Engineering Drawing General

1.1 Introduction to Engineering Drawing1.1.1 Introduction1.1.2 Sheet Sizes1.1.3 Layout and Drawing Sheets1.1.4 Drawing Zones1.1.5 Drawing Scales1.1.6 Line Types or Styles1.1.7 Lettering

1.2Methods of Projection 1.2.1 Introduction1.2.2 Orthographic Projection1.2.3 Isometric Projection1.2.4 Oblique Projection1.2.5 Auxiliary Projection

1.3 Sections1.4 Dimensioning and Tolerancing1.5 Conventional Representations1.6 Surface Roughness1.7 Fasteners1.8 Drawing Tips1.9 Missing Views

1. Engineering Drawing

1.1.1 Introduction

Why Engineering Drawings ?• Drawing is the universal language of engineering• Engineering drawing is a formal and precise way of communicating information about the Shape,

Size, Features and Precision of physical objects• Engineering drawings communicate product design and manufacturing information in a reliable

and unambiguous manner regardless of languageDrawing Standards• Engineering drawings and other technical drawings have to be done in ways that all engineers

can recognize. • These ways are called drawing standards or conventions

Drawings are made to standard so that they : Use same symbols, lines, dimension techniques etc., can be understood internationally

Some of the international standards are :• ANSI - American National Standards Institute• ISO - International Standards Organization• DIN - Deutsches Institut fur Normung• BSI - British Standards Institute• JIS - Japanese Industry Standard

1.1 Introduction to Engineering Drawing

1.1.2 Drawing Sheet SizesThe following table defines the ISO ‘A’ series standard drawing sizes, and their letter designations

Multi-sheet drawings• Multi-sheet drawings are permitted in all sheet sizes• The first sheet of a multi-sheet drawing shall always contain the complete Title block, List of

Material, Revision Block, and general notes• All sheets of multi-sheet drawings shall be of the same letter size. Use of multi-sheet drawings

shall be found to be advantageous for certain types of schematics and diagrams• Sheet numbering for all first sheets shall include the total number of sheets, as “SHEET 1 OF 1,”

“SHEET 1 OF 2,” etc.

Designation

Dimensions

A0 841 mm x 1189 mmA1 594 mm x 841 mmA2 420 mm x 594 mmA3 297 mm x 420 mmA4 210 mm x 297 mmA5 149 mm x 210 mm


1.1.3 Drawing Sheet Layout• Paper space is a sheet layout environment where you can specify the size of your sheet, add a title block,

display multiple views of your model, and create dimensions and notes for your drawing

This is the layout of a typical sheet, showing the drawing layout, a typical title block, BOM (parts list) and revision table

Revision Block

BOM (Parts list)

Title Block

Drawing Layout


Sheet Frame/Border• It is standard practice for a drawing frame to be printed on each sheet, defining a margin around the

outside of drawing area.• Drawing frames are standardized for each size of paper

Drawing Frame

Drawing Layout


Title BlockThe title block is normally placed in the bottom right of the drawing frame, and it should contain the

following information: 1. Name of the company or organization 2. Title of the drawing - Description of the part or assembly3. Drawing number - Which is generally a unique filing identifier of part or assembly for archiving or

cross referencing4. The scale – Identifies the main scale that the drawings is drawn e.g., 1:1 or 1:2 5. Sheet Size – Size of the drawing sheet used for the drawing6. Projection system symbol - Either first or third angle projection, generally shown symbolically7. Drawn by - the signature or initials of the draftsman, checker, approving officer, and issuing officer,

with the respective dates8. Date - The date the drawing was created or amended on9. Material - What the item is made of, e.g. Mild steel, Aluminum, if critical include particular grade10. Surface Finish - The general component surface roughness tolerance11. Sheet Number – Sheet number is indicated on the drawing including total number of sheets used

for the drawing12. other information as required


Example : Title Block for Part Drawing

Revision Block• A revision table is normally located in the upper right of the drawing frame, or at the bottom on the left side

of the title block. • All modifications to the drawing should be documented here• The revision table contains a row for every stage of revisions made to the drawing• This row contains :

• Zone• Revision Letter• Date of revision• Brief description of changes made• Signature/initials of the reviser

The revision table expands by one row each time the drawing changes, often requiring that its size be restricted to the most previous revisions in order to leave space for the actual drawing!


