Engg Drg Prctice Part 1

Engineering DRG practice

- A Refresher Course -

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Introduction:What is Engineering Drawing?

• DRG is the language of Engineers.• It is the principal means of communication in ENGG.• It is the method used to impart ideas, convey

information, specify shape, configuration and size.• It is an international language and is bound, like any

other language, by rules and conventions.




• Projections• DRG standards• Sheet sizes• Folding• Filing



Picture planes :




Projections:• Projection is the representation on a plane surface the image of

an object observed by a viewer.• In graphical language shape is described by projections as

geometric figures. • The image of the object, formed by rays of sight (lines of projection)

taken in some particular direction from the object on to a plane form a view in any DRG.




Orthographic projection:

• It is a particular type of projection in which the object’s image is

projected onto three mutually perpendicular planes.• If the viewing point (eye) is at an infinite distance from the object

such that the projection lines are parallel to one another and perpendicular to the picture plane, the projection obtained is called

Orthographic projection.

• It represents the exact shape of a three dimensional object on a two dimensional sheet in two or more views.




Orthographic projection: contd…

• These views require good imagination to interpret and visualize

the details of objects

• This method is universally used in ENGG DRG to represent objects.

• Orthographic views are required for the manufacture of objects

and machine parts.

• Front view, top view and Side view of an object are the principal

Orthographic views.

• Two types of Orthographic projections are used:

- First angle projection

- Third angle projection




First angle projection :




First angle projection :1. Object is kept above the H.P and in front of V.P. (i.e. in the

first quadrant).2. The object is projected on the V.P. and the H.P. 3. The object lies between the observer and the plane of

projection. 4. H.P. is then rotated in clockwise direction through 900 such

that the V.P. and the H.P. are brought in line with each other.5. In this projection method, the top view appears below the

front view and left side view appears on the right of the front view.




Third angle projection :




Third angle projection :1. Object is kept behind the V.P. and below the H.P. (i.e. in the

third quadrant).2. The projection plane lies between the observer and the

object.3. The projection planes are assumed to be transparent.4. The object is projected on the V.P. and the H.P. 5. H.P. is then rotated in clockwise direction through 900 such

that the V.P. and the H.P. are brought in line with each other.6. In this projection method, the top view appears above the

front view and left side view appears on the left of the front view.




Other types of projections:

• Oblique

• Isometric

• Perspective

Note: 1. Oblique and Isometric views are often used in the preparation of maintenance manuals and parts lists of ENGG equipment / assemblies.

2. Perspective views are mostly used by artists.




Other types of projections: contd…

Oblique Projection:

• It has two axes at right angles to each other.

• The third axis may be at any angle to the horizontal, 300 or 450

are being generally used.

• The measurement along the third axis are halved.




Other types of projections: contd…

Isometric Projection:

• It is a special type of pictorial projection showing the three

DIM of an object in one view.

• It conveys the real shape of the object.

• Isometric projection of any object is the single orthographic

projection of the object placed so that all its three axes are

equally inclined to the plane of projection.

• In this position, all the three sides of the object are exposed to

the viewer.

• Isometric scale = 0.815 x True length




DRG Standards




The following are some of the BIS standards relevant to Engineering DRG practice :

• These standards are reviewed and revised from time to time• IS:10714 - 1983 – General principles of presentation on technical

drawings• IS:9609 (part1)-1983 – Lettering on technical drawings (part1 English

characters)• IS:10718-1983 – Method of dimensioning and tolerancing on technical

drawings• IS:11667 – 1991 – Technical drawings - Linear and angular tolerancing

- Indication on drawings• IS:11669 -1986 – General principle of dimensioning on technical

drawings• IS:8000(Part1)-1985 - Geometrical tolerancing on technical drawings

(part 1: Tolerancing of form, orientation, location and run-out and appropriate geometrical definitions)




BIS standards for technical DRG: contd…

• IS:8000 (Part2)-1976 - Geometrical tolerancing on technical drawings (part 2: Maximum material principles)

