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Engineering Graphics- Basics

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Overview of an Engineering Drawing

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GRAPHICS LANGUAGE

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1. Try to write a description of this object.

2. Test your written description by having someone attempt to make a sketch from your description.

Effectiveness of Graphics Language

The word languages are inadequate for describing the size, shape and features completely as well as concisely.

You can easily understand that …

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DRAWINGS( A Graphical Representation)

The Fact about:

If compared with Verbal or Written Description,Drawings offer far better idea about the Shape, Size & Appearance of any object or situation or location, that too in quite a less time.

Hence it has become the Best Media of Communication not only in Engineering but in almost all Fields.

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Graphic language in “engineering application” use

lines to represent the surfaces, edges and contours

of objects.

A drawing can be done using freehand, instruments or computer methods.

Composition of Graphic Language

The language is known as “drawing” or “drafting” .

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Freehand drawing The lines are sketched without using instruments other than pencils and erasers.

Example

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Instrument drawing Instruments are used to draw straight lines, circles, and curves concisely and accurately. Thus, the drawings are usually made to scale.

Example

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Computer drawing The drawings are usually made by commercial software

such as AutoCAD, solid works etc.

Example

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Engineering Drawing

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Elements of Engineering Drawing

Engineering drawing are made up of graphics language

and word language.

Graphicslanguage

Describe a shape(mainly).

Wordlanguage

Describe size, location andspecification of the object.

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Basic Knowledge for Drafting

Graphicslanguage

Wordlanguage

Linetypes

Geometricconstruction Lettering

Projectionmethod

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Drawing Standard

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Standards are set of rules that govern how technical

drawings are represented.

Drawing standards are used so that drawings convey

the same meaning to everyone who reads them.

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ISO International Standards Organization

Standard Code

ANSI American National Standard InstituteUSA

JIS Japanese Industrial StandardJapan

BS British StandardUK

AS Australian StandardAustralia

Deutsches Institut für NormungDINGermany

Country Code Full name

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Drawing Sheet

Trimmed paper ofa size A0 ~ A4.

Standard sheet size (JIS)

A4 210 x 297A3 297 x 420A2 420 x 594A1 594 x 841A0 841 x 1189

A4

A3

A2

A1

A0(Dimensions in millimeters)

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Drawing Scales

Designation of a scale consists of the word “SCALE”

followed by the indication of its ratio, as follow

SCALE 1:1 for full size

SCALE X:1 for enlargement scales

SCALE 1:X for reduction scales

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Basic Line Types

Types of Lines Appearance Name accordingto application

Continuous thick line Visible line

Continuous thin line Dimension lineExtension lineLeader line

Dash thick line Hidden line

Chain thin line Center line

NOTE : We will learn other types of line in later chapters.Engineering108.com

Visible lines represent features that can be seen in the

current view

Meaning of Lines

Hidden lines represent features that can not be seen in the current view

Center line represents symmetry, path of motion, centers of circles, axis of axisymmetrical parts

Dimension and Extension lines indicate the sizes and location of features on a drawing

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Example : Line conventions in engineering drawing

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Traditional Drawing Tools

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DRAWING TOOLS

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1. T-Square 2. Triangles

DRAWING TOOLS

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3. Adhesive Tape 4. Pencils

2H or HB for thick line4H for thin line

DRAWING TOOLS

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5. Sandpaper 6. Compass

DRAWING TOOLS

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7. Pencil Eraser 8. Erasing Shield

DRAWING TOOLS

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9. Circle Template 10. Tissue paper

DRAWING TOOLS

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11. Sharpener 12. Clean paper

DRAWING TOOLS

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Lettering

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Text on DrawingsText on engineering drawing is used :

To communicate nongraphic information.

As a substitute for graphic information, in those instance where text can communicate the needed information more clearly and quickly.

Uniformity - size- line thickness

Legibility - shape- space between letters and words

Thus, it must be written with

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Example Placement of the text on drawing

Dimension & Notes

Notes Title BlockEngineering108.com

Lettering StandardANSI Standard This course

Use a Gothic text style,either inclined or vertical.

Use all capital letters.

Use 3 mm for mosttext height.

Space between linesof text is at least 1/3of text height.

Use only a vertical Gothictext style.

Use both capital andlower-case letters.

Same. For letters in title block it is recommend to use 5~8 mm text height

N/A.Follows ANSI rule.

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Stroke SequenceI L T F

E H

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V X W

Stroke Sequence

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N M K Z

Y A

Stroke Sequence

4

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O Q C GStroke Sequence

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D U P B

R J

Stroke Sequence

1 2

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5

Stroke Sequence

7

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6

8 9

0Stroke Sequence

S 3

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Stroke Sequence

l i

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Stroke Sequencev w x k

z

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Stroke Sequencej y f

r

t

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Stroke Sequencec o a b

d p q e

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Stroke Sequenceg n m h

u s

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GOOD

Not uniform in style.

Not uniform in height.

Not uniformly vertical or inclined.

Not uniform in thickness of stroke.

Area between letters not uniform.

Area between words not uniform.

Example : Good and Poor Lettering

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Leave the space between words equal to the spacerequires for writing a letter “O”.

Example

Sentence Composition

ALL DIMENSIONS ARE INMILLIMETERS

O O OO UNLESS

OTHERWISE SPECIFIED.O

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1. Place the little finger (or pencil’ s tip) at the center as a pivot, and set the pencil point at the radius-distance from the center.

2. Hold the hand in this position and rotate the paper.

Large Circle

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♣ The following figures illustrates the Aligned system of dimensioning:

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QUADRANT THEORY

FRP/V.P.

HRP/ H.P.

FRONTDIRECTION

X

YI

II

IIIIV

FOUR QUADRANTS

TOPDIRECTION

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X

Y

1ST Quad.2nd Quad.

3rd Quad. 4th Quad.

X Y

VP

HP

Observer

THIS QUADRANT PATTERN, IF OBSERVED ALONG X-Y LINE ( IN RED ARROW DIRECTION)WILL EXACTLY APPEAR AS SHOWN ON RIGHT SIDE AND HENCE,IT IS FURTHER USED TO UNDERSTAND ILLUSTRATION PROPERLLY.

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♣ How to fold the A2 size drawing sheets for assignment work?♥ Mark 190 mm from the right edge of the drawing sheet. Mark 186 mm from the previous mark. Mark 20

mm from the left edge of the drawing sheet.♥ Mark 297 mm from the bottom edge of the drawing sheet on the reverse side. ♥ Coincide the first fold with third fold to get second fold. Coincide the third fold with the border line which

is 20 mm to the right of left edge of drawing sheet to get fourth fold. Fifth and sixth folds are back folds. ♥ All larger size drawing sheets i.e. A0, A1, A2 and A3 are folded to A4 size sheet.

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