chapter 2: dimensioning -...

Copyright ©2006 by K. Plantenberg

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Chapter 2:

Dimensioning

Basic Topics

Advanced Topics

Exercises


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Dimensioning: Basic Topics

Summary

2-1) Detailed Drawings

2-2) Learning to Dimension

2-3) Dimension Appearance and Techniques.

2-4) Dimensioning and Locating Simple

Features.

2-6) Dimension Choice.


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Dimensioning: Advanced Topics

2-5) Dimensioning and Locating Advanced

Features.


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Dimensioning: Exercises

Exercise 2-1: Dimension type

Exercise 2-2: Spacing and readability 1

Exercise 2-3: Spacing and readability 2

Exercise 2-4: Duplicate dimensions

Exercise 2-5: Dimension placement

Exercise 2-6: Circular and rectangular views

Exercise 2-7: Dimensioning and locating features

Exercise 2-8: Advanced features

Exercise 2-9: Dimension accuracy

Exercise 2-10: Round off


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Dimensioning: Exercises

Exercise 2-11: Dimension choice

Exercise 2-12: Dimensioning 1





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Dimensioning

Summary


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Dimensioning Summary

� What will we learn in Chapter 2?

→ How to dimension an orthographic

projection using proper dimensioning

techniques.

� Key points

→ Dimensions affect how a part is

manufactured.


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Dimensioning

2-1) Detailed Drawings


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Detailed Drawings

� Orthographic Projection: A shape

description of an object (front, top, right

side views).

� Detailed Drawing: An orthographic

projection, complete with all the

dimensions and specifications needed to

manufacture the object.


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Detailed Drawing Example


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Detailed Drawings

� Can we dimension an object using the

dimensions that we used to draw the

object?

No

These are not necessarily the same

dimensions required to manufacture it.

We need to follow accepted standards.

(ASME Y14.5 – 1994)


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Dimensioning

2-2) Learning To Dimension


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Learning to Dimension

� What is our goal when dimensioning a

part?

→ Basically, dimensions should be given in a

clear and concise manner and should

include everything needed to produce and

inspect the part exactly as intended by the

designer.


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� Proper dimensioning techniques

require the knowledge of the following

three areas.

→ Dimension Appearance/Technique

→ Dimensioning and Locating Features

→ Dimension Choice


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1. Dimension Appearance/Technique:

Dimensions use special lines, arrows,

symbols and text.

a) The lines used in dimensioning.

b) Types of dimensions.

c) Dimension symbols.

d) Dimension spacing and readability.

e) Dimension placement.


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2. Dimensioning and Locating Features:

Different types of features require unique

methods of dimensioning.


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3. Dimension Choice: Your choice of

dimensions will directly influence the

method used to manufacture the part.

a) Units and decimal places.

b) Locating feature using datums.

c) Dimension accuracy and error build up.


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Dimensioning

2-3) Dimension Appearance

and Techniques


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Lines used in Dimensioning

� Dimensioning requires the use of

→ Dimension lines

→ Extension lines

→ Leader lines

� All three line types are drawn thin so that

they will not be confused with visible lines.


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Dimension Line

� Dimension line: A line terminated by

arrowheads, which indicates the direction

and extent of a dimension.


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Extension Line

� Extension line: An extension line is a

thin solid line that extends from a point on

the drawing to which the dimension refers.

Long extension

lines should be

avoided.


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Leader Line

� Leader Line: A straight inclined thin solid

line that is usually terminated by an

arrowhead.


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Leader Line

� Leaders may be terminated:

→ with an arrow, if it ends on the outline of an

object.


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Leader Line


→ with a dot if it ends within the outline of an

object.


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Leader Line


→ without an arrowhead or dot, if it ends within

the outline of an object.


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Leader Line

� Avoid!

→ Crossing leaders.

→ Long leaders.

→ Leaders that are parallel to adjacent

dimension, extension or section lines.

→ Small angles between the leader and the

terminating surface.


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Arrowheads

� Arrowheads are drawn between the

extension lines if possible. If space is

limited, they may be drawn on the outside.


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Types of Dimensions

� Dimensions are given in the form of

linear distances, angles, and notes.