• IS:8000 (Part3)-1985 - Geometrical tolerancing on technical drawings (part 3: Dimensioning and tolerancing of profiles)

• IS:10721 – 1983 - Datum and datum systems for geometrical tolerancing on technical drawings

• IS:11158-1984 - Proportions and dimensions of symbols for geometrical tolerancing used in technical drawings

• IS:2709-1964 - Guide for selection of fits• IS:919:1963 - Recommendations for Limits and Fits for Engg• IS:3073 -1967 - Assessment of surface roughness• IS:10719 - Method of indicating surface texture on tech DRG




BIS standards for technical DRG: contd…

• IS: 813- 1986 - Scheme of symbols for welding• IS: 10711-1983 - Sizes of DRG sheets• IS: 1064 - 1961 - Specification for paper sizes.




Sheet sizes




DRG sheet sizePreferred DRG sheet sizes are as follows:

210 X 297A4

297 X 420A3

420 X 594A2

594 X 841A1

841 X 1189A0

Trimmed size in mmSheet size


• The surface area of two successive preferred sizes are in the ratio of 1:2.• DRG sheet sides of each size are in the ratio of 1:√2• The surface area of the basic size A0 is 1 sq. m




Similarity of formats Relationship between two sides

Successive format sizes

Preferred DRG sheet sizes



Title BlockTitle block should contain the following information:1. Title of the DRG2. DRG No. & sheet No.3. Scale4. Projection symbol5. Name of the organisation6. Dated initials of the personnel designing, checking,

standard and approvedNote:

The size of the title block is uniform for all sizes.




Recommended scales for Engineering DRG:Full size Reduced scale Enlarged scale

1:1 1:2 50:11:5 20:11:10 10:11:20 5:11:50 2:11:1001:2001:5001:10001:20001:50001:10000




Grid reference on DRG sheet:

• It permits easy location on the DRG of details, additions, modifications etc.

1. How & when to use Grid reference ? eg: C7

E5




Conventional lines and applications

C1 Limits of partial or interrupted views and sections, if the limit is not a chain thin lineD1

C

D

Continuous thin free hand.Continuous thin (Straight) with zig zags.

B1 Imaginary lines of intersectionB2 DIM linesB3 Projection linesB4 Leader lines

B5 HatchingB6 Out lines of revolved section

in placeB7 Short centre line

BContinuous - thin ( Straight and curved)

A1 Visible outline A2 Visible edges

AContinuous - thick

ApplicationsLineDescription




Conventional lines and applicationsApplicationsLineDescription

J1 Indication of lines or surfaces to which a special requirement applies

J Chain thick

H1 Cutting planesHChain thin, thick at ends and changes of direction

G1 Centre linesG2 Lines of symmetryG3 Trajectories

GChain thin

E1 Hidden outlinesE2 Hidden edgesF1 Hidden outlinesF2 Hidden edges

E

F

Dashed thick

Dashed thin




Conventional lines and applications

K1 Outlines of adjacent parts

K2 Alternative and extreme positions of movable parts

K3 Centroidal linesK4 Initial outlines prior to

formingK5 Parts situated in front of

the cutting plane

KChain thin double dashed

ApplicationIllustrationType of line


• Line thicknesses recommended: 0.18, 0.25, 0.35, 0.5, 0.7, 1.0, 1.4 and 2.0

Note: Due to reproduction problems 0.18 is normally avoided



Lettering





Lettering proportions












Different characteristics of lettering type ‘A’




Different characteristics of lettering type ‘B’



DRG sheet Folding and Filing:• There are two methods of folding of DRG prints.

1. The first method is for DRG prints to be filed or bound.2. The second method is intended for prints to be kept

individually in filing cabinet.Basic principles:§ All large prints of sizes higher than A4 are folded to A4 sizes.§ The title block of a folded print as it appears in the bottom

right corner shall be visible outer most after folding.§ Suitable folding marks are to be introduced in the DRG

sheets as guide for folding purpose.





