Chapter 01 Introduction To Engineering Drawing
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Transcript of Chapter 01 Introduction To Engineering Drawing
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Chapter 1Overview of an
Engineering Drawing
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TOPICS
Drawing standards
Projection methods
Orthographic projection
Graphics language
Engineering drawing
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TOPICS
Traditional Drawing Tools
Freehand Sketching
Lettering
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GRAPHICSLANGUAGE
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1. Try to write a description ofthis object.
2. Test your written description
by having someone attemptto make a sketch from yourdescription.
Effectiveness of Graphics Language
The word languages are inadequate for describing thesize , shape and features completely as well asconcisely.
You can easily understand that
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Graphic language in engineering application usel ines to represent the surfaces , edges and con tou r s
of objects.
A drawing can be done using freehand , in s t rumen ts or co m p u te r methods.
Composition of Graphic Language
The language is known as drawing or draf t ing .
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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 areusually 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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EngineeringDrawing
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Elements of Engineering Drawing
Engineering drawing are made up of graphics lang uageand wo rd langu age .
Graphicslanguage
Describe a shape(mainly).
Wordlanguage
Describe size, location and
specification of the object.
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Basic Knowledge for Drafting
Graphics
language
Word
language
Linetypes
Geometricconstruction Lettering
Projectionmethod
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PROJECTIONMETHOD
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PROJECTION METHOD
Perspective
Oblique Orthographic
Axonometric Multiview
Parallel
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PROJECTION THEORY
The projection theory is based on two variables:
1) Line of sight
2) Plane of projection (image plane or picture plane)
The projection theory is used to graphically represent
3-D objects on 2-D media (paper, computer screen).
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Plane of projection is an imaginary flat plane whichthe image is created.
The image is produced by connecting the points where
the LOS pierce the projection plane.
Paral lel pro ject ion Persp ect ive pro ject ionPlane of projection Plane of projection
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Disadvantage ofPerspective Projection
Perspective projection is n o t
used by engineer for manu-
facturing of parts, because
1) It is difficult to create.
2) It does not reveal exact
shape and size.Width is distorted
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OrthographicProjection
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5
Orthographic projection is a parallel projection techniquein which the parallel lines of sight are perpendicu lar to the
projection plane
MEANING
Object views from top
Projection plane
1
2
3
4
5 1 2 3 4
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ORTHOGRAPHIC VIEWOrthograph ic v iew depends on relative position of the object
to the line of sight.
Two dimensions of anobject is shown.
Three dimensions of an object is shown.
Rotate
Tilt
More than one view is neededto represent the object.
Mult iv iew drawing
Axo nom et r ic d rawing
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Orthographic projection technique can produce either
1. Mult iv iew drawing
that each view show an object in two dimensions.2. Axo nom et r ic d rawing
that show all three dimensions of an object in one view.
Both drawing types are used in technical drawing forcommunication.
NOTES
ORTHOGRAPHIC VIEW
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Axonometric (Isometric) Drawing
Easy to understand
Right angle becomes obtuse angle.
Circular holebecomes ellipse.
Distortions of shape and size in isometric drawing
Advantage
Disadvantage Shape and angle distortion
Example
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Drawing Standard
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Introduction
Standards are set of rules that govern how technicaldrawings are represented.
Drawing standards are used so that drawings conveythe same meaning to everyone who reads them.
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ISO International S tandards Organization
Standard Code
ANSI American National S tandard InstituteUSAJIS J apanese Industrial S tandardJapan
BS British S tandardUK
AS Australian S tandard AustraliaDeutsches Institut f r NormungDINGermany
Country Code Full name
. Thailand
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Partial List of Drawing Standards
. 210 2520 :
. 440 .1 2541 1
. 446 .4 2532
. 1473 2540
Code number Contents
: http://library.tisi.go.th/data/lib_resources/pdf/catalog-online49/tis/02_ICS.pdf
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Partial List of Drawing Standards
JIS Z 8311 Sizes and Form at of Draw ing s
JIS Z 8312 Line Convent ions
JIS Z 8313 Letter ing
JIS Z 8314 Scales
JIS Z 8315 Projection methods
JIS Z 8316 Presentation of Views and SectionsJIS Z 8317 Dimensioning
Code number Contents
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Drawing Sheet
Trimmed paper ofa size A0 ~ A4.
