Dimensioning and Notation
Chapter 6
Sacramento City College
EDT 300/ENGR 306
EDT 300/ENGR 306 - Chapter 6
1
Objectives
‹ Apply
measurements, notes and symbols to
orthographic views on a technical drawing
‹ Use ANSI standards for dimensioning and
notes
‹ Differentiate between size dimensions and
location dimensions.
‹ Dimension a technical drawing using either
the SI or US units
‹ Determine appropriate sizes for precision fits
between matching parts
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‹EDT
300/ENGR 306 - Chapter 6
Objectives
‹ Specify
geometric tolerances using symbols
and notes
‹ Designate appropriate surface textures
3
‹EDT
300/ENGR 306 - Chapter 6
Vocabulary
Aligned system
‹ Assembly drawing
‹ Basic hole systems
‹ Basic shaft systems
‹ Bilateral tolerances
‹ Datums
‹ Detail Drawing
‹ Dimension line
‹ Dimensioning
‹ Dual-dimensioning
system
‹
4
‹EDT
Extension lines
‹ Finish mark
‹ Geometric
dimensioning and
tolerancing
‹ Leader
‹ Outline view
‹ Tolerance
‹ Unidirectional system
‹ Unilateral tolerances
‹
300/ENGR 306 - Chapter 6
Goal of Chapter
‹ This
chapter discusses how to show the size
of the objects you draw.
‹ Dimensioning
‹ Showing
5
is
an object’s size
‹EDT
300/ENGR 306 - Chapter 6
Dimensioning
‹ Dimensioning
- is the process whereby
‹ size
and
‹ location data
‹ Are
shown for a technical drawing.
‹ Notation
- is the process whereby needed
information not covered by dimensions is
placed on technical drawings.
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‹EDT
300/ENGR 306 - Chapter 6
Dimensioning
‹ ANSI
Y14.5M is the most widely accepted
dimensioning standard.
‹ This
standard applies in most instances where
interchangeability of parts is a major
consideration.
‹ Automobile parts - good example.
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‹EDT
300/ENGR 306 - Chapter 6
Dimensions
‹ Three
US.
‹ 1.
dimensioning formats are used in the
Decimal-inch dimensioning.
‹ Example:
‹ 2.
Fractional inches.
‹ Example:
‹ 3.
1-3/8”
Metric SI units.
‹ Example:
8
1.375”
1.375 mm
‹EDT
300/ENGR 306 - Chapter 6
Dimensions
‹ In
in:
the US system, measurements are given
‹ 1.
Feet and Inches.
‹ 40’-
‹ 2.
6 1/2”
Inches and Fractions.
‹ 6-1/2”
‹ 3.
Decimal Divisions of Inches.
‹ 6.5”
‹ Most
9
commonly used.
‹EDT
300/ENGR 306 - Chapter 6
Dimensions
‹ Decimal
divisions are
‹ Most
commonly used throughout industry.
‹ Used exclusively in ANSI Y14.5 M (the
drafting standard on dimensioning).
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‹EDT
300/ENGR 306 - Chapter 6
Dimensioning Systems
‹ Metric
units are often used for engineering
drawings.
‹ Civil
engineering drawings may be
dimensioned in meters.
‹ Architectural
drawings may use both meters
and millimeters.
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‹EDT
300/ENGR 306 - Chapter 6
Lines and Symbols for Dimensioning
‹ Dimensioning
is standardized.
‹ Professional
and trade associations.
‹ Engineering societies.
‹ Certain industries.
‹ have
agreed upon the symbols so people who
use the drawings can recognize their
meaning.
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‹EDT
300/ENGR 306 - Chapter 6
Lines and Symbols for Dimensioning
‹ Organizations
standards:
that publish dimensioning
‹ 1.
The American National Standards Institute
(ANSI).
‹ 2. The Society of Automotive Engineers.
(SAE)
‹ Automotive.
‹ 3.
The Military Standards. (MIL-Specs)
‹ Military.
‹ 4.
The International Standards Organization
(ISO).
‹ Parts
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for international market.
