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Exploring Drafting
If an object is to be manufactured according
to the designer’s specifi cations, the person
making the product usually needs more infor-
mation than that furnished by a scale drawing
of its shape. Dimensions and drawing notes
help provide this information, Figure 10-1.
It is important to realize that the main
purpose for creating, dimensioning, and noting
a drawing is to communicate the size and
shape of the product so that the person making
the product can do so as easily and accurately
as possible. Hence, the most pertinent infor-
mation needed for assembly must be provided.
It is the job of the drafter to defi ne what that
information is and to provide it in the clearest
and most effi cient way.
Dimensions defi ne the size and location of
the features of an object and give the overall
size of the object. Notes provide additional
information not found in the dimensions. In
manual drafting, dimensions and notes are
added to a drawing by hand. In CAD drafting,
drawings are dimensioned using CAD software
commands and tools.
Systems of Measurement
Used in Dimensioning
As discussed in Chapter 4, measurements
on drawings are made in US Customary or
SI Metric units. Dimensions are placed on
drawings using the appropriate units in one
of the two systems of measurement. Sometimes,
drawings are dimensioned using both systems.
In some cases, drawings are completed using
one system for most of the dimensions and
the other system for selected dimensions.
When this occurs, special rules apply. This is
discussed later in this chapter.
When using the US Customary system,
drawings are dimensioned in inches and feet.
The dimensions may be represented in one
of two ways. They may be decimal inch
dimensions (such as 1.5 or 2.75) or fractional
inch dimensions (such as 1-1/2 or 2-3/4).
Decimal dimensioning is the standard practice
recommended by the ASME drafting standard.
In mechanical drafting, drawings based on
the US Customary system are most commonly
Dimensions
Notes
NOTES:
1. REMOVE ALL BURRS
2. BREAK SHARP EDGES .010
MAX
3. DIMENSIONS APPLY AFTER
PLATING
∅.44
.22
.31
.19
60°
.02
45°
.062
1.47
1.13
–18UNC–3
5
16
Goodheart-Willcox Publisher
Figure 10-1. A typical drawing from industry with dimensions and notes.
Copyright Goodheart-Willcox Co., Inc.