brass and brazing operation

Oxyacetylene Torch

Fig. (a) General view of and (b) cross-section of a torch used in oxyacetylene welding. The acetylene valve is opened first; the gas is lit with a spark lighter or a pilot light; then the oxygen valve is opened and the flame adjusted. (c) Basic equipment used in oxyfuel-gas welding. To ensure correct connections, all threads on acetylene fittings are left-handed, whereas those for oxygen are right-handed. Oxygen regulators are usually painted green, and acetylene regulators red.

3.2. Shielded Metal Arc (Stick)• An electric arc is generated between a coated

electrode and the parent metal• The coated electrode carries the electric current to

form the arc, produces a gas to control the atmosphere and provides filler metal for the weld bead

• Electric current may be AC or DC. If the current is DC, the polarity will affect the weld size and application

Shielded Metal Arc (Stick)

Fig. Schematic illustration of the shielded metal-arc welding process. About 50% of all large-scale industrial welding operations use this process.

Shielded Metal Arc (con’t)• Process:

– Intense heat at the arc melts the tip of the electrode– Tiny drops of metal enter the arc stream and are

deposited on the parent metal– As molten metal is deposited, a slag forms over the bead

which serves as an insulation against air contaminants during cooling

– After a weld ‘pass’ is allowed the cool, the oxide layer is removed by a chipping hammer and then cleaned with a wirebrush before the next pass.

3.3. Inert Gas Welding

• For materials such as Al and its alloys or Ti which quickly form oxide layers. The shielded gases used are:

Argon, Helium, nitrogen, carbon dioxide or mixture of them.

Argon and Helium are completely inert and therefore they provide a complete inert atmosphere around the puddle.

• Uses a consumable electrode (filler wire made of the base metal) and is fed automatically from a coil into the arc.

• Inert gas is typically Argon

Metal Inert Gas (MIG)

BASE METAL PUDDLE

POWER SOURCE

DRIVE WHEELSCONSUMABLE ELECTRODE

ARC COLUMNSHIELDING GAS

• Tungsten electrode acts as a cathode• A plasma is produced between the tungsten cathode and the base

metal which heats the base metal to its melting point• Filler metal can be added to the weld pool

Tungsten Inert Gas (TIG)

BASE METAL PUDDLE

POWER SOURCE

ARC COLUMNSHIELDING GAS

TUNGSTEN ELECTRODE

+ +

BASE METAL (ANODE)

TUNGSTEN ELECTRODE

(CATHODE)

- - -+ +

4. Submerged arc welding

Fig : Schematic illustration of the submerged-arc welding process and equipment. The unfused flux is recovered and reused .

Submerged arc welding (Cont)

Fig : Simplified schematic illustration of the submerged-arc welding process

Submerged arc welding (Cont)• Submerged arc welding (SAW) is an electric arc welding

process that uses a continuous, consumable bare wire electrode.

• The arc shielding is provided by a cover of granular flux.• The electrode wire is fed automatically from a coil into the

arc.• The flux is introduced into the joint slightly ahead of the weld

arc by gravity from a hopper.

5. Flux cored Arc Welding

• Flux cored arc welding (FCAW) is similar to a gas metal arc welding (MIG).

• Electrode is tubular in shape and is filled with flux.

• Cored electrodes produce more stable arc, improve weld contour and produce better mechanical properties.

• Flux is more flexible than others.

Equipment used in MIG and FCAW Welding Operations

Fig : Basic equipment used in gas metal-arc (MIG) and (FCAW) welding operations

6. Plasma-Arc Welding Process

• Plasma Arc Welding (PAW) is a special form of gas tungsten arc welding in which a plasma arc is directed at the weld area.

• The tungsten electrode is contained in a specially designed nozzle that focuses a high-velocity stream of inert gas (for example, argon or argon-hydrogen mixtures, and helium) into the region of the arc to produce a high-velocity plasma jet of small diameter and very high-energy density.

• Temperatures in plasma arc welding reach 30,000o C or greater, hot enough to melt any known metal.

Plasma-Arc Welding Process (Cont)

Fig.: Two types of plasma-arc welding processes: (a) transferred, (b) nontransferred. Deep and narrow welds can be made by this process at high welding speeds.

7.Welding Positions

8.Main Joint Design

BUTT JOINTBUTT JOINT

STRAP JOINT

LAP JOINT

FILLET JOINT

CORNER JOINT

Derived Welding Joint Design

Fig. Examples of welded joints and their terminology.

9. Resistance welding

• Resistance welding (RW) is a group of fusion welding processes that utilizes a combination of heat and pressure to accomplish coalescence.

• The heat required is generated by electrical resistance to current flow at the interface of two parts to be welded.

• The resistance welding processes of most commercial importance are spot and seam welding.

9.1. Resistance Spot Welding• Resistance spot welding (RSW) is a resistance

welding process in which fusion of the base metal is achieved at one location by opposing electrodes.

