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C H A P T E R T E N
DIMENSIONING
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2Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
OBJECTIVES
1. Use conventional dimensioning techniques to describe size andshape accurately on an engineering drawing.
2. Create and read a drawing at a specified scale.
3. Correctly place dimension lines, extension lines, angles, and notes.
4. Dimension circles, arcs, and inclined surfaces.
5. Apply finish symbols and notes to a drawing.
6. Dimension contours.
7. Use standard practices for dimensioning prisms, cylinders, holes,
and curves.
8. List practices for dimensioning a solid model as documentation.
9. Identify guidelines for the dos and donts of dimensioning.
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3Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
UNDERSTANDING DIMENSIONING
The increasing need for precision manufacturing and interchangeability
has shifted responsibility for size control to the design engineer or detail drafter.
Practices for dimensioning architectural
and structural drawings are similar
in many ways to those for dimensioningmanufactured parts, but some practices
differ.
Refer to the following standards:
ANSI/ASME Y14.5-2009 Dimensioning and Tolerancing
ASME Y14.41-2003 Digital Product definition Data Practices
ASME B4.2-1978 (R1999) Preferred Metric Limits and FitsAutomatically Generated Dimensions.
Views and dimensions can be generated
automatically from a solid model.
(Courtesy of Robert Kincaid.)
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4Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
Three Aspects of Good Dimensioning
Technique of dimensioning
Placement of dimensions
Choice of dimensions
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5Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
ToleranceTolerance is the total amount that the feature on the actual part is allowed
to vary from what is specified by the drawing or model dimension.
A Title Block Specifying Tolerances. (Courtesy of Dynojet Research, Inc.)
ALL TOLERANCES .02 INCH
UNLESS OTHERWISE NOTED.EX
AMPLES
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6Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
Geometric Breakdown
Engineering structures are composed
largely of simple geometric shapes, suchas the prism, cylinder, pyramid, cone,
and sphere. They may be exterior
(positive) or interior (negative) forms.
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8/438Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
Guidelines for
USING DIMENSION
AND EXTENSION LINES
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9/439Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
ARROWHEADS
When you are drawing by hand and using
the arrowhead method in which bothstrokes are directed toward the point, it is
easier to make the strokes toward yourself.
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10/4310Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
LEADERSA leader is a thin, solid line directing attention to a note or dimension and
starting with an arrowhead or dot.
For the Best Appearance, Make Leaders
near each other and parallel
across as few lines as possible
Dont Make Leaders
parallel to nearby lines of the drawing through a corner of the view
across each other
longer than needed
horizontal or vertical
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11/4311Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
DRAWING SCALE
AND DIMENSIONING
Many standard title blocks include a
note such as:
DO NOT SCALE DRAWINGFOR DIMENSIONS
Drawing scale is noted in the title block. The drawing should not be scaled for
dimensions. (Courtesy of Dynojet Research, Inc.)
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13/4313Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
DIMENSION UNITSA note stating ALL MEASUREMENTS IN MILLIMETERS or ALL MEASUREMENTS IN
INCHES UNLESS OTHERWISE NOTED is used in the title block to indicate the
measurement units
(Courtesy of Dynojet Research, Inc.)
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14/4314Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
MILLIMETER VALUES
The millimeter is the commonly
used unit for most metric
engineering drawings. One-place millimeter decimals are
used when tolerance limits
permit. Two (or more)place
millimeter decimals are used
when higher tolerances are
required.
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15/4315Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
DECIMAL-INCH VALUESTwo-place inch decimals are typical when tolerance limits permit. Three or more decimal
places are used for tolerance limits in the thousandths of an inch. In two-place decimals,
the second place preferably should be an even digit.
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Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
RULES FOR DIMENSION VALUESGood hand-lettering is important for dimension values on sketches. The shop
produces according to the directions on the drawing so to save time and prevent
costly mistakes, make all lettering perfectly legible.
Make all decimal points bold, allowing ample space. When the metric dimension is
a whole number, do not show either a decimal point or a zero. When the metric
dimension is less than 1 mm, a zero precedes the decimal point.
When the decimal-inch dimension is used on drawings, a zero is not used before the
decimal point of values less than 1 in.
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Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
DUAL DIMENSIONING and
COMBINATION UNITS
Dual dimensioning is used to show metric and decimal-inch dimensions on the samedrawing. Two methods of displaying the dual dimensions are:
1. Position Method2. Bracket Method
DIMENSIONS IN () ARE MILLIMETERS
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Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
DIMENSION SYMBOLSDimensioning symbols are used to replace traditional terms or abbreviations.
Form and Proportion of Dimensioning Symbols.(Reprinted fromASME Y14.5M-1994 (R2004),by permission of The American Society of Mechanical Engineers. All rights reserved.)
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Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
PLACING AND SHOWING
DIMENSIONS LEGIBLYRulesfor the placement of dimensions help you dimension your drawings so
that they are clear and readable
Fitting Dimension Values in Limited Spaces (Metric Dimensions)
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Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
PLACING AND SHOWING
DIMENSIONS LEGIBLY continued
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Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
SUPERFLUOUS DIMENSIONSAll necessary dimensions must be shown, but do not give unnecessary or super f luous
d imens ions.
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22Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
SUPERFLUOUS DIMENSIONS
continued
No unnecessary or super f luous d imens ions.
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23Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
DIMENSIONING ANGLESAngles are dimensioned by specifying the angle in degrees and
a linear dimension.