Standard sheet size (JIS )
A4 210 x 297 A3 297 x 420 A2 420 x 594
A1 594 x 841 A0 841 x 1189
A4
A3
A2
A1
A0(Dimensions in millimeters)
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Drawing space Drawingspace
Title block
d
d
c
c
cBorderlines
1. Type X (A0~A4) 2. Type Y (A4 only)
Orientation of drawing sheet
Title block
Sheet size c (min) d (min)
A4 10 25 A3 10 25 A2 10 25 A1 20 25
A0 20 25
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Drawing Scales
Scale is the ratio of the linear dimension of an elementof an object shown in the drawing to the real linear
dimension of the same element of the object.
Size in drawing Actual size
Length, size
:
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Drawing ScalesDesignation 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 (X > 1)SCALE 1: X for reduct ion scales (X > 1)
Dimension numbers shown in the drawing are correspond
to true size of the object and they are independent of
the scale used in creating that drawing.
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Basic Line Types
Types of Lines AppearanceName according
to application
Continuous thick line Visible line
Continuous thin line Dimension lineExtension line
Leader line
Dash thick line Hidden line
Chain thin line Center line
NOTE : We will learn other types of line in later chapters.
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Visib le l ines represent features that can be seen in thecurrent view
Meaning of Lines
Hidden l ines represent features that can not be seen in
the current view
Center lin e represents symmetry, path of motion, centers
of circles, axis of axisymmetrical parts
Dim ens ion and Extens ion l ines indicate the sizes and
location of features on a drawing
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Example : Line conventions in engineering drawing
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TraditionalDrawing Tools
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DRAWING TOOLS
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3. Adhesive Tape 4. Pencils
H or HB for thick line
4H 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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ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLM
NOPQRSTUVWXYZABCDEF
ABCDEFGHIJKLMNOPQRST
UVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEF
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 instancewhere text can communicate the needed information
more clearly and quickly.
Unifo rmi ty - size- line thickness
Legib i l i ty - shape- space between letters and words
Thus, it must be written with
l
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Example Placement of the text on drawing
Dimension & Notes
NotesTitle Block
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Basic Strokes
Straight Slanted CurvedHorizontal
1 1 2
3
Examples : Application of basic stroke
I letter A letter 1
2
3
4 5
6
B letter
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Suggested Strokes Sequence
Straight lineletters
Curved lineletters
Curved lineletters &Numerals
Upper-case letters & Numerals
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Stroke Sequence
I LT
F
E H
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N M K Z
Y A
Stroke Sequence
4
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OQ C G
Stroke Sequence
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S k S
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6
8 9
0 Stroke Sequence
S 3
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S k S
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Stroke Sequencev w x k
z
S k S
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Stroke Sequence j y f
r
t
S k S
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Stroke Sequencec o a b
d p q e
St k S
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Stroke Sequenceg n m h
u s
W d C iti
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Word CompositionLook at the same word having different spacing between letters.
JIRAPONGJ I GOR NP A
Which one is easier to read ?
A) Non-uniform spacing
B) Uniform spacing
Word Composition
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Word Composition
JIRAPONG \ / \ | )( ) | ( |
Space between the letters depends on the contour of
the letters at an adjacent side.
Spacing
Contour | | | | General conclusions are:
Good spacing creates approximately equal b ack g ro u n d
area between letters.
Space between Letters
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1. Straight - Straight
2. Straight - Curve
3. Straight - Slant
4. Curve - Curve
Space between Letters
Space between Letters
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6. Slant - Slant5. Curve - Slant
7. The letter L and T
slant slant
slant
straight
Space between Letters
Example : Good and Poor Lettering
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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
Sentence Composition
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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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FreehandSketching
Straight Line
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Straight Line
1. Hold the pencil naturally.
2. Spot the beginning and end points.
3. Swing the pencil back and forth between the points, barely
touching the paper until the direction is clearly established.
4. Draw the line firmly with a free and easy wrist-and-arm
motion
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Horizon tal l ine Vertic al l ine
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Nearly vert ic alinc l ined l ine
Nearly h or izo n talinc l ined l ine
Small Circle
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Small CircleMethod 1 : Starting with a square
1. Lightly sketching the square and marking the mid-points.
2. Draw light diagonals and mark the estimated radius.
3. Draw the circle through the eight points.
Step 1 Step 2 Step 3
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Large Circle
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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 fromthe center.
2. Hold the hand in this position and rotate the paper.
Large Circle
Arc
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ArcMethod 1 : Starting with a square
Method 2 : Starting with a center line
Steps in Sketching
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Steps in Sketching
1. Block in main shape.
2. Locate the features.
3. Sketch arcs and circles.
4. Sketch lines.
E l
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Example