ZONE

REVISION REF DATE DESCRIPTION SIG

A3 A 01/02/09 XXXXXXXXXXXXXX XX

B5 B 15/06/09 XXXXXXXXXXXXXX XX

C7 C 05/01/10 XXXXXXXXXXXXXX XX

BOM (Bill of Material or Parts List)If the drawing contains a number of parts, or if it is an assembly drawing, a tabulated parts list is attached to

the bottom right of the drawing frame, just above the title blockThe Parts List should give the following information :

• Part Number• Part Name/Description• Drawing Number of each individual part• Material Specifications• Quantity required• Other applicable information

The revision table expands by one row each time the drawing changes, often requiring that its size be restricted to the most previous revisions in order to leave space for the actual drawing!


1.1.4 Zones• A drawing may be divided up into a grid using letters and numbers• Zoning allows easy references to various parts of the drawing by referring a zone – for example A1• When zoning is used it is located inside the drawing frame

Zone – A1

Horizontal Zone identificationNumbered from Left-hand edge

Verti

cal Z

one

iden

tifica

tion

Alph

abet

ically

le

ttere

d fro

m T

op

edge


1.1.5 Scales• All engineering drawings can be classified as either drawings with scale or those not drawn to scale• Drawings without scale are intended to present only functional information about the component and the

system• Scaled drawing used to obtain information such as physical dimensions, tolerances and materials that

allows the fabrication or construction of the component or system• Components or systems can be drawn to full scale in a more convenient and easy to read the different

parameters. Also a small component can be scaled up or enlarged , so that its details can be seen clearly when drawn on paper

Preferred Scales for Engineering Drawings

• Decimal multiples of these base scales are also used e.g., 1:20, 1:50, 20:1, 50:1• The scale should normally be noted in the title block of a drawing• When more than one scale is used they should be shown close to the views to which they refer


Actual/Full Size 1:1Reduction 1:2; 1:5; 1:10

Enlargement 2:1; 5:1; 10:1

Line Type/Style Example Application

Center Line

• Center lines shall be composed of long and short dashes, alternately and evenly spaced, with a long dash at each end• Center lines drawn through the center of a feature and is used to indicate the travel of a center

Dimension Line

• Dimension lines shall terminate in arrowheads at each end• They shall be unbroken except where space is required for the dimension

Leader Line• Leader shall be used to indicate a part or portion to which a number, note, or other reference applies

Phantom Line

• Phantom lines shall be used to indicate the alternate position of parts of the item delineated, repeated detail, or the relative position of an absent part• Composed of alternating one long and two short dashes, evenly spaced, with a long dash at each end

1.1.6 Line Styles or Types• When a designer works with an engineering drawing they must be familiar with the precise meaning of

the various line styles, abbreviations, drawing simplifications and terminology as specified in the relevant standards

• Each line on a drawing represents specific precise information regarding the components design



Hidden Lines•Hidden lines shall consist of short dashes, evenly spaced• These lines are used to show the hidden features of a part

Break Line (Short or Long)

• Short breaks shall be indicated by solid freehand lines.• For long breaks, full ruled lines with freehand zigzags shall be used.• Shafts rods, tubes, etc., which have a portion of their length broken out, shall have the ends of the break drawn as indicated in fig.

Datum Line• Datum lines shall be used to indicate the position of a datum plane• It consist of one long dash and two short dashes

Visible Lines or Outlines

• The outline or visible line shall be used for all lines on the drawing representing visible lines on the object



Cutting –Plane/Viewing Planes Lines

• The cutting-plane lines shall be used to indicate a plane or planes in which a section is taken• The viewing-plane lines shall be used to indicate the plane or planes from which a surface or surfaces are viewed

Cutting-Plane for Complex or Off-set Planes

• On complex views, or when the cutting planes are bent or offset, the cutting planes shall be indicated as shown in Fig.


Example for Line Conventions


1.1.7 LetteringAll characters on drawing must be legible and consistentNo particular style is required, but characters should be consistent on the same drawingCapital letters are preferred to lower case ones

Preferred Size of lettering is given as a minimum height, relating to drawing size as shown below

Application Drawing Sheet Size Min. Character Height

Drawing Titles and Numbers, etc.

A0, A1, A2 & A3 7 mmA4 5 mm

Dimensions and NotesA0 3.5 mm

A1, A2, A3 & A4 2.5 mm


1.2.1 Introduction• In order to interpret and communicate the graphical description of the solid objects with engineering

drawings a designer must have a sound understanding of it's use and a clear vision of how the various projections are created

• A view of an object is known technically as a projection• A projection is a view conceived to be drawn or projected on to a plane, known as the plane of projection• The purpose of a drawing is to show the size and shape of the object. A drawing can also provide certain

information on how an object is to be made. Various methods of presentation are available to the designer or drafter. However, the best way to show every feature of an object in its true size and shape is to use an arrangement of more than one view known as a multiview drawing.

