Geometric Symbols. ME 142 ENGINEERING DRAWING & GRAPHICS (Dimensioning)

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


method used.

Center to Center Distance

ROUNDED-END SHAPES


method used.

R12

21

12

16

ROUNDED-END SHAPES

R12

27

12


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


3. Extension lines of internal feature can cross visible

lines without leaving a gap at the intersection point.

WRONG CORRECT


4. Do not use object line, center line, and dimension

line as an extension lines.POOR GOOD


POOR GOOD

5. Avoid dimensioning hidden lines.


POOR GOOD

6. Place dimensions outside the view, unless

placing them inside improve the clarity.


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


8. Dimension lines should be lined up and grouped

together as much as possible.

POOR GOOD


9. Do not repeat a dimension.

POOR GOOD


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

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

Geometric Symbols. ME 142 ENGINEERING DRAWING & GRAPHICS (Dimensioning)

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Transcript of Geometric Symbols. ME 142 ENGINEERING DRAWING & GRAPHICS (Dimensioning)