‹EDT
300/ENGR 306 - Chapter 6
Orienting Dimensions
‹ Dimension
Formats:
‹ The
aligned system.
‹ The unidirectional system.
‹ Refer
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to page 167, 168.
‹EDT
300/ENGR 306 - Chapter 6
Orienting Dimensions
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‹EDT
300/ENGR 306 - Chapter 6
Placing Dimensions
‹ The
aligned system
‹ Dimensions
are place in line with the
dimension lines.
‹ Once was the only system in use.
‹ See Figure 6-13.
‹ Avoid
placing dimensions in the shaded areas
shown in Figure 6-14.
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‹EDT
300/ENGR 306 - Chapter 6
Placing Dimensions
‹ The
Unidirectional System
‹ All
dimensions read from the bottom of the
sheet no matter where they appear.
‹ Think “horizontal text”.
‹ See Figure 6-15.
‹ The Unidirectional System, has replaced the
Aligned System in most industries.
‹ ANSI Y14.5M uses the unidirectional system
exclusively.
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‹EDT
300/ENGR 306 - Chapter 6
Placing Dimensions
‹ Notes
and dimensions with leaders ALWAYS
read from the bottom of the drawing.
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‹EDT
300/ENGR 306 - Chapter 6
Dimensioning
‹ Notes
and symbols
‹ Show
‹ Finish
‹ Materials,
and
‹ other information needed to make a part
‹ Are
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components of dimensioning.
‹EDT
300/ENGR 306 - Chapter 6
Working Drawing
‹A
working drawing is used to build the part or
building.
‹ includes
‹ Shape
description,
‹ Measurements
‹ Notes and
‹ Symbols.
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‹EDT
300/ENGR 306 - Chapter 6
Working Drawing
‹ Dimension precision
‹ Show only as precise
as necessary to allow
the manufacturer to create the part.
‹ Example: Framing dimensions
‹ 40’-5.000330
inches
‹ Is meaningless.
‹ TOO MUCH precision is shown.
‹ Example:
Auto engine parts
‹ Piston
– diameter 5.2
‹ Cylinder – diameter 5.21
‹ Not ENOUGH precision is shown.
‹ Is meaningless.
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‹EDT
300/ENGR 306 - Chapter 6
Working Drawing
‹ Dimensions
are given in
‹ Feet
‹ Ones
‹ Tenths
‹ Hundredths
‹ Thousandths
‹ Ten-thousandths
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‹EDT
of an inch.
300/ENGR 306 - Chapter 6
Complete Working Drawing
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‹EDT
300/ENGR 306 - Chapter 6
Lines and Symbols for Dimensioning
‹ Lines
and symbols show where the
dimensions apply.
‹ Measurements
are shown on the drawings.
‹ The drawing is NOT scaled or measured !
‹ Cannot
measure a drawing accurately enough
for many interchangeable parts that must fit
closely together.
‹ How
would you measure 5.03456” on a
drawing?
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‹EDT
300/ENGR 306 - Chapter 6
Lines and Symbols for Dimensioning
‹ Add
size information to the drawing using a
system of
‹ Lines
‹ Symbols
‹ Numerical
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values.
‹EDT
300/ENGR 306 - Chapter 6
Lines and Symbols for Dimensioning
‹ Lines
and symbols are used on drawings to
show where the dimensions apply.
‹ See
26
Figure 6-2.
‹EDT
300/ENGR 306 - Chapter 6
Figure 6-2
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‹EDT
300/ENGR 306 - Chapter 6
Dimension Components
EDT 300/ENGR 306 - Chapter 6
28
Dimension Components
‹ 1.
Dimension Lines
‹ Is
a thin line
‹ Shows where a measurement begins and
where it ends.
‹ Show the size of an angle.
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‹EDT
300/ENGR 306 - Chapter 6
Dimension Components
‹ 1.
Dimension Lines
‹ Show
a break in it for dimension numbers.
‹ Be drawn about 0.38” from the drawing to
allow for the dimension number.
‹ Be drawn about 0.25” from other dimensions.