• Multiple views are created using the principles of orthographic projection

Multiple views and projections

1.2 Methods of Projection

1.2.2 Orthographic projection• orthographic projection is a system of views of an object formed by projectors from the object

perpendicular to the desired plane of projection

• Orthographic projections on mutually perpendicular projection planes will fully describe the object in its shape and size. Hence, all design and manufacturing drawings are made with orthographic projectionsSix Basic Views

• You can project in six orthogonal directions. The resulting views are called basic views.• You may imagine that the 3D object is placed inside a transparent box, and views are projected

orthogonally onto the six walls of the box. By unfolding the box, six views of the object are possible


Quadrants in descriptive geometry•Modern orthographic projection is derived from Gaspard Monge’s descriptive geometry•Monge defined a reference system of two viewing planes, horizontal H ("ground") and vertical V ("backdrop"). •These two planes intersect to partition 3D space into 4 quadrants


I QuadrantAbove HPIn front of VP

II QuadrantAbove HPBehind VP

IV QuadrantBehind HPIn front of VP

III QuadrantBelow HPBehind VP

Reference Line

Types of Orthographic Projections•There are two predominant orthographic projections used today - First Angle and Third Angle Projections

First-Angle Projection

Third-Angle Projection


First-Angle Projection• First Angle Projection is used in Europe and Asia• In First Angle Projection we place our object in the First Quadrant. • This means that the Vertical Plane is behind the object and the Horizontal Plane is underneath the object

In First angle projection: • The view from the front is in the middle • The view from the left is on the right • The view from the right is on the left • The view from the top is on the bottom • The view from the bottom is on the top • The view from the rear is on the far right


Third-Angle Projection• Third angle Projection is used in America and Australia• In Third Angle Projection the Object is placed in the Third Quadrant. • This means that the Vertical Plane is in front of the object and the Horizontal Plane is above the object

In Third angle projection :

• A view from the left of the front view is drawn on the left.

• A view from the right is drawn on the right. • A view from the top of the front view is drawn

on the top. • A view from the bottom is drawn on the bottom.


• Because the difference between projection methods is so small this presents little or no difficulty for engineers to interpret drawings, provided we indicate on the drawing which system we are using

• The symbols for First Angle and Third Angle projection are shown below. • Both systems of projection, First and Third angle, are approved internationally and have equal status• The symbols are derived from a cut cone which has been projected in First or Third Angle respectively

The recommended proportions for the projection symbols are shown in above fig.


Orthographic projection is used as an unambiguous and accurate way of providing information, primarily for manufacturing and detail design. This form of representation can however make it difficult to visualise objects. • Pictorial views can be created to give a more three dimensional impression of the object. • There are three types of pictorial projections commonly used :

• Isometric• Oblique• Perspective


1.2.3 Isometric projection• Isometric projection is a method for visually representing three-dimensional objects in two dimensions in technical and engineering drawings• An isometric view of an object can be obtained by choosing the viewing direction in a way that the angles between the projection of the x, y, and z axes are all the same, or 120°• For example when taking a cube, this is done by first looking straight towards one face. Next cube is rotated ± 45° about the vertical axis, followed by rotation of 30° about the horizontal axis

1.2.4 Oblique projection• An oblique projection is a simple type of graphical projection used for producing pictorial, two-dimensional images of three-dimensional objects• One way to draw using an oblique view is to draw the side of the object you are looking at in two dimensions, i.e. flat, and then draw the other sides at an angle of 30 or 45 degrees, but instead of drawing the sides full size they are only drawn with half the depth creating 'forced depth' - adding an element of realism to the object• Oblique drawings look very unconvincing to the eye. For this reason oblique is rarely used by professional designer and engineers


1.2.5 Perspective projection• Perspective is an approximate representation on a flat surface, of an image as it is perceived by the eye. • The two most characteristic features of perspective are that objects are drawn:

• Smaller as their distance from the observer increases• Foreshortened: the size of an object's dimensions along the line of sight are relatively shorter than dimensions across the line of sight

Parallel lines appear to converge and meet at what is referred to as the vanishing point. You can have one, two or three vanishing points (VP)

Two-point perspective drawingOne-point perspective drawing


1.2. 6 Auxiliary projection• An auxiliary view is an orthographic view that is projected into any plane other than one of the six principal views• These views are typically used when an object contains some sort of inclined plane• Using the auxiliary view allows for that inclined plane (and any other significant features) to be projected in their true size and shape• The true size and shape of any feature in an engineering drawing can only be known when the Line of Sight (LOS) is perpendicular to the plane being referenced

Auxiliary projection principle Auxiliary and side views

compared

Auxiliary view arrangement


1.3 SectionsProjecting views in a drawing will allow us to see the external features of an object. But most of the times it is necessary to view the internal features of the object also, this is accomplished by slicing through the object and producing a sectional or section viewSectional or Section views are produced to:

