Geometric Symbols
ME 142 ENGINEERING DRAWING
&GRAPHICS
(Dimensioning)
LECTURE OBJECTIVES
Introduction
Dimensioning components
Dimensioning object’ s features
Placement of dimensions.
Example : Line conventions in engineering drawing
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
Basic Line Types
Types of Lines AppearanceName according
to application
Continuous thick line Visible line
Continuous thin line Dimension line
Extension line
Leader line
Dash thick line Hidden line
Chain thin line Center line
Introduction
ShapeMultiviewDrawing
Dimensioning
Designa part
1. Size, Location
ENGINEERING DESIGN
2. Non-graphic information
TRANSFERREDINFORMATION
Createdrawings
Manufacture
RESULT
Sketchesof ideas
PROCESS
DEFINITION
Dimensioning is the process of specifying part’ s
information by using of figures, symbols and notes.
This information are such as:1. Sizes and locations of features
2. Material’s type
3. Number required
4. Kind of surface finish
5. Manufacturing process
6. Size and geometric tolerances
DIMENSIONING SYSTEM
4
1
1. Metric system : ISO and JIS standards
2. Decimal-inch system
3. Fractional-inch system
8
35,
0.25 (not .25), 5.375 etc.Examples
Examples
32, 32.5, 32.55, 0.5 (not .5) etc. Examples
etc.
DimensioningComponents
DIMENSIONING COMPONENTS
Extension lines
Dimension lines(with arrowheads)
Leader lines
Dimension figures
Notes :
- local note
- general note
Drawn with
4H pencil
Lettered with
2H pencil.
indicate the location on the object’s
features that are dimensioned.
EXTENSION LINES
DIMENSION LINES
indicate the direction and extent of a
dimension, and inscribe dimension figures.
10 27
43
13123
o
indicate details of the feature with a local note.
LEADER LINES
10 27
43
13123
o
10 Drill, 2 Holes
R16
RecommendedPractices
EXTENSION LINES
Leave a visible gap (≈ 1 mm) from a view
and start drawing an extension line.
Extend the lines beyond the (last)
dimension line 1-2 mm.
Visible gapCOMMON MISTAKE
Do not break the lines as they
cross object lines.COMMON MISTAKE
Continuous
EXTENSION LINES
Dimension lines should not be spaced too close
to each other and to the view.
11 34
Leave a space at least2 times of a letter height.
16
35
DIMENSION LINES
Leave a space at least1 time of a letter height.
DIMENSION FIGURES
The height of figures is suggested to be 2.5~3 mm.
Place the numbers at about 1 mm above dimension
line and between extension lines.
COMMON MISTAKE
11
11
34
34
16.2516.25
or
DIMENSION FIGURES
When there is not enough space for figure or
arrows, put it outside either of the extension lines.
1
Not enough spacefor figures
Not enough spacefor arrows
1 1
The JIS and ISO standards adopt the unit of
Angular dimension in degree with a symbol “o”
place behind the figures (and if necessary
minutes and seconds may be used together).
DIMENSION FIGURES : UNITS
Length dimension in millimeters without
specifying a unit symbol “mm”.
1. Aligned method
2. Unidirectional method
The dimension figures are placed so that
they are readable from the bottom and
right side of the drawing.
The dimension figures are placed so that they
can be read from the bottom of the drawing.
Do not use both system on the same drawing or on the same series of drawing (JIS Z8317)
DIMENSION FIGURES : ORIENTATION
30
30
30
30
30
3030
30
EXAMPLE : Dimension of length using aligned method.
30
30
30
30
3030
30
30
EXAMPLE : Dimension of length using unidirectional method.
45 o
45 o
45o
45o
45o
45o
45o
45o
EXAMPLE : Dimension of angle using aligned method.
45o
45o
45o
45o
45o45o
45o
45o
EXAMPLE : Dimension of angle using unidirectional method.
LOCAL NOTES
Place the notes near to the feature which they
apply, and should be placed outside the view.
Always read horizontally.
10 Drill
COMMON MISTAKE10 Drill
≈ 10mm
10
Dri
ll
Too far
DimensioningPractices
THE BASIC CONCEPT
Dimensioning is accomplished by adding size and
location information necessary to manufacture
the object.
ClearComplete
Facilitate the- manufacturing method- measurement method
This information have to be
L
L
S
S
S
Designedpart
EXAMPLE
To manufacture this part we need to know…
1. Width, depth and thickness of the part.
2. Diameter and depth of the hole.
3. Location of the holes.“S” denotes size dimension.
“L” denotes location dimension.
S
L
L
ANGLE
To dimension an angle use circular dimension
line having the center at the vertex of the angle.
COMMON MISTAKE
ARCArcs are dimensioned by giving the radius, in the
views in which their true shapes appear.