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‹EDT
300/ENGR 306 - Chapter 6
Dimension Components
‹ 1.
Dimension Lines
‹ Mechanical
Style
‹ Start
and end with arrowheads.
‹ Continuous line with gap in center
‹ Dimension value is centered in the gap.
‹ Architectural
Style
‹ Start
and end with “tic” marks.
‹ Continuous line with NO gap in center.
‹ Dimension value is centered over the
dimension line.
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‹EDT
300/ENGR 306 - Chapter 6
Dimension Components
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‹EDT
300/ENGR 306 - Chapter 6
Dimension Components
‹ 2.
Arrowheads and Tic Marks
‹ Are
placed at the ends of dimension lines.
‹ Show where a dimension begins and ends.
‹ Are used at the end of a leader to show where
a note or dimension applies.
‹ Can be open or solid.
‹ Should be one size and shape in any one
drawing.
‹ See Figure 6-4.
‹ Mechanical
– arrowheads
‹ Architectural - tics
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‹EDT
300/ENGR 306 - Chapter 6
Dimension Components
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‹EDT
300/ENGR 306 - Chapter 6
Dimension Components
‹ 3.
Extension Lines
‹ Are
thin lines
‹ Extend the lines or edges of the views or part.
‹ Are used to locate center points.
‹ Are used to provide space for dimension lines
(Figure 6-5).
‹ Are not part of the views and should not touch
the outline.
‹ Start about 0.06” from the part.
‹ Extend to about 0.12” beyond the last
dimension line.
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‹EDT
300/ENGR 306 - Chapter 6
Dimension Components
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‹EDT
300/ENGR 306 - Chapter 6
Dimension Components
‹ 4.
Numerals and Notes
‹ CAPITAL
LETTERS ARE PREFERRED.
‹ Vertical or Inclined letters.
‹ About 0.125” high.
‹ Must be easy to read.
‹ Draw light guidelines first.
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‹EDT
300/ENGR 306 - Chapter 6
Dimension Components
‹ 5.
Leaders
‹A
thin line
‹ Drawn from the note or dimension to the place
where it applies.
‹ Drawn at an angle to the horizontal.
‹ 60o
is preferred but 45o, 30o or other angles can
be used.
‹ Start
with an 1/8” long dash
‹ End with an arrowhead.
‹ Use a dot if the leader is pointing to a surface
rather than to an edge (Fig 6-8).
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‹EDT
300/ENGR 306 - Chapter 6
Leaders
‹ 5.
Leaders
‹ Many
leaders drawn close together
‹ Draw them parallel to each other.
‹ Draw a leader to a circle or arc so that the
arrowhead points to its center.
‹ Use one leader per dimension, (don’t try to
economize).
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‹EDT
300/ENGR 306 - Chapter 6
Leaders
‹ 5.
Leaders
‹ Leader
“Don’ts”
‹ Do
not draw long leaders.
‹ Do not draw horizontally, vertically, or at a
small angle.
‹ Do not draw leaders parallel to dimensions,
extensions or section lines.
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‹EDT
300/ENGR 306 - Chapter 6
The Finish Mark
EDT 300/ENGR 306 - Chapter 6
41
The Finish Mark
‹ The
finish mark or surface-texture symbol
shows that a surface is to be machined
‹ See
Figure 6-7.
‹ The older symbol is still used but it is being
replaced.
‹ The standard symbol now in general use is
shown in Figure 6-7.
‹ The point of the symbol should touch the edge
view of the surface.
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‹EDT
300/ENGR 306 - Chapter 6
Scale of A Drawing
EDT 300/ENGR 306 - Chapter 6
43
Scale of A Drawing
‹ The
title.
scale should be given near the drawing
‹ If
the drawing has views of more than one
part, and different scales are used,
‹ Show
44
the scale close to the views.
‹EDT
300/ENGR 306 - Chapter 6
Units and Parts of Units
‹ If
parts require a great deal of accuracy use
decimal dimensioning.
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‹EDT
300/ENGR 306 - Chapter 6
Units and Parts of Units
‹ Decimal
between
dimensioning is commonly used
‹ finished
surfaces.