• Resistance spot welding is widely used in mass production of automobiles, appliances, metal furniture, and other products made of sheet metal of thickness 3 mm or less.

• The cycle in a spot welding operation consists of the steps depicted in the figure:

Steps in a spot welding cycle: (1) parts inserted between open electrodes, (2) electrodes close and force is applied, (3) weld time (current is switched), (4) current is turned off but force is maintained, and (5) electrodes are opened, and the welded assembly is removed.

9.2. Resistance Seam Welding

• In Resistance Seam Welding (RSEW), the electrodes are two rotating wheels as shown in the figure:

Different types of seam welding

Different types of seam welding, (from left to right) conventional seam welding, roll spot welding, continuous resistance seam welding.

Different types of seam welding (Cont’)

• The spacing between the weld nuggets in resistance seam welding depends on the motion of the electrode wheels relative to the application of the weld current.

• In the usual method of operation, called continuous motion welding, the wheel is rotated continuously at a constant velocity, and current is turned on at timing intervals consistent with the desired spacing between spot welds along the seam so that overlapping weld spots are produced.

Different types of seam welding (Cont’)

• But if the frequency of current switching is reduced sufficiently, there will be spacing between the weld spots, and this method is termed roll spot welding.

• In another variation, the welding current remains on at a constant level so that a truly continuous welding seam is produced.

10. Generalized Welding Symbol

FAR SIDE DETAILS

ARROW SIDE DETAILS

Field weld symbol

Weld all-around for pipes, etc.

L1-L2

L1-L2

D = Weld Depth (usually equal to plate thickness)

L1 = Weld Length

L2 = Distance between centers for stitched welds

The Field Weld Symbol (generally used in arc welding)is a guide for installation. Shipyards normally do not use it, except in modular construction.

ElectrodeMaterial

D

D

Weld Geometry

Example Welding Symbol

1/2” 1/2”

1/2

1/2

One-sided welds are max 80% efficientTwo sided are 100% efficient

Geometry symbol for V-groove

Weld Symbols (Butt Joints)

Backing

Weld Symbol (Fillet Joints)

Weld Symbol (Corner Joints)

General Design Guidelines

11. Electrode Designations

Weld Quality and Testing in Arc Welding

1. WELD QUALITY

• Welding discontinuities can be caused by inadequate or careless application.

• The major discontinuities that affect weld quality are: Porosity Slag Inclusions Incomplete fusion and penetration Weld profile Lamellar tears Cracks Surface damage Residual stresses

Discontinuities and Defects in Fusion Welds

Fig.1. Examples of various discontinuities in fusion welds.

Fig.2. Schematic illustration of various defects in fusion welds.

1.1. Porosity• Caused by gases released during melting of the weld area but

trapped during solidification, chemical reactions, Contaminants

• They are in form of spheres or elongated pockets.• Porosity can be reduced by Proper selection of electrodes Improved welding techniques Proper cleaning and prevention of contaminants Reduced welding speeds

1.2. Slag Inclusions

• Compounds such as oxides ,fluxes, and electrode-coating materials that are trapped in the weld Zone.

• Prevention can be done by following practices : Cleaning the weld bed surface before the next layer

is deposited. Providing enough shielding gas. Redesigning the joint.

1.3. Incomplete Fusion and Penetration

• Produces lack of weld beads• Practices for better weld : Raising the temperature of the base metal. Cleaning the weld area, prior to the welding. Changing the joint design and type of electrode. Providing enough shielding gas.

1.4. Penetration

• Incomplete penetration occurs when the depth of the welded joint is insufficient.

• Penetration can be improved by the following practices :

Increasing the heat Input. Reducing the travel speed during the welding. Changing the joint design. Ensuring the surfaces to be joined fit properly.

1.5. Weld Profile

• Under filling results when the joint is not filed with the proper amount of weld metal.

• Undercutting results from the melting away of the base metal and consequent generation of a groove in the shape of a sharp recess or notch.

• Overlap is a surface discontinuity usually caused by poor welding practice and by the selection of improper material.

1.6. Cracks

• Cracks occur in various directions and various locations

• Factors causing cracks:

Temperature gradients that cause thermal stresses in the weld zone.

Variations in the composition of the weld zone. Embrittlement of grain boundaries Inability of the weld metal to contract during

cooling.

Types of cracks

Fig : Types of cracks (in welded joints) caused by thermal stresses that develop during solidification and contraction of the weld bead and the surrounding structure. (a) Crater cracks (b) Various types of cracks in butt and T joints.

1.7. Lamellar tears• Occurred due to the shrinkage of the restrained

components in the structure during cooling.• Can be avoided by providing for shrinkage of the

members.• Changing the joint design. • Surface Damage : These discontinuities may

adversely affect the properties of welded structure, particularly for notch sensitive metals.