The coordinate method is
better when a high degree of
accuracy is required
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24Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
DIMENSIONING ARCS, FILLETS AND
ROUNDSA circular arc is dimensioned in the view where its true shape in seen by giving
the value for its radius preceded by the abbreviation R. Individual fillets and
rounds are dimensioned like other arcs.
FILLETS R6 AND ROUNDS R3 UNLESS OTHERWISE SPECIFIED
or
ALL CASTING RADII R6 UNLESS NOTEDor simply
ALL FILLETS AND ROUNDS R6.
SIZE DIMENSIONS CYLINDERS
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25Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
SIZE DIMENSIONS: CYLINDERS
Use to indicate circular shape
Dimensioning a Machine Part Composed of Cylindrical Shapes
Cylinders are usually dimensioned by giving the diameter and length where the
cylinder appears as a rectangle.
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26Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
SIZE DIMENSIONING HOLES
Countersunk, counterbored, spotfaced and tapped holes are usually specified by standard
symbols or abbreviations.
The leader of a note should point to the circular view of the hole, if possible.
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27Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,
Upper Saddle River, NJ 07458. All Rights Reserved.
DIMENSIONING COUNTERBORES AND
SPOTFACES WITH FILLETS
Counterbored hole with afillet radius specified.
When a fillet radius is specified for aspotface dimension, the fillet radius is
added to the outside of the spotface
diameter,
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28Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,Upper Saddle River, NJ 07458. All Rights Reserved.
DIMENSIONING CURVESOne way to dimension
curves is to give a group
of radii.
Both circular and noncircular
curves may be dimensioned by
using coordinate dimensions,or datums.
When angular measurementsare unsatisfactory, you may
give chorda l d imens ions
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29Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,Upper Saddle River, NJ 07458. All Rights Reserved.
DIMENSIONING ROUNDED-END
SHAPES
For accuracy, in parts
dg, overall lengths of
rounded-end shapes
are given, and radii are
indicated, but without
specific values. The
center-to-centerdistance may be
required for accurate
location of some holes.
In part g, the hole
location is more critical
than the location of the
radius, so the two are
located.
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30Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,Upper Saddle River, NJ 07458. All Rights Reserved.
DIMENSIONING
THREADS
Local notes are used to specify dimensions of threads. For tappedholes, the notes should, if possible, be attached to the circular views
of the holes.
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31Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,Upper Saddle River, NJ 07458. All Rights Reserved.
DIMENSIONING TAPERSA taperis a conical surface on a shaft or in a hole. The usual method of dimensioning
a taper is to give the amount of taper in a note, such as TAPER 0.167 ON DIA (with
TO GAGE often added), and then give the diameter at one end with the length or givethe diameter at both ends and omit the length. Taper on diameter means the difference
in diameter per unit of length.
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32Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,Upper Saddle River, NJ 07458. All Rights Reserved.
DIMENSIONING CHAMFERSAchamfer is a beveled or sloping edge. It is dimensioned by
giving the length of the offset and the angle, as in Figure 10.51a.
A 45chamfer also may be dimensioned
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34Technical Drawing with Engineering Graphics, 14/e
Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,Upper Saddle River, NJ 07458. All Rights Reserved.
DIMENSIONING KNURLS
A knur lis a roughened surface to provide a better handgrip or to be used for a press
fit between two parts. For handgrip purposes, it is necessary only to give thepitch of the knurl, the type of knurling, and the length of the knurled area.
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36Technical Drawing with Engineering Graphics, 14/eGiesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,Upper Saddle River, NJ 07458. All Rights Reserved.
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37Technical Drawing with Engineering Graphics, 14/eGiesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,Upper Saddle River, NJ 07458. All Rights Reserved.
SURFACE ROUGHNESSSurface finish is intimately related to the functioning of a surface, and proper
specification of finish of surfaces such as bearings and seals is necessary. Surface
quality specifications should be used only where needed, since the cost of producing
a finished surface becomes greater as the quality of the surface called for is increased.Generally, the ideal surface finish is the roughest that will do the job satisfactorily.
Surface Texture Symbols and
Construction. (Reprinted from
ASME Y14.36M-1996 (R2002), by
permission of The American Society
of Mechanical Engineers. All rights
reserved.)
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38Technical Drawing with Engineering Graphics, 14/eGiesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,Upper Saddle River, NJ 07458. All Rights Reserved.
LOCATION DIMENSIONSAfter you have specified the sizes of the geometric shapes composing the structure, give
locat ion dimensions to s how the relative positions of these geometric shapes.
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41Technical Drawing with Engineering Graphics, 14/eGiesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,Upper Saddle River, NJ 07458. All Rights Reserved.
COORDINATE DIMENSIONING
A set of three mutually perpendicular datum or reference planes is
usually required for coordinate dimensioning. These planes either must
be obvious.
SHEET METAL BENDS
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42Technical Drawing with Engineering Graphics, 14/eGiesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman
2012, 2009, 2003, Pearson Higher Education,Upper Saddle River, NJ 07458. All Rights Reserved.
SHEET METAL BENDS
Bends
In sheet metal dimensioning, allowance must be made for bends. The intersection of
the plane surfaces adjacent to a bend is called the mold line, and this line, rather than
the center of the arc, is used to determine dimensions.
NOTES
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NOTESIt is usually necessary to supplement the direct dimensions with notes. Notes should be brief and
carefully worded to allow only one interpretation. Notes should always be lettered horizontally on the
sheet and arranged systematically. They should not be crowded and should not be placed between
views, if possible. Notes are classified as general notes when they apply to an entire drawing and as
local notes when they apply to specific items.