Computer Aided Design - Lecture 01

8/2/2019 Computer Aided Design - Lecture 01

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Technical Graphics

The accurate representation of an object for technical and architectural purposes

The art and practice of creating technical graphics is called Engineering/TechnicalDrawing



TYPES OF TECHNICAL GRAPHICS

Two basic types of graphic representations:

Pictorial Representation include drawings & paintings of

objects e.g. Murals of ancient Rome

T extual Representation includes graphic symbols (languages

except Chinese and Japanese) e.g. Alphabets, Numbers etc.

Note: The best way to communicate is to combine both Pictorial

and Textual (Language, Speech and Graphics)



Applications of Technical Graphics

Communicating concepts/ideas:

³A picture is worth more than a thousand words´

Technical dra

wing c

onveys in

for m

atio

n abo

ut ano

bjectf r om

thedesigner to the manuf acturer so that the concept f r om someone¶shead be actualized

Need graphic communication in design cycle

A new concept/idea must be pr operly communicated thr oughgraphic representation for all those involved in the developmentpr ocess.



V isualization

Technical Graphics help easier visualization e.g.

I need you to design a baby a baby doll. Imagine

the following specif ications

1. Baby girl

2. Blue eyes

3. Red sleeveless shirt

4. Laughing

5. Both ar ms raised upwards etc.

Make a Picture in your mind and remember that....



Did you imagine that I want this«..?



V isualization

Similarly a new pr oduct being engineered

goes thr ough the pr ocess of Concept,

Design, Analysis, Revisions (if required) and

then implementation

The person who f irst conceives the pr oduct

needs technical drawing of it for others to

visualize exactly what he thinks Labelled map is another example



Engineering Analysis

A pr oduct test at design stage is much cost-

eff ective than building the entire object and

learning about the f law af ter it is launched

CAD allows pr oduct testing at design stage

Observations are recorded for analysis and

f urther enhancements/revisions



Documentation

A technical drawing of a pr oduct/object is a

record document as other off icial documents

about the pr oduct design. It includes

Bill of materials

Special Notes

Dates (revision tracks) Company name etc.



Elements of Technical Drawings

Conventions

Unwritten rules followed over a long period of time

and adopted as standard part of draf ting language

Should be common and understood by all who

read/use or create these drawings



Drawing Conventions

Title Block

Placed at the bottom

-right corner

Includes company name, logo, sheet number,

pr oduct/part name and review details



Drawing Conventions

Drawing Layout

Appr opriate (Standard) sheet size/standard templates (inCAD)

Single Unit Measurement/Scale must be used thr oughoutthe drawing

Any deviations must be clearly mentioned

Bill of materials should appear at the right of the drawingarea above the title block



Drawing Conventions

2D Modelling

Each draw

ing includes detailsof

part andassembly drawings which are communicated

thr ough 2D drawings (Lettering)



Drawing Conventions

Part Details

Diff erent views of the various parts are detailed

with textual drawings for f abricator to understand

what a particular part looks like. Part detailsinclude

Title, shape, size, material related info etc



Drawing Conventions

Assembly Drawing

Depict the total assembly of diff erent parts of the

complete pr oduct and the manuf acturing pr ocess

Shows which part f its where, how and the pr oduct

can be assembled in what sequence (Numbered)



Scaling

Enlarging/Reducing

the real time measures to

adjust into drawing

space/area

Scaling Ratios

Full Scale Drawings (1:1)

Reduced Scale Drawings (1:5) (Scaling Down)

Enlarged Scale Drawings (5:1) (Scaling Up)

Drawing Conventions



User Coordinate System (UCS)

Space ar ound us is inf inite

Location of any object/point is def ined relative to a

ref erence point called origin

One horizontal and one vertical lines are chosen asX,Y axis and their intersection is considered asorigin

of the C

oordinate syste

m

AutoCad def ines a def ault CS which might bechanged if desired/required



Lines Building block of technical graphics

Used for drawing objects, lettering and dimensioning

Characteristics of Lines

Thickness

Continuity

The style of discontinuity

Colour

Texture

A combination of diff erent characteristics represent diff erent types of lines

giving diff erent meanings which have been standardized (ANSI, ISO) so thatall the draf ters speak the same language for better understanding



Types of Lines

Diff erent types of lines impr ove readability of

the drawing and help it communicate more

eff ectively and eff iciently

Each line type has a unique syntax and

application



Types of Lines

Visible Lines:

Most important

Show basic shape and outline of an object

(All other types show object details)

Show its edges and def ine its sur f ace boundaries Its ³THICK´ & ³CONTINOUS´

Hidden Lines

Show those f eatures of the pr oduct that are not directly visible

Example of hole in a box Medium thickness dashed lines



Types of Lines

Dimension Lines Show an objects length, breadth, height, radius, diameter and angle

Continuous thin line with arr ow heads or dashes at both the ends

Conventions vary for dimension lines for various engineering disciplines



Section Fill Lines

Used to show section of an object been cut thr ough to

show additional/internal details

Generally (if not showing material) these lines are thin,continuous, parallel, unifor mly spaced and generally

inclined at 45o(30oor 60o in some special cases)

Line at the edges of the section lines is kept thicker for

distinguishm

ent purpose

There are diff erent international standards to use

section lines to represent diff erent materials



Types of Lines

Centre Line Thin line consisting of alternating long and short

dashes

Start and end with long dashes

Used to indicate the symmetry of an object They intersect at short dashes (& in best practice

at the center

e.g. Two center lines intersecting at right angle to

each other depict the circular symmetry



Types of Lines

Cutting plane lines

Alternating long and short dashes but thick at the

ends

Having arr ow-heads drawn at right angle (90o) at

both the ends

These lines show the cutting plane that is used to

section/cut the object to view the internal hidden

details

Arr ow head show the direction f r om which the

section be viewed



Types of Lines

Break Lines

Short Break Lines

Thick f reehand line to show irregular shape over short span of distance

Long Break Lines

Thin f reehand zigzag line

Use: used to show an area or a portion of a part that hasbeen removed to show hidden details, to limit a partialsection or view and to eliminate repeated details



Types of Lines

Construction Lines

Faint lines (barely visible) used to construct

object¶s graphics between two views

One of the views/positions of the object may beshown be dotted lines

These lines are usually not shown in f inal

drawings

Manual draf ters mostly use special blue pencil

that¶s not visible in f inal draf t



Types of Lines

Extension Lines

Thin continuous line that does not touch the

visible line/outline

Use: to extend points or planes to indicatedimensional limits



Precedence of Lines

Technical drawings use variety of line types

Diff erent line types may coincide or appear behind one

ano

ther

For better visualization and understanding thefollowing precedence rule be followed;

Visible lines takes precedence over all other types Hidden Lines take precedence over center lines Cutting plane lines take precedence over center lines

Documents

Computer Aided Design - Lecture 01