‹ center distances.
‹ pieces that must be held in a definite, accurate
relationship to each other.
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‹EDT
300/ENGR 306 - Chapter 6
Units and Parts of Units
‹ With
customary measures, decimals are
shown to two places where limits of +/- 0.01”
are close enough.
‹ Use
decimals to three places where where
limits smaller than +/- 0.01” are required.
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‹EDT
300/ENGR 306 - Chapter 6
Units and Parts of Units
‹ Decimal
dimensioning is used in most
industries.
‹A
dual dimensioning system is sometimes
used in industries involved in international
trade.
‹ This
system uses both the decimal inch and
the millimeter.
‹ It is becoming more common to use the metric
system alone.
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‹EDT
300/ENGR 306 - Chapter 6
Theory of Dimensioning
‹ Two
kinds of dimensions exist
‹ Size
dimensions
‹ Location dimensions
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‹EDT
300/ENGR 306 - Chapter 6
Theory of Dimensioning
‹ Size
dimensions
‹ Define
the size of each piece.
‹ Show the dimensions of a number of simple
shapes
‹ Basic
geometric forms
‹ Prisms
‹ Cylinders
‹ Pyramids
‹ Cones, etc.)
‹ See
50
Figure 6-16.
‹EDT
300/ENGR 306 - Chapter 6
Theory of Dimensioning
‹ Location
‹ Show
dimensions
the positions of each piece must also be
given.
‹ Each piece is considered separately and then
in relation to the other pieces.
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‹EDT
300/ENGR 306 - Chapter 6
Size Dimensions - Prisms
EDT 300/ENGR 306 - Chapter 6
52
Size Dimensions - Prisms
‹ The
Prism is the first basic shape we will
consider
‹ For a rectangular prism, the width, height,
and depth are needed.
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‹EDT
300/ENGR 306 - Chapter 6
Size Dimensions - Prisms
‹ For
any flat piece, give
‹ The
thickness in the edge view.
‹ All other dimensions in the outline view.
‹ The Outline View is the one that shows the
shape of the flat surface or surfaces.
‹ The front views in Fig 6-19 are outline views.
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‹EDT
300/ENGR 306 - Chapter 6
Size Dimensions - Prisms
‹ Methods
for dimensioning other prisms are
shown in Figure 6-20.
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‹EDT
300/ENGR 306 - Chapter 6
Size Dimensions - Prisms
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‹EDT
300/ENGR 306 - Chapter 6
Size Dimensions – Prisms
EDT 300/ENGR 306 - Chapter 6
57
Size Dimensions - Cylinders
‹ The
cylinder requires two dimensions
‹ the
diameter.
‹ the length.
‹ For
cylindrical pieces, give the diameter and
the length on the same view.
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‹EDT
300/ENGR 306 - Chapter 6
Size Dimensions - Cylinders
‹ The
symbol Ø is always placed with the
diameter.
‹ Example: Ø 1.625”
‹ The
abbreviation DIA may be found on older
drawings instead of the symbol Ø.
‹ Notes are used to give hole sizes, and are
placed in the outline view.
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‹EDT
300/ENGR 306 - Chapter 6
Size Dimensions - Cylinders
‹ When
parts of cylinders occur, such as fillets
and rounds they are dimensioned in the view
in which the curves show.
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‹EDT
300/ENGR 306 - Chapter 6
Size Dimensions - Cylinders
‹ The
other shapes:
‹ Cone
‹ Frustum
‹ Square
pyramid
‹ Sphere
‹ can
61
be dimensioned in one view.
‹EDT
300/ENGR 306 - Chapter 6
Location Dimensions
EDT 300/ENGR 306 - Chapter 6
62
Location Dimensions
‹ Location
dimensions
‹ Show
the relative positions of the basic
shapes.
‹ Locate holes, surfaces and other features.
‹ Location
dimensions are needed in three
mutually perpendicular directions.
‹ Up
/ down.
‹ Crossways.
‹ Forward and backward.