→ Linear distances: They are usually

arranged horizontally or vertically, but may

also be aligned with a particular feature of

the part.


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Types of Dimensions



→ Angles: Used to give the angle between

two surfaces or features of a part.


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Types of Dimensions



→ Notes: Used to dimension diameters, radii,

chamfers, threads, and other features that

can not be dimensioned by the other two

methods.


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Exercise 2-1

Dimension types


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Exercise 2-1

� Count the different types of dimensions.

→ How many linear horizontal dimensions are

there? 5


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Exercise 2-1


→ How many linear vertical dimensions are

there? 3


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Exercise 2-1


→ How many angular dimensions are there? 1


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Exercise 2-1


→ How many leader line notes are there? 1


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Lettering

� Lettering should be legible, easy to

read, and uniform throughout the

drawing.

→ Upper case letters should be used for all

lettering unless a lower case is required.

→ The minimum lettering height is 0.12 in (3

mm).


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Dimensioning Symbols

� Dimensioning symbols replace text.

→ The goal of using dimensioning symbols is to

eliminate the need for language translation.

� Why is it important to use symbols.

→ How many products are designed in the

United States?

→ How many products are manufactured or

assembled in the United States?


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Term Symbol

Diameter nnnn

Spherical diameter Snnnn

Radius R

Spherical radius SR

Reference dimension (8)

Counterbore / Spotface vvvv

Countersink wwww

Number of times or places 4X


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Term Symbol

Depth / Deep xxxx

Dimension not to scale 10

Square (Shape) oooo

Arc length

Conical Taper yyyy

Slope zzzz

Symmetry iiii

5)


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Spacing and Readability

� Dimensions should be easy to read,

and minimize the possibility for

conflicting interpretations.


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a) The spacing between dimension lines

should be uniform throughout the

drawing.

b) Do not dimension inside an object or

have the dimension line touch the object

unless clearness is gained.


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c) Dimension text should be horizontal

which means that it is read from the

bottom of the drawing.

d) Dimension text should not cross

dimension, extension or visible lines.


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Exercise 2-2

Spacing and Readability 1


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Exercise 2-2

� List the dimensioning mistakes and then

dimension the object correctly.

What are the 6 dimensioning mistakes?

1) Spacing

6) Missing dim. (nnnn of hole)

3 & 4) Text

5) No Gap

2) Don’t dim. inside the object.

Correctly Dimensioned


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e) Dimension lines should not cross

extension lines or other dimension lines.

→ Extension lines can cross other extension

lines or visible lines.

f) Extension lines and centerlines should

not connect between views.


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g) Leader lines should be straight, not

curved, and point to the center of the arc

or circle at an angle between 30o – 60o.


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Exercise 2-3

Spacing and Readability 2


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Exercise 2-3



3) Text

2) Center line

4) Crossing dim.

and ext. line

1) Leader line


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h) Dimensions should not be duplicated or

the same information given in two

different ways.

→ If a reference dimension is used, the size

value is placed within parentheses (e.g.

(10) ).


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Exercise 2-4

Duplicate dimensions


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Exercise 2-4

� Find the

duplicate

dimensions and

cross out the

ones that you

feel should be

omitted.

Are there any duplicates

in this group?Which one

shouldbe omitted?


in this group?Which ones

shouldbe omitted?


in this group?Which one

shouldbe omitted?


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Dimension Placement

� Dimensions should be placed in such a

way as to enhance the communication

of your design.


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Dimension Placement

a) Dimensions should be grouped

whenever possible.

b) Dimensions should be placed between

views, unless clearness is promoted by

placing some outside.


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Dimension Placement

c) Dimensions should be attached to the

view where the shape is shown best.

d) Do not dimension hidden lines.


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Exercise 2-5

Dimension placement


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Exercise 2-5

� List the

dimensioning

mistakes and

then

dimension the

object

correctly.

What are the 6

dimensioning

mistakes?

1) Between views

2) Leaders

angle up

3) Don’t dim.

Hidden lines

4) Dim where

feature shown

best

6) Long

ext. line

5) Group


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Dimensioning

2-4) Dimensioning and

Locating Simple Features


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Dimensioning Features

a) A circle is dimensioned by its diameter

and an arc by its radius using a leader

line and a note.


