quest kss engineering drawings

Aerospace Civil Structures Industrial Energy Transportation

Engineering Drawing

Prepared by : Ajitanath

QuEST, Bangalore,

© 2012, Quality Engineering and Software Technologies, Inc. All rights reserved. UNCONTROLLED WHEN PRINTED

Contents

Why Engineering Drawings?

Projections

Plan your drawing & views

Lines and line styles

Sectional views, Types & Best practice

Dimensioning

Types of dimensioning & Best practice

ISO limits and fits

Conventional representation of parts

Abbreviations of terms frequently used on drawings

Tips on Thread Assemblies

Assembly Drawings

Trend…


Why Engineering Drawings?

The main purpose of engineering drawings is to communicate to other

engineers, machinists, etc.

Engineering drawing is a formal and precise way of communicating information

about the shape, size, features and precision of physical objects. (Also specifies

material, define processes like heat treatment, surface treatment, welding specs,

etc)

Drawing is the universal language of engineering.

Just like written language has standards, the “grammar” of technical drawing is

defined by...

the ANSI Y14.5 or the ISO standard or so…

These standards must be understood to draw & read a drawing.

Drawings do the communication best merely because a picture is worth a

thousand words. Engineers are very picky about their drawings and must pay

attention to detail.


Projections

Back in the 18th century a French mathematician and engineer, Gaspard Monge

(1746-1818), was involved with the design of military armoury. He developed a

system, using two planes of projection at right angles to each other, for graphical

description of solid objects.

This system, which was,

and still is, called Descriptive Geometry.

Monge's Descriptive Geometry

forms the basis of what is now called

Orthographic Projection.

The word orthographic means to draw at right angles and is derived from the Greek

words: ORTHOS - straight, rectangular, upright

GRAPHOS - written, drawn

Projections created with the object placed in the first quadrant are

said to be in First Angle projection, and likewise, projections

created with the object placed in the third quadrant are said to

be in Third Angle projection.


Projections...

Both systems of projection, First and Third

angle, are approved internationally and have

equal status. The system used must be clearly

indicated on every drawing, using the

appropriate symbol shown in figure.

First Angle projection is more common in

Europe.

Third Angle projection is widely used in both

the USA and the UK.

Projection system symbols

and recommended

proportions


Plan your drawing & views

Before starting your engineering drawing you

should plan how you are going to make best

use of the space. It is important to think about

the number of views your drawing will have

and how much space you will use of the

paper.

Always use the appropriate & standard drawing size &

sheets.

Use recommended standard scale to the drawing.

Try to make maximum use of the available space.

Place minimum two-three appropriate views in the

planed space.

If a view has lots of detail, try and make that view as

large as possible. If necessary, draw that view on a

separate sheet.

If you intend to add dimensions to the drawing,

remember to leave enough space around the drawing

for them to be added later.


Lines and line styles

The lines we created were all of the same thickness and type. But lines on an

engineering drawing signify more than just the geometry of the object and it is

important that you use the appropriate line types.

Line Thickness : For most engineering drawings you will require two thickness', a thick and

thin line. The general recommendation are that thick lines are twice as thick as thin lines.

A thick continuous line is used for visible edges and outlines.

A thin line is used for hatching, leader lines, short centre lines, dimensions and projections.

Line Styles : Other line styles used to clarify important features on drawings are:

Thin chain lines are a common feature on engineering drawings used to indicate centre lines.

Centre lines are used to identify the centre of a circle, cylindrical features, or a line of symmetry.

Dashed lines are used to show important hidden detail for example wall thickness and holes.

etc..


Lines and line styles...

Continuous Visible outlines

0.7mm

Continuous (thin) Dimension lines

0.3mm

Short dashes Hidden detail 0.3mm

Long chain Center lines

0.3mm

Chain, thick at ends Section cutting planes

0.7 – 0.3mm

Short chain Developed views

0.3mm

Continuous wavy Broken boundaries

0.3mm

Straight zigzag Break lines 0.3mm

Straight lines with Dimension lines two short zigzags 0.3mm


Lines and line styles...

Applications of the various types of lines Some good practices


Sectional views & Types

Sectional views are produced to:

• clarify details

• show internal features clearly

• reduce number of hidden detail lines required

• aid dimensioning

• show cross-section shape

• clarify an assembly

Surfaces cut by the cutting plane are

usually hatched at an appropriate

angle, say 45° with a density of lines

in proportion with the component.

Which Sectional View?

Sectional View in a single

plane Sectional View in two

planes

Half Sectional views Part Sectional views


Sectional views & Best practice

Note:

• Revolved sections.