Folding of prints for filing or binding



Engineering DRG practiceFolding of prints for storing in filing cabinet



• Types of drawings• Contents of a drawing




Types of drawings1. Design layout:Shows the arrangement of various assemblies and parts in their correct orientation and location as envisaged by the designer and drawn to scale.2. Assembly drawing:Contains all the components and sub-assemblies which are shown in the correctly fitted condition and demanded item wise and number wise. The specifications for standard parts and proprietary items are also given in the assembly drawing.3. Item List:Accompanies the assembly drawings as a separate sheet/sheets. Some times this is incorporated in the assembly drawing itself.




Types of drawings4. Part drawing:Contains enough technical data to fully define the individual component and facilitate its manufacture.5. Manufacturing drawing:Contains process information for the manufacture of an assembly or individual component. It is often made as a separate drawing.In some cases process information is carried in the product drawing itself whether assembly or component.




Types of drawings6. Technical Documents:

These are strictly speaking not drawings but they come within the purview of a product design office. Some of them contain drawings /sketches in 2D or 3D form to facilitate easy understanding by the user. These include:• Product specifications• Consolidated Complete Equipment Schedule (CCES)• Operators/users manual• Maintenance/repair manuals• Illustrated Spare Parts List (ISPL)• Manufacturer’s Recommended List of Spares (MRLS)• Maintenance Scales (MS)• Training Charts




Contents of a drawing

• A DRG contains technical information in the form of Orthographic views, text and symbols.

• It gives detailed data with regard to dimensions, permissible deviations, material, surface finish, protective coatings, assembly procedures, part details, specifications, process information, etc depending upon the type of drawing.

• Drawings are made in standard sheet sizes from A4 to A0 with the title block of the organisation and numbered according to a specific system followed. The title block also contains information in type of projection method used, scale and standard notes.




Dimensions and Tolerances




Definition of Dimension : • It is a numerical value expressed in appropriate

units of measurement and indicated graphically on technical drawings with lines, symbols and notes.




Dimension Classifications:• Functional dimensions:• Any DIM that is essential for the functioning of

the component or the equipment.• Non Functional dimensions:• Auxiliary dimensions:• It does not govern production or Inspection and

is derived from other values shown on drgs.





Functional, non-functional and auxiliary DIM



System of dimensioning:1. Method 12. Method 21. Method 1 : - Aligned system• DIM values are so placed that they may be read from the

bottom or right hand edge of the DRG2. Method 2 : - Unidirectional system• DIM values are so placed that they may be read from the

bottom edge DRG sheet• It is more convenient in large size DRG




Method 1 : - Aligned system




Method 2 : - Unidirectional system




Angular dimensions




Elements of dimensioning:

1. Projection line or Extension line2. Dimensional line3. Leader line4. Dimension line termination5. The origin indication6. Dimension itself




Elements of dimensioning:




Arrangement and indication of dimensions:

1. Chain dimensioning2. Parallel dimensioning3. Super imposed running dimensioning4. Equidistant features5. Dimensioning by coordinates




Chain dimensioning




Parallel dimensioning




Super imposed running dimensioning




Equidistance feature




Dimensioning by coordinates




Addition of letters and symbols to Dimensions:Ø - DiameterR - Radius

- SquareSR - Spherical radiusSØ - Spherical diameter

Note:• The symbol should be written before the dimension




Limits, Fits and TolerancesLimits:• Limits are the two extreme permissible sizes between which

the actual size is contained.eg:30±0.02

Fit:• The relation between two parts where one is inserted into the

other with a certain degree of tightness or looseness is known as fit.




Types of fit:• Clearance fit• Interference fit• Transition fit

Clearance fit:• A positive allowance between the largest possible shaft and

the smallest possible hole.