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Exercise 2-6

Circular and rectangular views


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Exercise 2-6

� Answer questions

about the cylindrical

and hole features of

the part shown.

Find the hole and

cylinder.

Which view is

considered the circular

view and which is

considered the

rectangular view?

Circular view

Rectangular view

Looking at just the

top view, can you

tell the difference

between the hole

and the cylinder?

No

So that the cylinder

is not confused with

a hole.

Why is the diameter

of the hole given in

the circular view and

diameter of the

cylinder given in the

rectangular view?


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b) Holes are

dimensioned by

giving their

diameter and

location in the

circular view.


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c) A cylinder is

dimensioned by

giving its diameter

and length in the

rectangular view,

and is located in

the circular view.


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d) Repetitive features or dimensions may

be specified by using the symbol “X”

along with the number of times the

feature is repeated.

→ There is no space between the number of

times the feature is repeated and the “X”

symbol, however, there is a space between

the symbol “X” and the dimension.


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Exercise 2-7

Dimensioning and locating

features


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Exercise 2-7

� Dimension the object shown.

How do we dimension the hole diameters?

How do we locate the holes?

How do we dimension the cylinder diameters?

How do we dimension the cylinder heights?

Completely dimensioned.


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Dimensioning

2-5) Dimensioning and

Locating Advanced Features

Skip advanced topic


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a) If a dimension is given to the center of a

radius, a small cross is drawn at the

center.


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a) Where the center location of the radius is

unimportant, the drawing must clearly

show that the arc location is controlled by

other dimensioned features such as

tangent surfaces.


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b) A complete sphere is dimensioned by its

diameter and an incomplete sphere by its

radius.


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c) The depth of a blind hole may be

specified in a note and is the depth of the

full diameter from the surface of the

object.


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d) If a hole goes completely through the

feature and it is not clearly shown on the

drawing, the abbreviation “THRU” follows

the dimension.


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e) If a part is symmetric, it is only necessary

to dimension to one side of the center

line of symmetry.

Symmetry

symbol


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f) Counterbored holesDrill DIA

C’Bore DIA

C’Bore depth


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f) If the thickness of the material below the

counterbore is significant, this thickness

rather than the counterbore depth is

given.


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Application Question 2-1

� What do you think a counterbored hole is

used for?


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g) Spotfaced Holes: The difference between

a C’BORE and a Spotface is that the

machining operation occurs on a curved

surface.

Notice that the

depth can not

be specified in

the note.


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h) Countersunk Holes

Drill DIA

Drill Depth

C’Sink DIA

C’Sink angle

Space


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� What do you think a countersunk hole is

used for?


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i) Chamfers: Dimensioned by a linear

dimension and an angle, or by two linear

dimensions.


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i) Chamfers: Dimensioned by a linear

dimension and an angle, or by two linear

dimensions.

Space


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� What do you think a chamfer is used for?

Safety.

Improve engagement of mating parts.


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Drawing Notes

� Drawing notes give additional

information that is used to complement

conventional dimension.

→ manufacturing requirements

→ treatments and finishes

→ blanket dimensions (e.g. size of all rounds

and fillets on a casting or a blanket

tolerance).

� The note area is identified with the

heading “NOTE:”.


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Exercise 2-8

Advanced features


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Exercise 2-8

� List the

dimensioning

mistakes and

then

dimension

the object

correctly.

What are the 7

dimensioning

mistakes?

1 & 2) Use

symbols

3) Spaces

/ Angle up5) Radius

7) Locate radius center

6) Don’t

dim.

hidden

features

4) Dim. where

features is

shown best

Correctly

Dimensioned


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Dimensioning

2-6) Dimension Choice


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Dimension Choice

� Dimension placement and dimension

text influences the manufacturing

process used to make the part.

→ Manufacturing process should not be

specifically stated on the drawing.

� Choose dimensions based on function

first then manufacturing.


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Units and Decimal Places

a) Decimal dimensions should be used for

all machining dimensions.

→ You may encounter a drawing that specifies

standard drills, broaches, and the like by

size.

→ For drill sizes that are given by number or

letter, a decimal size should also be given.


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b) Metric dimensions are given in ‘mm’ and

to 0 or 1 decimal place (e.g. 10, 10.2).

