262
Exploring Drafting
only minutes or seconds are specifi ed in an
angular dimension, 0° should precede the
number of minutes or seconds.
Angles are dimensioned as shown in
Figure 10-29. The origin (vertex) of the angle
must be located and the size given. Whenever
possible, locate the vertex with respect to an
original edge of the original mass, not with
respect to another feature. See Figure 10-30.
Dimensioning Small
Portions of an Object
There are many cases where the size of
object features limits the space available to
place dimensions. When the space between
extension lines is too small for both the
numbers of the dimension and the arrowheads,
dimensions are placed as shown in Figure 10-31.
These are just several alternatives. There are
other options that are also acceptable. See
your instructor for recommendations.
the edges of the round feature, Figure 10-27.
However, as previously discussed, it is best to
locate the center points of round features with
respect to the original edges of the original
mass of the object.
When it is necessary to dimension a series
of holes that lie in a radial (circular) pattern,
a special note (grouping statement) is created
to designate the number of holes, their size,
and the diameter of the circle on which they
are located. See Figure 10-28. If the holes are
equally spaced in the circular pattern, the
information should be included in the grouping
statement. Refer to Figure 10-28A.
Dimensioning Angles
Angular dimensions are expressed either
in degrees and decimal parts of a degree or in
degrees (°), minutes (′), and seconds (″). Where
degrees are indicated alone, the numerical
value is followed by the degree symbol. Where
_
4
R1
_
4
R1
R1
R.75
R.25
A B C
Goodheart-Willcox Publisher
Figure 10-26. Recommended methods for dimensioning arcs.
5.0
.75
.37
∅1.0
∅1.5
∅1.24
∅.75
Goodheart-Willcox Publisher
Figure 10-27. Round holes and cylindrical parts are dimensioned from the centers when placing location dimensions.
Copyright Goodheart-Willcox Co., Inc.