• clarify details• show internal features clearly• aid dimensioning• show cross-section shape• clarify an assembly

Sectioning• To show the inside details of a component it is imagined to be cut or sectioned along a plane, called cutting plane. • The location of a section is indicated by a cutting plane with reference letters and arrowheads showing the direction in which the section is viewed

Section in one plane

Views should not be rotated; however, if views have to be rotated for a legitimate reason, the angle and direction of rotation must be given

1.3 SectionsCommonly used sectioning types in

drawing

Section in 2 parallel plane

Symmetrical parts can be shown in half sections

part or ‘broken-out’ section

Sectioning Objects with Holes, Ribs, Etc

Revolved sections are useful when clarifying local cross-section shapes as shown in Fig.

There are some exceptions to the general rules of sectioning ; Webs, Shafts, Rods, and Spindles, These parts would not be shown as sections, if their center lines lie on the cutting plane

Web Sections

Shafts, Rods, Spindle Sections

1.3 Sections

Hatching• Surfaces cut by the cutting plane are usually hatched to show areas of sections. • It is executed by thin lines at an angle of 450 to the axis or to the main outline of the section• The hatching of adjacent components shall be carried out with different directions or spacing

In case of more than 2 adjacent components, hatching is done in such a way to make sections evident, in different directions and by varying the pitch or spacing of the hatching lines

Spacing between the hatching lines should be chosen in proportion to the area of the section to be hatched

1.3 Sections

Detail Views :• When there is a great disparity between feature size, or views are overcrowded with dimensions, a detail view can be used to capture the feature(s) of interest and display them in a view of greater scale• This detail is a partial view which shows a portion of another view in the same plane and will usually depict greater detail. • Details should not be rotated

1.3 Sections

Identification of Sections, Views, and Details•Identifying letters for sections, views, and details are assigned in alphabetical sequence as follows:

• For sections and such views as “A-A”, use hyphenated letters.• After “Z-Z,” begin: “AA-AA,” “AB-AB,” etc

• For encircled details such as detail “A”, use single letters. • After “Z,” begin: “AA,” “AB,” etc

• The letters “I,” “O,” and “Q,” either as a single letter or as double-letter entries, shall not be used• A designated letter or combination of letters on a released drawing shall not be used for another section, view, or detail on the same drawing

1.3 Sections

DIMENSIONS!!!: These are the most important and most complicated part of the drawing. There is more to it than just the numerical values!The purpose of dimensioning is to provide a clear and complete description of an object. A complete set of dimensions will permit only one interpretation needed to construct the part. Dimensioning should follow these guidelines :

• Standards and conventions should be followed• Correct values must be given. • Dimensions must be placed in appropriate positions. • All required dimensions and tolerances, etc, should be expressed directly on the drawing, and

nothing duplicated. • Appropriate line quality must be used for legibility.• The drawing must include the minimum number of dimensions required to accurately

manufacture the design• It should not be necessary for the operator manufacturing the component to have to calculate

any dimensions

1.4 Dimensioning and Tolerancing

Basic DefinitionsDimension line is a thin line, with arrowheads at each end. An arrowhead is approximately 3 mm long and 1 mm wide. That is, the length is roughly three times the width

Extension line extends a line on the object to the dimension line. Extension lines begin 1.5 mm from the object and extend 3 mm from the last dimension lineLeader is a thin line used to connect a dimension with a particular area. A leader may also be used to indicate a note or comment about a specific area

Edges A and B are being used as the reference edges


Types of dimensioning• Parallel Dimensioning : Parallel dimensioning consists of several dimensions originating from one projection line

• Superimposed Running Dimensions :Superimposed running dimensioning simplifies parallel dimensions in order to reduce the space used on a drawing. The common origin for the dimension lines is indicated by a small circle at the intersection of the first dimension and the projection line


• Chain Dimensioning : Chains of dimension should only be used if the function of the object won't be affected by the accumulation of the tolerances

• Combined Dimensioning :A combined dimension uses both chain and parallel dimensioning


Radii

Circles on engineering drawings are usually either spheres, holes or cylinders of some description. The dimension refers to the diameter, and the diameter symbol is ∅.