1.8. Residual Stresses

• Caused because of localized heating and cooling during welding, expansion and contraction of the weld area causes residual stresses in the work piece.

• Distortion, Warping and buckling of welded parts• Stress corrosion cracking• Further distortion if a portion of the welded

structure is subsequently removed• Reduced fatigue life

1.9. Distortion of Parts After Welding

Fig. Distortion of parts after welding. (a) Butt joints and (b) fillet welds. Distortion is caused by differential thermal expansion and contraction of different regions of the welded assembly.

2. Weld Testing2.1. Destructive Techniques

Fig. Destructive Techniques: (a) Specimen for longitudinal tension-shear testing; (b) specimen for transfer tension-shear testing; (c) wraparound bend test method; (d) three-point bending of welded specimens.

2.2. Non-Destructive testing

• Often weld structures need to be tested Non-Destructively

• Non-Destructive testing are : Visual Liquid-penetrant Radiographic Magnetic-particle Ultrasonic

Part 3: Turning operations

1. Introduction• Turning is a machining process to produce parts

round in shape by a single point tool on lathe Machines.

• The cutting tool is fed either linearly in the direction parallel or perpendicular to the axis of rotation of the workpiece, or along a specified path to produce complex rotational shapes.

• The primary motion of cutting in turning is the rotation of the workpiece, and the secondary motion of cutting is the feed motion of the cutting tool (See figure on the next slide).

2. Principal Surfaces and Motions

3. Cutting conditions in turning

• Cutting speed in turning V in m/s is related to the rotational speed of the workpiece by the equation:

V = πDN (m/sec)where D is the diameter of the workpiece, m; N is the rotational speed of the workpiece, rev/s (rpm).

• Feed in turning is generally expressed in mm tr-1 (millimetres per revolution).

• The turning operation reduces the diameter of the workpiece from the initial diameter Do to the final diameter Df. The change in diameter is actually two times depth of cut, d:

2d = Do - Df• The volumetric rate of material removal (so-

called material removal rate, mrr) is defined bymrr = Vfd

• When using this equation, care must be exercised to assure that the units for V are consistent with those for f and d.

4. Operations in turning

• Turning of cylindrical surfaces• Turning of flat surfaces• Threading• Form turning• Knurling• Drilling, Internal grooving and Boring

4.1. Turning of cylindrical surfaces

The lathe can be used to reduce the diameter of a part to a desired dimension. The resulting machined surface is cylindrical.

4.2. Turning of flat surfaces

A lathe can be used to create a smooth, flat face very accurately perpendicular to the axis of a cylindrical part.

Tool is fed radially or axially to create a flat machined surface.

4.3. Threading Threading is turning operation on lathe machine to

cut an helical groove on or in the workpiece, which is actually a thread, by The single-point cutting tool at a feed exactly equal to the thread pitch.

The procedure calls for correct settings of the machine, and also that the helix be restarted at the same location each time if multiple passes are required to cut the entire depth of thread.

The tool point must be ground so that it has the same profile as the thread to be cut.

Another possibility is to cut threads by means of a thread die (external threads), or a tap (internal threads). These operations are generally performed manually for small thread diameters.

4.4. Form turning

Cutting tool has a shape that is imparted to the workpiece by plunging the tool into the workpiece.

In form turning, cutting tool is complex and expensive but feed is linear and does not require special machine tools or devices.

4.5. Contour turning (profiling)

Cutting tool has a simple shape, but the feed motion is complex; cutting tool is fed along a contour thus creating a contoured shape on the workpiece.

For profiling, special lathes* or devices are required.

Producing tapers on a lathe is a specific task and contour turning is just one of the possible solutions**.

4.6. Drilling, Internal grooving and Boring

4.7. Knurling

This is not a machining operation at all, because it does not involve material removal. Instead, it is a metal forming operation used to produce a regular crosshatched pattern in the work surface.

5. Lathes

• A lathe is a machine tool that rotates the workpiece against a tool whose position it controls.

• The spindle (see picture in the next page) is the part of the lathe that rotates. Various work holding attachments such as three jaw chucks, collets, and centers can be held in the spindle. The spindle is driven by an electric motor through a system of belt drives and gear trains.

• Spindle rotational speed is controlled by varying the geometry of the drive train.

6. Principal components of a lathe

• The tailstock can be used to support the end of the workpiece with a center, or to hold tools for drilling, reaming, threading, or cutting tapers.

• The carriage controls and supports the cutting tool. It consists of:

a saddle that slides along the ways;an apron that controls the feed mechanisms;a cross slide that controls transverse motion of the tool;a tool post that holds the cutting tools.

7. Work holding methods in lathes

8. Turning tapers on lathes

• A taper is a conical shape.

• The tailstock offset h is defined by h = Lsinα

where L is the length of workpiece, and α is the half of the taper angle.

9. Cutting tools

Left and Right-hand turning tool bit

Shapes of Tool Bits

END OF PART 3

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