→ When the dimension is less than a

millimeter, a zero should proceed the

decimal point (e.g. 0.5).


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c) English dimensions are given in ‘inches’

and to 2 decimal places (e.g. 1.25).

→ A zero is not shown before the decimal

point for values less than one inch (e.g.

.75).


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d) Metric 3rd angle drawings are designated

by the SI symbol.


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Locating Features Using Datums

� Consider three mutually perpendicular

datum planes.

→ These planes are imaginary and

theoretically exact.


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� Now, consider a part that touches all

three datum planes.

→ The surfaces of the part that touch the

datum planes are called datum features.


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� Most of the time, features on a part are

located with respect to a datum feature.


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� How do we choose which surface will

be a datum feature?

� Good datum features are:

→ functionally important surfaces

→ mating surfaces

→ big enough to permit its use in

manufacturing the part


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� In a class setting, do we always know

the function of the part?

� We need to make an educated guess as

to the function of the part.


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a) Datum dimensioning is preferred over

continuous dimensioning.


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b) Dimensions should be given between

points or surfaces that have a functional

relation to each other

→ Slots, mating hole patterns, etc...


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� Why is the distance between the two

holes functionally important?

If the hole pattern

mates with 2 pins or

bolts, the distance

between the holes is

more important than

the distance from

the edge to the

second hole.


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Dimension Accuracy

� There is no such thing as an "exact"

measurement.

→ Every dimension has an implied or stated

tolerance associated with it.

→ A tolerance is the amount a dimension is

allowed to vary.


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Exercise 2-9

Dimension Accuracy


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Exercise 2-9

� Which dimensions have implied

tolerances and which have stated

tolerances?

Implied StatedImplied


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Exercise 2-9

� Does the arrow indicate an increasing

or decreasing accuracy?

Increasing


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Exercise 2-9

� Write down the range in which the

dimension values are allowed to vary.

> 0.5

< 1.5

> 0.95

< 1.05

0.999

1.001


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Rounding Off

� The more accurate the dimension the

more expensive it is to manufacture.

→ To cut costs it is necessary to round off

fractional dimensions.


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Rounding Off

� How do we round off?

→ Let’s round off to the second decimal place.

1.125

2nd decimal place 3rd decimal place


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Rounding Off

� If the third decimal place number is:

→ less than 5, we truncate after the second

decimal place.

1.123 1.12


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Rounding Off


→ greater than 5, we round up and increase

the second decimal place number by 1.

1.126 1.13


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Rounding Off


→ exactly 5, whether or not we round up

depends on if the second decimal place

number is odd or even. If it is odd, we

round up and if it is even, it is kept the

same.

1.165 1.16

1.135 1.14


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Exercise 2-10

Rounding Off


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Exercise 2-10

� Round off the following fractions to

two decimal places according to the

rules stated above.

(5/16) .3125 →

(5/32) .1562 →

(1/8) .125 →

(3/8) .375 →

.31

.16

.12

.38


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Cumulative Tolerances

� Continuous dimensioning has the

disadvantage of accumulating error.

→ It is preferable to use datum dimensioning to

reduce error buildup.


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Cumulative Tolerances

� What is error build up?

→ e = individual dimension error

x.e 3x.e

x.e + x.e + x.e = 3x.3e


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Exercise 2-11

Dimension Choice


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Exercise 2-11



1 & 2) 2 decimal places / No leading zero

4) Symbol / Decimal

3) Use datum dimensioning

5) Don’t dim. hidden features


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Exercise 2-12

Dimensioning 1


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Exercise 2-12

� Dimension

the following

object using

proper

dimensioning

techniques.

Did we need the

right side view?

Notice the

datum features

that were used.


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Exercise 2-13

Dimensioning 2


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Exercise 2-13

� Dimension the following object using

proper dimensioning techniques.


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Exercise 2-14

Dimensioning 3


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Exercise 2-14

� Dimension the following object using

proper dimensioning techniques.


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Exercise 2-15

Dimensioning 4


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Exercise 2-15

� Dimension

the following

object using

proper

dimensioning

techniques.


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Dimensioning

The End

chapter 2: dimensioning -...

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