R 200
The letter “R” is always lettered before the figures
to emphasize that this dimension is radius of an
arc.
R 200
or
ARCThe dimension figure and the arrowhead should
be inside the arc, where there is sufficient space.
R 200
R 62.5
Move figure outside
R 6.5
Move both figureand arrow outside
Sufficient spacefor both.
Sufficient spacefor arrowhead only.
R 58.5
Insufficient spacefor both.
ARCLeader line must be radial and inclined withan angle between 30 ~ 60 degs to the horizontal.
COMMON MISTAKE
R62.5
R62.5
R62.5
R62.5R62.5
30o
60o
R62.5
ARCUse the foreshortened radial dimension line,
when arc’ s center locates outside the sheet or
interfere with other views.
Drawing sheet
Method 1Method 2
FILLETS AND ROUNDSGive the radius of a typical fillet only by using alocal note.
R6.5
If all fillets and rounds are uniform in size,
dimension may be omitted, but it is necessary to
add the note “ All fillets and round are Rxx. ”
NOTE:All fillets and round are R6.5
Drawing sheet
R12
unless otherwise specified.NOTE:All fillets and round are R6.5
The curve constructed from two or more arcs,
requires the dimensions of radii and center’s
location.
CURVE
COMMON MISTAKE
Tangent point
CYLINDERSize dimensions are diameter and length.
Measurementmethod
Location dimension must be located from itscenter lines and should be given in circular view.
100
70
CYLINDERDiameter should be given in a longitudinal view
with the symbol “ ” placed before the figures.
HOLESSize dimensions are diameter and depth.
Location dimension must be located from its
center lines and should be given in circular view.
Measurementmethod
f xx
Use leader line and local note to specify diameter
and hole’s depth in the circular view.
HOLES : SMALL SIZE
xx Drill, Thru.
1) Through thickness hole
f xx Thru.
or
xx Drill.
or or
f xx, yy Deep
HOLES : SMALL SIZE
or
xx Drill, yy Deep
Hole’sdepth
Use leader line and local note to specify diameter
and hole’s depth in the circular view.
2) Blind hole
f xx
Use extension and dimension lines
Use diametral dimension line
Use leader line and note
HOLES : LARGE SIZE
COMMON MISTAKE
f xxf xx f xx
Rxx
f xx
HOLES
f xx
CHAMFER
Use leader line and note to indicate linear
distance and angle of the chamfer.
S
qS q
For a 45o chamfer
S SCS
or
ROUNDED-END SHAPES
R12f 12
21
5
Dimensioned according to the manufacturing
method used.
Center to Center Distance
ROUNDED-END SHAPES
R12
21
5
12
Dimensioned according to the manufacturing
method used.
Center to Center Distance
ROUNDED-END SHAPES
Dimensioned according to the manufacturing
method used.
R12
21
12
16
ROUNDED-END SHAPES
R12
27
12
Dimensioned according to the manufacturing
method used.
Tool cutting distance
ROUNDED-END SHAPES
Dimensioned according to the standard sizes ofanother part to be assembled or manufacturing method used.
25
Key(standard part)
ROUNDED-END SHAPES
Dimensioned according to the standard sizes ofanother part to be assembled or manufacturing method used.
20
Placement ofDimensions
1. Extension lines, leader lines should not cross
dimension lines.
POOR GOOD
RECOMMENDED PRACTICE
2. Extension lines should be drawn from the nearest
points to be dimensioned.
POOR GOOD
RECOMMENDED PRACTICE
3. Extension lines of internal feature can cross visible
lines without leaving a gap at the intersection point.
WRONG CORRECT
RECOMMENDED PRACTICE
4. Do not use object line, center line, and dimension
line as an extension lines.POOR GOOD
RECOMMENDED PRACTICE
POOR GOOD
5. Avoid dimensioning hidden lines.
RECOMMENDED PRACTICE
POOR GOOD
6. Place dimensions outside the view, unless
placing them inside improve the clarity.
RECOMMENDED PRACTICE
JUST OK !!! BETTER
RECOMMENDED PRACTICE 6. Place dimensions outside the view, unless
placing them inside improve the clarity.
7. Apply the dimension to the view that clearly show
the shape or features of an object.
POOR GOOD
RECOMMENDED PRACTICE
8. Dimension lines should be lined up and grouped
together as much as possible.
POOR GOOD
RECOMMENDED PRACTICE
9. Do not repeat a dimension.
POOR GOOD
RECOMMENDED PRACTICE
ME 142ENGINEERING
DRAWING&
GRAPHICS
(PROJECTION METHOD)
LECTURE OBJECTIVES
• Projection Method• Orthographic projections• Glass Box Approach• First Angle Orthographic Projection• Third Angle Orthographic Projection
PROJECTION METHOD
Perspective
Oblique Orthographic
Axonometric Multiview
Parallel
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).