• Chamfers and Countersinks :

• Counterbore :


Holes equally spaced on a pitch circle can be dimensioned as shown below


Location Dimensions :• Due to the nature of manufacturing, actual finished dimensions of manufactured components are never perfect• This has to be considered when dimensioning features that require accurate Location• In order to enable accurate measurement, such a feature is usually dimensioned from a reliable reference such as a machined surface This reference is referred to as a Datum

1. A spigot located from two reference edges

2. Two holes located from two reference edges

3. The large hole located from two reference edges and the small hole from the center of the large hole


Example ; showing that Dimensioning should match intent

• These drawings show bolts holes for mounting a flange onto a plate. • When mounting the flange, the position of the holes with respect to each other is very important, or else the flange (or part) won’t fit. • It makes sense to dimension the distance between the holes, instead of the distances to the edge

Dimensioning matches intent

Dimension placement does NOT match intent


Ballooning (Part Identification)Machines and mechanisms consists of numerous parts and a drawing which shows the complete product with all its components in their correct physical relation ship is known as an assembly drawing. A drawing which gives a small part of the whole assembly is know as a sub-assembly drawing. The method of identifying the parts in assembly/sub-assembly drawings must be clear and unambiguous in the drawing.• A parts list is a table that contains information about each of the parts contained in an assembly. The item numbers correspond with the balloon numbers• A balloon is a circle that contains a single number, which is connected to an assembly component with a leader line• Numbers in “balloons” with leader lines indicate the position of the component on the drawing• All balloons on a drawing should be the same size.• Balloons should be grouped together in an easy- to-read pattern.• Balloon numbers must correspond to item numbers in a parts list


Dimension Tolerances• In order to ensure that assemblies function properly their component parts must fit together in a predictable way • As we know, no component can be manufactured to an exact size, so the designer has to decide on appropriate upper and lower limits for each dimension• A tolerance value shows the manufacturing department the maximum permissible variation from the dimension• Accurately toleranced dimensioned features usually take much more time to manufacture correctly and therefore can increase production costs significantly.• Good engineering practice finds the optimum balance between required accuracy for the function of the component and minimum cost of manufactureIf a dimension is specified, in millimeters, as 10 ± 0.02, the part will be acceptable if the dimension is manufactured to an actual size between 9.98 and 10.02 mm

Below are some examples of ways of defining such limits for a linear dimension


Example


Example


Some examples of general tolerance notes

General tolerance notes apply tolerances to all unspecified dimensions on a drawing. They can save time and help to make a drawing less cluttered.


Limits and Fits for Shafts and Holes• Nominal size is the size by which a component is referred to as a matter of convenience, i.e. 25 mm, 50 mm, 60 mm thread• Actual size is the measured size of the finished part• Basic size is the size in relation to which all limits of size are fixed, and will be the same for both the male and female parts of the fit.• Limits of size These are the maximum and minimum permissible sizes acceptable for a specific dimension.• Zero Line It is a line along which represents the basic size and zero (or initial point) for measurement of upper or lower deviations• Tolerance This is the total permissible variation in the size of a dimension, and is the difference between the upper and lower acceptable dimensions. • Allowance concerns mating parts, and is the difference between the high limit of size of the shaft and the low limit of size of its mating hole. An allowance may be positive or negative.• Grade This is an indication of the tolerance magnitude: the lower the grade, the finer will be the tolerance• Deviation This is the difference between the maximum, minimum, or actual size of a shaft or hole and the basic size.• Upper Deviation The difference between the maximum limit of size (of either hole or shaft) and the corresponding basic size• Lower Deviation The difference between the minimum limit of size (of either hole or shaft) and the corresponding basic size• Fundamental Deviation It is one of the two deviations which is chosen to define the position of the tolerance zone• Maximum metal condition (MMC) This is the maximum limit of an external feature; for example, a shaft manufactured to its high limits would contain the maximum amount of metal. It is also the minimum limit on an internal feature; for example, a component which has a hole bored in it to its lower limit of size would have had the minimum of metal removed and remain in its maximum metal condition


Limits and Fits for Shafts and Holes• Basic size and shaft/hole tolerancing systems

The basic size or nominal size is the size of shaft or hole that the designer specifies before applying the limits to it. There are two systems used for specifying shaft/hole tolerances

Because holes are usually made with standard tools such as drills and reamers, etc, the basic hole system tends to be preferred and will therefore be used here


Fit• The fit represents the tightness or looseness resulting from the application of tolerances to mating parts, e.g. shafts and holes. • Engineering fits between two mating parts can be divided into three types:

• Clearance fit : in which the shaft is always smaller than the hole into which it fits

• Interference fit : in which the shaft is always bigger than the hole into which it fits

• Transition fit : in which the shaft may be either bigger or smaller than the hole into which it fits—it will therefore be possible to get interference or clearance fits in one group of assemblies

Clearance fits : allowance always

positive

Interference fits : allowance always

negative

Transition fits : allowance may be positive or

negative


ISO Limits and Fits : Fits have been standardized and can be taken directly from those tabulated in the BS 4500, 'ISO limits and fits.