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‹EDT
300/ENGR 306 - Chapter 6
Steps In Dimensioning
‹ Two
basic steps
1. Apply the size dimension
‹ This
gives the overall size of the object and
the various features which make up the object.
2. Apply the location dimension
‹ Location
dimensions are dimensions which
locate various features of an object from some
specified datum or surface.
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‹EDT
300/ENGR 306 - Chapter 6
Location Dimensions - Prisms
‹ Prisms
are located by
‹ Surfaces
‹ Surfaces
and axes
‹ Axes
‹ Three
65
dimensions are needed
‹EDT
300/ENGR 306 - Chapter 6
Location Dimensions - Cylinders
‹ Cylinders
are located by
‹ Axes
and bases.
‹ Three dimensions are needed
‹ Refer
66
to Fig 6-30.
‹EDT
300/ENGR 306 - Chapter 6
Datum Dimensioning
EDT 300/ENGR 306 - Chapter 6
67
Datum Dimensioning
‹ Datum
are points, lines and surfaces that are
assumed to be exact
‹ Datum
‹ Location
are used to compute other dimensions.
dimensions are given from datum.
‹ When
positions of a part are given, they are all
located from the same datum.
‹A
68
datum must be clear.
‹EDT
300/ENGR 306 - Chapter 6
Rules for Dimensioning
EDT 300/ENGR 306 - Chapter 6
69
Rules for Dimensioning
1. Space dimension lines about
‹ 0.25”
apart and
‹ 0.38” from the view outline.
2. Aligned system - dimensions
‹ read
in line with the dimension line
‹ Read aligned with part.
‹ Refer to Fig 6-12.
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‹EDT
300/ENGR 306 - Chapter 6
Rules for Dimensioning
3. Unidirectional system - dimensions
‹ read
in line with the dimension line
‹ Read left to right from bottom of sheet.
‹ Refer to Fig 6-14.
4. Machine drawings
‹ Use
71
decimal inches or millimeters.
‹EDT
300/ENGR 306 - Chapter 6
Rules for Dimensioning
5. When all dimensions are in inches or
millimeters, omit the symbol.
‹ Add
a note:
‹ “ALL DIMENSIONS ARE IN INCHES”.
6. Position all dimensions clearly.
7. Do not repeat the same dimension on
different views.
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‹EDT
300/ENGR 306 - Chapter 6
Rules for Dimensioning
8. Do not give dimensions that are not needed.
9. Place overall dimensions outside the smaller
dimensions
‹ See
Figure 6-31.
‹ See Figure 6-32.
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‹EDT
300/ENGR 306 - Chapter 6
Rules for Dimensioning
10. Avoid placing dimensions in the shaded
areas when using the aligned system (Fig 635).
11. Give dimensions from centerlines, finished
surfaces or datums where needed.
12. Do not use a centerline or line of a view as
a dimension line.
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‹EDT
300/ENGR 306 - Chapter 6
Rules for Dimensioning
13. Do not draw a dimension line that extends
from a line of a view.
14. Avoid crossing a dimension line with
another line.
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‹EDT
300/ENGR 306 - Chapter 6
Rules for Dimensioning
15. Give the diameter of a circle, not the radius.
Use the symbol Ø before the dimension.
16. Place the abbreviation “R” before the
dimension when giving the radius of an arc.
17. In general, dimensions should be placed
outside the view outlines.
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‹EDT
300/ENGR 306 - Chapter 6
Rules for Dimensioning
18. Do not draw extension lines that cross each
other or cross dimension lines if possible.
19. Avoid dimensioning to a hidden line if
possible.
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‹EDT
300/ENGR 306 - Chapter 6
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‹EDT
300/ENGR 306 - Chapter 6
Dimensioning a Detail Drawing
EDT 300/ENGR 306 - Chapter 6
79
Dimensioning a Detail Drawing
‹A
detail drawing is a drawing for a single part
that includes all the information necessary to
make that part.
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‹EDT
300/ENGR 306 - Chapter 6
Dimensioning a Detail Drawing
‹ Dimension
order:
a detail drawing in the following
1.Complete all views first before adding any
dimensions or notes
2. Think about the part first, and its
characteristic views
3. Think about the size dimensions and the
related location dimensions. Draw the
dimension lines, leaders and arrowheads
4. After considering any changes, add any
dimensions and notes that may be needed.