Clearance fit- sub classifications:1. Slide fit2. Easy slide fit 3. Running fit4. Slack running fit5. Loose running fit




Interference fit:• A negative allowance or interference between the largest

possible hole and the smallest possible shaft.

Interference fit-sub classifications:1. Shrink or force fit2. Heavy drive fit3. Light drive fit

Transition fit• They cover cases between the first two classes

Condition:LL on shaft < LL on holeHL on shaft > LL on hole





Basic size, deviations and tolerances



Transition fit sub-classification:1. Force fit2. Tight fit3. Wringing fitTolerances:• Tolerance is the difference between high limit and low limit

of size.Types of tolerances:1. Bilateral tolerance:• If tolerance is applied on both sides of the basic size, then it

is called bilateral tolerance. eg:30±0.02

Tolerance = High limit - Low limit = 30.02 – 29.98 = 0.04




2. Unilateral tolerance:If tolerance is applied on one side of the basic size, then it is called Unilateral tolerance. eg:30- 0.02

Tolerance = High limit - Low limit = 30.0 – 29.98= 0.02

Allowances:• An intentional difference between the hole DIM and shaft

DIM for any type of fit is called the allowance.Deviation:• The algebraic difference between actual size and the basic

size of a component.





Disposition of tolerance zones for the three class of fit



Engineering DRG practiceDifferent methods of specifying tolerances




Different methods of specifying Fits on assembled parts

-0.020-0.041




Different methods of specifying tolerances for angular DIM



Types of deviation:• Upper deviation:• The algebraic difference between max. limit and the basic

size2. Lower deviation:• The algebraic difference between min. limit and the basic

sizeFundamental deviation:• It is one of the two deviations which is conveniently chosen

to define the position of the tolerance zone in relation to zeroline




Hole basis system:• In this system, the hole DIM (whose lower deviation is zero &

Symbol H) is kept constant and different types of fit are obtained by varying the size of the shaft.

• Most widely used

Shaft basis system:• In this system the shaft DIM (whose upper deviation is zero

& Symbol h) is kept constant and different types of fit are obtained by varying the size of the hole.





The Shaft basis and the Hole basis system



Engineering DRG practiceTolerance bands for different shafts & holes




Selection of tolerance zones



Some of the select ISO fits- Hole basis:Clearance fit:H6g5H7g6 precision runningH8g7

H6f6H7f7 close runningH8f8

H8e7H8e8 normal runningH9e9




Some of the select ISO fits- Hole basis:Clearance fit:H8d8H8d9 loose runningH9d9

H8c8 H8b8 H9c9H11c11 slack running or positional fitH11c9 H11b9




Some of the select ISO fits- Hole basis: contd…

Location and assembly fit:

H6h5 Precision locationH6h6

H7h6 Close location H7h7

H8h7 Normal location H8h8




Some of the select ISO fits- Hole basis: Location and assembly fit: contd…

H9h8 Loose location H9h9

H11h9 Slack AssyH11h11

H8h9 Positional fit




Some of the selected ISO fits- Hole basis: Transition and Interference fit:H6j5H7j6 Clearance transition H8j7

H6k5 True transition H7k6H8k7

H6m5H7m6 Interference transitionH8m7H6p5 Press fitH7p6




Standard features and components

























Welding Symbols




Welding Symbols




Welding Symbols




Welding Symbols




Standard Abbreviations



Standard AbbreviationsEngineering DRG practice

AhAmpere-hourAAmpere

BRGBearing

acAlternating current

ARRGTArrangementAPPROXApproximate

A/CAcross cornersA/FAcross flats

ALTAlteration

HBBrinell hardnessbhpBrake horse power

AUXASSY

APPD

Abbreviation

AuxiliaryAssembly

Approved

Term




CONTDContinued

CONNConnected

OceCircumference

CH HDCheese head

CPCircular Pitch

CHKDChecked

CHMEDChamfered

C/CCentre to centre

CGCentre of gravity

CLCentre line

CRSCentres

CICast iron

AbbreviationTerm





CYLCylinder / Cylindrical

DRGDrawing

dcDirect current

mm3Cubic millimetre

DIMDimension

CSK HDCountersunk head

DPDiametral Pitch

DIADiameter (in a note)