•The BS 4500 refers to tolerance symbols made up with a letter followed by a number• COMMON HOLES : H7, H8, H9, H11• SHAFTS: c11, d10, e9, f7, g6, h6, k6, p6, s6

Remember:• Capital letters always refer to holes, lower case always refer to shafts.• The greater the number the greater or wider the tolerances

The selection of a pair of these tolerances will give you the fit. The number of possible combinations is huge. BS 4500 helps to standardize this and offers a range of fits suitable for most engineering applications

ISO limits and fits, determining working limitsConsider an example of a shaft and a housing used in a linkage:

• Type of fit: 'Normal' clearance fit.• Basic or Nominal size: ∅40mm

We will determine the actual working limits, the range of allowable sizes, for the shaft and the hole in the housing.Look along the bottom of the ISO Fits Data Sheet 4500A and locate 'Normal Fit'. We will use this pair of columns to extract our tolerances.The tolerances indicated are: 1st column H8 for the hole (upper case H)2nd column f7 for the shaft (lower case f)The actual tolerances depend upon the basic, or nominal, diameter as well as the class of fit. So, locate 40mm in the left hand Nominal Sizes column. Either the 30 - 40 or 40 - 50 range is acceptable in this case. (see table in next page)


Read across and note the tolerance values for the hole and the shaft, as shown below


For the hole diameter we have a tolerance of: +0.039mm -0.000mmFor the shaft diameter we have a tolerance of: -0.025mm -0.050mmThese tolerance values are simply added to the nominal size to obtain the actual allowable sizes.Note that this is a clearance fit. As long as the hole and shaft are manufactured within the specified tolerances the hole will always be either slightly oversize or spot on the nominal size and the shaft will always be slightly undersize. This ensures that there will always be a free clearance fit

These tolerances may be expressed on a drawing in several ways:

1) Simply as the nominal size with the tolerance class. This is not always preferred as the machine operator has to calculate the working limits

2) The nominal size with the tolerance class as above with the calculated working limits included

3) The calculated working limits only


Tabulated guide to types of ISO limits and fits


Terminology & representations of standard componentsHere are some examples of commonly used engineering components and features of components

3.5 Conventional Representations


• Screw threads Representations:

Internal thread, through: Usually drilled and tapped

Internal thread, blind: Usually drilled and tapped


• Springs:

Compression

Tension

• Knurling:

Diamond Straight



• Long Components:

Rectangular bar

Round bar

Round tube

• Shaft Ends:

Square:Frequently used for hand driven adjustments with removable handles, such as those found on machine tools, etc

Serrations:Often used for push fit components such as plastic fans or pulleys, or levers such as motorcycle gear shifters


• Gears: Bevel

Spur

Worm & Wheel


• Circlip: Internal & External

• Pins:

Split Cotter Pin:Used to lock components, prevent fasteners from coming 'un-fastened'.e.g. lock-nuts on suspension systems.

Cotter Pin:Used to retain components, usually where loads are transmitted.

Dowel Pin & Taper Pin:

Provides location, alignment


• Conventional representation of different materials in drawing


Type Convention Material

Metals

Steel, Cast Iron, Copper and its Alloys, Aluminium and its Alloys, etc.

Lead, Zinc, Tin, White-metal etc.

Glass Glass

Packing and Insulating material

Porcelain, stoneware, marble, slate etc.

Asbestos, fiber, felt, synthetic resin products, paper, cork, linoleum, rubber, leather, wax, insulating and filling material

• Conventional representation of different materials in drawing


Type Convention Material

Liquids Water, oil, petrol, kerosene etc.

Wood Wood, plywood, etc

Concrete -

Abbreviation Meaning

A/C Across cornersA/F Across flats

HEX HD Hexagon headASSY AssemblyCRS CentersCL Center line

CHAM ChamferCSK Countersunk

CBORE Counterbore

CYL Cylinder or Cylindrical

Abbreviations of terms frequently used on drawings• Abbreviations are used on drawings to save time and space. • Most of these conform to BS 8888

Abbreviation MeaningCH HD Cheese head

DIA Diameter (in a note)DP Deep (depth of bore)

Ø Diameter (preceding a dimension)

RAD Radius (in a note)

R Radius (preceding a dimension, capital only)

DRG DrawingFIG. FigureLH Left handLG Long



MATL MaterialNO. Number

PATT NO. Pattern numberPCD Pitch circle diameterI/D Inside diameterO/D Outside diameterRH Right handSCR ScrewedSPEC Specification

SPHERE SphericalSFACE Spotface

SQ Square (in a note)


TYP Typical or typicallyTHK Thick

Square (preceding a dimension)