• Part sections.

• Different hatching directions and spacing's.

• Un-sectioned components such as shafts, keys, nuts all standard pats like motors, etc.

An assembly drawing view, clarified sections, where to hatch & hatch pattern

Wrong!

Web is not

sectioned.

Correct


Sectional views & Best practice…

The cross-section on the right of figure is technically correct. However, the convention

in a drawing is to show the view on the left as the preferred method for sectioning this

type of object.


Dimensioning

General rules.

Standards and conventions should be followed.

Dimensions should be placed on drawings so that they may be easily read.

The drawing must include the minimum number of dimensions required to accurately manufacture the design.

A dimension should not be stated more than once, unless it aids communication.

It should not be necessary for the operator manufacturing the component to have to calculate any dimensions.

Types of dimension.

Size dimensions: Used to describe heights, widths, diameters, etc.

Location dimensions: Used to place various features of a component relative to each other, such as a hole centre line to a reference surface.

Mating dimensions: Used for parts that fit together requiring a certain degree of accuracy

Dimensions have four basic components:

1. Dimension Text 2. Dimension Line and Arrows

3. Extension Lines 4. Gap


Dimensioning…

An Overview

Dimensions are always drawn

using continuous thin lines.

Two projection lines indicate

where the dimension starts

and finishes. Projection lines

do not touch the object and

are drawn perpendicular to the

element you are dimensioning.

All dimensions less than 1

should have a leading zero.

i.e. .35 should be written as

0.35

Edges A and B are being used

as the reference edges

Minimum number of

dimensions required are

specified

Evenly spaced dimension lines


Types of dimensioning

Parallel Dimensioning Superimposed Running Dimensions Chain Dimensioning

Combined Dimensions Dimensioning by Co-ordinates Simplified dimensioning by co-ordinates

Dimensioning circles


Dimensioning… & Best practice

The simple bearing bracket casting shows

both size and location dimensions

Example of appropriate and

inappropriate dimensioning


Dimensioning… & Best practice…

(D) ARROW AND TEXT PLACEMENT


Dimensioning … Which is better?


Dimensioning … Which is better?

A Dimensioning Example, showing that placement 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.

Dimension placement matches intent Dimension placement does NOT

match intent

0.753

0.747

0.756

0.744


Tabulated guide to types of ISO limits and fits.


Conventions

Conventional Breaks are a way of

depicting a very long object without

showing the entire length. It is often

used for objects like rods,

tubing/piping or wooden objects.

Here are some examples of

commonly used engineering

components and features of

components.


Conventional representation of parts


Abbreviations of terms frequently used on drawings

A/F Across flats

HEX HD Hexagon head

ASSY Assembly

CL Center line

CHAM Chamfer

CH HD Cheese head

CSK Counter sunk

CBORE Counter bore

CYL Cylinder or cylindrical

DIA Diameter (in a note)

Ø Diameter (preceding a dimension)

R Radius (preceding a dimension, capital only)

RAD Radius (in a note)

DRG Drawing

LH Left hand

MATL Material

NO. Number

PATT NO. Pattern number

PCD Pitch circle diameter

I/D Inside diameter

O/D Outside diameter

RH Right hand

SQ Square (in a note)

TYP Typical or typically

THK Thick

Square (preceding a dimension)

STD Standard

UCUT Undercut

M/CD Machined

mm Millimeter

NTS Not to scale

RPM Revolutions per minute

SWG Standard wire gauge

TPI Teeth per inch


Tips on Thread Assemblies

Note that the tapped hole is

sectioned, the fastener is not.

Observe the types of holes

& how they machined.


Assembly Drawings

The assembly of the parts is shown in an assembly drawing also known as a general

arrangement

Features of an assembly drawing

• Assembly views (with c/s views)

• Exploded views (if required)

• Dimensions

• Internal Parts

• Parts list

• Ballooning


Assembly Drawings…

Examples of Assembly Drawings


Trend…

The graph below gives a very crude indication of the productivity of companies

developing CAD software, through time.

As time passes more and more 3D CAD software packages allow you to create

high quality photorealistic images of your designs.


QuEST Recognition

Ranked 2nd among ESOs in 2006 Black Book of Outsourcing

Ranked among Top Emerging Service Providers in 2007 Global Services 100

Listed in IAOP’s 2007 Global Outsourcing 100

Listed in Deloitte’s Technology Fast 500 companies in Asia Pacific

UT500 Preferred Supplier

Supplier Excellence Award from GE

Thank you. For more information:

Presenter name: Ajitanath Patil

Title:

E: email address: [email protected]

M: contact no. 91-80-41190900

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