Line of sight is an imaginary ray of light between an
observer’s eye and an object.
Line of sight
Parallel projection
Line of sight
Perspective projection
There are 2 types of LOS : parallel convergeand
Plane of projection is an imaginary flat plane which
the image is created.
The image is produced by connecting the points where
the LOS pierce the projection plane.
Parallel projection Perspective projection
Plane of projection Plane of projection
Disadvantage ofPerspective Projection
Perspective projection is not
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
Orthographic Projection
Orthographic Projection
5
Orthographic projection is a parallel projection technique
in which the parallel lines of sight are perpendicular to the
projection plane
MEANING
Object views from top
Projection plane
1
2
3
4
51 2 3 4
ORTHOGRAPHIC VIEWOrthographic view 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.
Multiview drawing
Axonometric drawing
Orthographic projection technique can produce either
1. Multiview drawing that each view show an object in two dimensions.
2. Axonometric drawing that show all three dimensions of an object in one view.
Both drawing types are used in technical drawing for
communication.
NOTES
ORTHOGRAPHIC VIEW
Axonometric (Isometric) Drawing
Easy to understand
Right angle becomes obtuse angle.
Circular hole becomes ellipse.
Distortions of shape and size in isometric drawing
Advantage
Disadvantage Shape and angle distortion
Example
Multiview Drawing
It represents accurate shape and size.Advantage
Disadvantage Require practice in writing and reading.
Multiviews drawing (2-view drawing)Example
Orthographic Projections
• Orthographic Projections are a collection of 2-D drawings that work together to give an accurate overall representation of an object.
Defining the Six Principal
Views or Orthographic
Views
Which Views to Present?
General Guidelines• Pick a Front View that is most descriptive of
object • Normally the longest dimension is chosen as
the width (or depth)• Most common combination of views is to use:
– Front, Top, and Side View
Glass Box Approach
• Place the object in a glass box
• Freeze the view from each direction (each of the six sides of the box) and unfold the box
Glass Box Approach
Glass Box Approach
Glass Box Approach
Glass Box Approach
Third-angle Projection
First-angle Projection
First and Third Angle Projections
• First Angle• Third Angle
ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEF
(Lettering)
ME 142ENGINEERING DRAWING
& GRAPHICS
Text on Drawings
Text 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
Example Placement of the text on drawing
Dimension & Notes
Notes Title Block
Lettering StandardANSI Standard This course
Use a Gothic text style,
either inclined or vertical.
Use all capital letters.
Use 3 mm for most
text height.
Space between lines
of text is at least 1/3
of text height.
Use only a vertical Gothic
text style.
Use both capital and
lower-case letters.
Same. For letters in title
block it is recommend to use
5~8 mm text height
N/A.
Follows ANSI rule.
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
Suggested Strokes Sequence
Straight line
letters
Curved line
letters
Curved line
letters &
Numerals
Upper-case letters & Numerals
The text’ s body height is about 2/3 the height of a capital
letter.
Suggested Strokes SequenceLower-case letters
Stroke Sequence
I L T F
E H
V X W
Stroke Sequence
N M K Z
Y A
Stroke Sequence
4
O Q C G
Stroke Sequence
D U P B
R J
Stroke Sequence
1 2
5
Stroke Sequence
7
6
8 9
0
Stroke Sequence
S 3
Stroke Sequence
l i
Stroke Sequencev w x k
z
Stroke Sequencej y f
r
t
Stroke Sequencec o a b
d p q e
Stroke Sequenceg n m h
u s
Word Composition
Look at the same word having different spacing between letters.
JIRAPONG
JI GOR NPAWhich one is easier to read ?
A) Non-uniform spacing
B) Uniform spacing
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 background
area between letters.
1. Straight - Straight
2. Straight - Curve
3. Straight - Slant
4. Curve - Curve
Space between Letters
6. Slant - Slant5. Curve - Slant
7. The letter “L” and “T”
≡ slant slant
≡slant
straight
Space between Letters
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
Leave the space between words equal to the spacerequires for writing a letter “O”.
Example
Sentence Composition
ALL DIMENSIONS ARE INMILLIMETERS
O O OOUNLESS
OTHERWISE SPECIFIED.O
ME 142ENGINEERING
DRAWING&
GRAPHICS
(Freehand Sketching)
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
Horizontal line Vertical line
Nearly verticalinclined line
Nearly horizontalinclined line
Small Circle
Method 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
Method 2 : Starting with center line
Step 1 Step 2 Step 3
1. Lightly draw a center line.
2. Add light radial lines and mark the estimated radius.
3. Sketch the full circle.
Small Circle
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
ArcMethod 1 : Starting with a square
Method 2 : Starting with a center line
Steps in Sketching
1. Block in main shape.
2. Locate the features.
3. Sketch arcs and circles.
4. Sketch lines.
Example
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