STD StandardUCUT UndercutM/CD Machinedmm MillimeterNTS Not to scaleRPM Revolutions per minuteSWG Standard wire gaugeTPI Teeth per inch

REF ( ) Reference


Surface Finish or Surface Roughness• The quality of machined surface is characterized by the accuracy of its manufacture with respect to the dimensions specified by the designer. • Every machining operation leaves characteristic evidence on the machined surface. This evidence in the form of finely spaced micro irregularities left by the cutting tool. • Each type of cutting tool leaves its own individual pattern which therefore can be identified. • This pattern is known as surface finish or surface roughness• It is affected by the choice of tool, speed of the tool, environmental conditions, and definitely by what material you are working with

3.6 Surface Roughness

• Surface Finish Terminology

1. Roughness : Roughness consists of surface irregularities which result from the various machining process. These irregularities combine to form surface texture2. Roughness Height : It is the height of the irregularities with respect to a reference line. It is measured in millimeters or microns or micro inches. It is also known as the height of unevenness3. Roughness Width : The roughness width is the distance parallel to the nominal surface between successive peaks or ridges which constitute the predominate pattern of the roughness. It is measured in millimeters4. Roughness Width Cut Off : Roughness width cut off is the greatest spacing of respective surface irregularities to be included in the measurement of the average roughness height. It should always be greater than the roughness width in order to obtain the total roughness height rating5. Lay : Lay represents the direction of predominant surface pattern produced and it reflects the machining operation used to produce it.6. Waviness : This refers to the irregularities which are outside the roughness width cut off values. Waviness is the widely spaced component of the surface texture. This may be the result of workpiece or tool deflection during machining, vibrations or tool runout.7. Waviness Width : Waviness height is the peak to valley distance of the surface profile, measured in millimeters.

Surface Characteristics


Methods of indicating Surface Roughness for General Engineering Drawings

Basic symbolThe Basic Symbol consists of two legs of unequal length inclined at approximately 60º to the line representing the surface under consideration

Material removal through mechanical machining required

The removal of material by machining is required, a bar is added to the basic symbol as shown in the figure

Material removal not permissible

If the material removal is not permitted a circle is added to the basic symbol

The Value or Values defining the principal criterion of roughness are shown in the figure

If it is necessary to impose maximum and minimum limits of the principal criterion of roughness, both values should be shown as shown in the figure

If it is required that the final surface roughness be produced by one particular production process, this method should be indicated on an extension of the longer leg of the symbol given in the figure


Representation of Surface finish symbols in Drawing


Fastener is a hardware device that mechanically joins or affixes two or more objects together

Bolts, screws & studs: Threaded fasteners, Bolts have a shank partially threaded whereas screws are threaded along the entire length

• Threaded fastener - bolts - studs - screws

3.7 Fasteners

The last three examples here are called set screws and are used to position or lock components

3.7 Fasteners

• Screw threads: Thread TerminologyExternal (male) thread : A thread cut on the outside of a cylindrical bodyInternal (female) thread : A thread cut on the inside of a cylindrical body

Internal threadExternal thread

Internal ThreadExternal

Thread

CrestRoot

Thread angle

CrestRoot

Crest : The peak edge of a threadRoot : The bottom of the thread cut into a cylindrical bodyThread angle : The angle between threads faces

3.7 Fasteners

External Thread

Min

or d

ia.

Maj

or d

ia.

Pitch

Internal Thread

Min

or d

ia.

Maj

or d

ia.

Pitch

Pitch : The distance between crests of threadsLead : The distance a screw will advance when turned 360o

Thread that will assemble when turned clockwise.

Thread that will assemble when turned counter-clockwise.

3.7 Fasteners

Thread Form : Form is the profile shape of the thread

3.7 Fasteners

ISO (METRIC) THREAD

Externalthread

Internalthread

Center of thread assembly

60o

Pitch, P

P/4

P/8

Thread assemble occurs if and only if both (internal & external) thread have an equal nominal size (or diameter) and pitch.

3.7 Fasteners

Nominalsize

Major diameter Pitch Minor diameter Tap drill size

M6 6.00 1.00 4.92 5.00M8 8.00 1.25 6.65 6.75M10 10.00 1.50 8.38 8.50M12 12.00 1.75 10.11 10.00

METRIC COARSE THREAD

Minor diameter = Major diameter – Pitch

Minor diameter ≈ Tap drill size

Metric thread

In thread drawing, the following relationship is used.