KDegree Kelvin

0CDegree Celsius

m3Cubic Metrecm3Cubic centimeter

CSKCountersunkC’BORECONSTAbbreviation

Counter boreConstant

TermStandard Abbreviations




HYDHydraulic

HDHead

etcet cetera

EEast

hHourhpHorse PowerHORZHorizontalHEXHexagon / Hexagonal

GLGround levelgGramGEN

FIG.

EXT

Abbreviation

General

Figure

External





kVAKilovolt-ampere

JJoule

kmKliometrekm/hKilometre per hour

klKilolitre

INSULInsulation

ISIndian Standard

kgfKilogram force

kWhKilowatt hourkWKilowattkVKilovolt

kgKilogram

ihpINTIDINSP

Abbreviation

Indicated Horse PowerInternalInside Diameter Inspection / Inspected





µmMicrometre

mMetre

lLitreLHLeft Hand

l/minLitres per minute

MATLMaterial

mmMillimetre

MECHMechanicalm/sMetre per second

MWMegawattMPaMega PascalMNmax.MFGM/C

Abbreviation

Mega NewtonMaximumManufacture / ManufacturingMachine / Machinery





NTSNot to scaleNNorth

minMinute (time)

mWMilliwattmVMillivolt

PaPascalODOutside diameterOPPOppositeNo.Number

NOMNominalNNewton

mMISC

min.mA

Abbreviation

ModuleMiscellaneous

MinimumMilliampere





PCDPitch Circle DiameterPCPitch Circle

sSecond (time)HRCRockwell hardness”C” scaleHRBRockwell hardness”B” scaleHRARockwell hardness”A” scaleRHRight HandrpmRevolution per minuteREQDRequiredREFReferenceRradQTYP

Abbreviation

RadiusRadianQuantityPressure

Term





SYMSymmetrical

m2Square metre

mm2Square millimetre

cm2Square centimetreSQSquare

StStokes

SFSpot faceSTDStandardSPHERE

SPECSSl No.

Abbreviation

Spherical

SpecificationSouthSerial number

Term





THKThick

WWatt

HVVickers hardness

vVelocity

volVolumeVVolt

TOLTolerance

TrTrapezoidaltTonnet

TEMP

THRUTHD

Abbreviation

Time

Temperature

Through (in a note)Thread (in a note)

Term





WRTWith respect toW

WT/m

WTWh

Abbreviation

West

Weight per metre

WeightWatt hour

Term





Materials, Heat treatment & Protective coatings




Materials

Some typical materials:1. Wrought steels:• IS:5517, IS: 2062, IS:4454• Rolled homogeneous Armour plates2. Cast steels:• IS:1030, IS:3444, IS:2856, IS:30383. Cast light alloy:• IS:617




Heat treatmentTypical notes:• Harden and temper to 32-35 HRC• Case carburise and harden gear teeth / surfaces marked

thus # to 60 - 65 HRC• Stress relieve after welding prior to machining



Engineering DRG practiceProtective Coatings

• IS:3618: 1966 – Phosphate treatment of iron and steel for protection against corrosion.

Typical note: To be phosphate treated to IS:3618, Class ‘B’Note : Class ‘B’ indicates – Medium weight 4.3 g/m2

• IS:1573:1970 - Electroplated coating on Zinc and on iron and steel

Typical note: To be Zinc plated to IS:1573, Fe Zn 40Note : Meaning of Fe Zn 40

40 – min. local thickness in micronsZn - Zinc coatingFe – Basic metal (iron or steel)

• IS: 1572-1968 – Cadmium coating on iron and steel Typical note: To be Cadmium coated to IS:1572:1970, Cd8Note : Meaning of Cd8 – min. local thick 8 microns and Average thick

12microns




Design office management




1.Purpose of design office:The creation, storage, retrieval and dissemination of

engineering information, usually pertaining to specific products/ processes.2. Relationship between Design and Drawing:

Design is the initial creative process whereby the product as envisaged is given shape, size and properties / performance on paper before physical realisation of the end product.3. Engineering DRG:

The document resulting from the design process which gives all relevant information for the manufacture / procurement of the product.