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‹EDT
300/ENGR 306 - Chapter 6
Dimensioning an Assembly Drawing
EDT 300/ENGR 306 - Chapter 6
82
Dimensioning an Assembly Drawing
‹ An
assembly drawing shows parts of a
machine in their relative positions.
‹ If
an assembly drawing needs a complete
description of size, the rules and methods of
dimensioning apply.
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‹EDT
300/ENGR 306 - Chapter 6
Dimensioning an Assembly Drawing
‹ 1.
If the drawing is to show arrangement of
parts or appearance only, leave dimensions
off.
‹ 2.
If a drawing is needed to show the space a
product requires, give overall dimensions.
‹ 3.
If parts can be located in relation to each
other without giving detail dimensions,
center-to-center dimensions are usually
given.
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‹EDT
300/ENGR 306 - Chapter 6
Abbreviations
‹ Examples
of abbreviations from ANSI are
listed in Appendix C of the text.
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‹EDT
300/ENGR 306 - Chapter 6
Limit Dimensioning
EDT 300/ENGR 306 - Chapter 6
86
Limit Dimensioning
‹ Parts
are generally manufactured with a
tolerance.
‹ A tolerance is an allowable variation in the
part dimension
‹ The
tolerance may be stated in a note
“DIMENSION TOLERANCE +/- 0.01 UNLESS
OTHERWISE SPECIFIED”
‹ Limit
dimensions give the max and min
dimensions allowed
‹ The
max limit is placed over the min limit
‹ Fig 6-47B and C
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‹EDT
300/ENGR 306 - Chapter 6
Limit Dimensioning
‹ Consecutive
dimensions are listed one after
the other
‹ Progressive dimensions are all given from a
single surface (Figure 6-47 C). This is called
baseline dimensioning
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‹EDT
300/ENGR 306 - Chapter 6
Expressing Size
‹ Size
is a designation of magnitude.
‹ When a value is given to a dimension it is
called the size of that dimension
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‹EDT
300/ENGR 306 - Chapter 6
Expressing Size
‹ Nominal
size - used for general identification.
‹ Basic size - is the size to which allowances
and tolerances are added to get the limits of
size.
‹ Design size - the size to which tolerances are
added to get the to get the limits of size.
‹ Actual size - is the measured size.
‹ Limits of size - is the max and min sizes.
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‹EDT
300/ENGR 306 - Chapter 6
Expressing Position
‹ Locating
round holes
‹ x-y
coordinates
‹ polar coordinates
‹ “equally spaced” holes
‹ Datum line dimensions
‹ Point-to-point or chain dimensioning
‹ Datum dimensioning
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‹EDT
300/ENGR 306 - Chapter 6
Tolerance
‹A
tolerance is the total amount a given
dimensions may vary.
‹ Express
in the same form as its dimension.
‹ Express in the same number of decimal
places.
‹ If
the dimension is written as fraction, the
tolerance should be also written as a common
fraction.
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‹EDT
300/ENGR 306 - Chapter 6
Tolerance
‹ In
a chain of dimensions with tolerances, the
last dimension may have a tolerance equal to
the sum of the tolerances between it and the
first dimension.
‹ Tolerances
together).
93
accumulate (they are added
‹EDT
300/ENGR 306 - Chapter 6
Tolerance
‹ In
a datum dimensioning, tolerances do NOT
add together.
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‹EDT
300/ENGR 306 - Chapter 6
Tolerances
‹ Unilateral
tolerances
‹ Allow
variations in only one direction from a
design size.
‹ Bilateral
tolerances
‹ Allow
variations in both directions from a
design size.
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‹EDT
300/ENGR 306 - Chapter 6
Tolerances
‹ The
Limit System
‹ Only
the largest and smallest allowed
dimensions are shown .
‹ The tolerance is the difference between the
limits.
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‹EDT
300/ENGR 306 - Chapter 6