3.7 Fasteners

Nominalsize

Major diameter Pitch Minor diameter Tap drill size

M8 8.000.75 7.188 7.251.00 6.917 7.00

M10 10.000.75 9.188 9.251.00 8.917 9.001.25 8.647 8.75

METRIC FINE THREAD

Minor diameter = Major diameter – Pitch

Minor diameter ≈ Tap drill size

In thread drawing, the following relationship is used.

3.7 Fasteners

Use local note to specify :- thread form, nominal size, pitch (if it is a fine thread)

Use typical method to specify :- thread length.

M10 ×1.5 ×1.0 Fine thread

Coarse thread

xxThreadlength

DIMENSIONING EXTERNAL THREAD

8.50 Drill, 20 Deep,M10 Tapped, 15 Deep

DIMENSIONING THREADED HOLE

3.7 Fasteners

This diagram gives approximate dimensioning methods for drawing hexagon headed metric bolts, nuts and plane washers.

(Manufacturers data sheets may give more accurate measurements.)

3.7 Fasteners

Tips for Projection of an object (Oblique & isometric)1. In an oblique method, the front side of the object is drawn to its

true shape and the side and top are drawn at an angle, typically 45º.

2. The main advantage of oblique method over isometric is the ease with which it allows us to draw circular shapes. In any type of oblique drawing, circles that face the front will appear as full circles.

3. In cavalier oblique drawings, we use the true widths of objects.4. In cabinet oblique drawings, we use half the true widths of objects.5. The receding axis of the oblique axes is typically at a 45º angle to

the horizontal.6. The easiest way to draw an object in oblique is to start with an

oblique box whose shape corresponds to the maximum length, height and width of the object.

7. Three basic rules that make it easier to draw in oblique are as follows:Rule1: Place the object so circular shapes are shown on the front.Rule2: Place the object so that the longest dimension is shown on the front.Rule3: If Rule 1 and Rule 2 conflict, Rule 1 has preference.

3.8 Drawing Tips

Tips for Projection of an object (Oblique & isometric)

• Offset coordinates are parallel lines that are used to locate the positions of points on slant edges, circles and curves.

• Isometric means equal measurement. There are equal angles (120º) between the three isometric axes.

• The easiest way to draw an object in isometric is to start with an isometric box whose shape corresponds to the longest, highest and widest measurements of the object.

• When we draw a circle in isometric it becomes an ellipse

3.8 DRAWING TIPS

Tips for Projection of an object (Orthographic) :1. Only views that clearly describe the object to be used.2. Views that show the least hidden lines should be selected.3. The object should be shown in it’s functioning position when

possible.4. The view that best describes the object should be selected as the

front view.

5. Complex part = more view, Simple part = less views

3.8 Drawing Tips

Tips for Projection of an object (Orthographic) : Conventional revolution

Feature rotation is the practice of conceptually revolving features into positions that allow them to be viewed easily in an opposing view1. For internal viewing, features may be rotated into a cutting plane2. For external viewing, features may be rotated into a principal projection plane

Internal View External ViewHole and rib rotated into cutting planeHole and rib rotated into Projection plane

3.8 Drawing Tips

1. Add sectional views to drawings of complex objects with internal surfaces to improve their clarity. This is preferable to having many hidden lines.

2. A sectional view represents the part of an object that remains after it has been cut by a cutting plane and a portion has been removed. The process of creating sectional views is known as sectioning.

3. Hatching lines are light lines which are normally drawn at a 45º angle to show that a drawing has been sectioned.

4. Use angles other than 45º for your hatching lines if the shape of the section is such that 45º lines would be parallel to one or more of its sides.

5. When sectioning two adjacent parts of an object, draw the hatching lines in opposite directions.

6. When sectioning more than two parts of an object, you may need to change the angle or width of some of the hatching lines.

Tips for Sectioning :

3.8 Drawing Tips

7. Do not draw hatching lines on assembly features and parts like bolts, dowels, keys, ribs, rivets, shafts, spokes of wheels, washers, etc, when they are truncated longitudinally. However, do draw hatching lines when these parts are cut across by a cutting plane.

8. When sectioning an object, you can bend the cutting plane to align features of an object that are at an angle to one another. This is called drawing aligned sections.

9. When sectioning an object, you can offset the cutting plane to show features that do not lie in a straight line.

10.Use an assembly drawing to show how different components of a finished product are fitted together. Most assembly drawings are sectioned.

Tips for Sectioning :

3.8 Drawing Tips

Incomplete and Missing ViewsSketch in the missing lines in the incomplete

views

3.9 Missing Views

Complete the missing view of each single solid object



Sketch an isometric pictorial for each of the objects shown in the multview drawing

Sketch an isometric pictorial for each of the objects shown in the multiview drawing

Sketch an isometric pictorial for each of the objects shown in the multiview drawing

Documents

Engineering Drawing General