KNOWLEDGE

Physical Science

ENGG Technology

Other

SKILLS

Measurement

Graphical expression

Simulation

Experimentation

Mathematics

Management

Interactive ability

Communication

Decision making

SKILLS APPROACH

Interest

Objectivity

Open -mindedness

Creative Imagination

Product design





DRG Creation:1. Conventional drafting.• Low capital outlay• Quality and accuracy of the drawings depend upon the

individual skill and care of the human element• It is easier for the designers to visualise the product size

and configurational aspects• The DIM are not inherently related to what is drawn; hence

the probability of errors is more• Redrawing and corrections are tedious • Physical handling is more involved• More storage space is required





DRG Creation:2. Computer Aided drafting.• High capital outlay• High Quality and accuracy• It is difficult for the designers to visualise the product size

in 2D mode • The DIM are inherently related to what is drawn; hence the

probability of errors is less• Redrawing, scaling and alterations are easier • Digital storage and handling are easier and more

acceptable



Engineering DRG practiceDesign office management

Other aspects:1. DRG storage and retrieval2. DRG reproduction3. DRG numbering system4. DRG Amendments




Exercises

• DRG sheet print folding and filing

• Missing views in Orthographic DRG

• Dimensioning

• Dimensional tolerancing for specific fits

• Geometric tolerancing

• Specifying surface finish, heat treatment, protective coating,

hardness, welding, symbolic representation, materials etc.

• DRG Numbering, item No., Qty, parts list

• DRG Amendments, revision etc.




Exercise




Engineering Drawing Practice Exercise

A view from a DRG is given.

1. Is it an ASSY DRG, a Part DRG or some other type of DRG?2. Does this view give complete information of the product or not?3. Identify what it is and give a suitable nomenclature to it.4. Identify the parts in the DRG, list them out and give suitable

nomenclature to these parts.5. Sketch out one major component and identify the features on it which

require geometric tolerancing; mark the geometric tolerancing method.6. Mark all dimensions essential for the manufacture of the component.7. Identify and mark the dimensions which would require specific

tolerancing.8. Give suitable material specification with hardness/heat treatment as

applicable 9. Give surface finish recommendation where applicable for the component10.Give a step by step manufacturing process for the component









A shaft and a hole are shown in the DRG.CASE I:Dimension a = 30 mm; both materials are steel.1. Give tolerances to obtain a precision sliding fit with interchangeability.2. What is the maximum clearance in the above fit?3. What is the minimum clearance in the above fit?4. Give tolerances for a precision location fit with interchangeability.5. What is the maximum clearance in the fit mentioned in sl.No.4?6. What is the minimum clearance in the fit mentioned in sl.No.4?7. What is the maximum interference in the fit mentioned in sl.No.4?8. What is the minimum interference in the fit mentioned in sl.No.4?





A shaft and a hole are shown in the DRG.CASE II:Dimension a = 70 mm; both materials are steel.1. Give tolerances to obtain a precision sliding fit with interchangeability.2. What is the maximum clearance in the above fit?3. What is the minimum clearance in the above fit?





A shaft and a hole are shown in the DRG.CASE III:

Dimension a = 30 mm; Bore material Al. alloy and shaft steel.1. Give tolerances to obtain a precision location fit with interchangeability.2. What is the maximum clearance in the above fit?3. What is the minimum clearance in the above fit?4. What is the maximum interference in the above fit?5. What is the minimum interference in the above fit?

