Unit 11 Machining Specifications and Drawing Notes 207
To eliminate confusion, keyways should not be
dimensioned by a callout, but should be dimensioned
as illustrated in Figure 11-16.
Knurls
Knurls are patterns of ridges and grooves cut
into a cylindrical surface for the purpose of providing
a grip or increasing the diameter of a part. The
pattern is often crisscrossed, leaving a diamond-like
series of ridges. A metal part may feature a knurl so
that it can be force fit into a plastic part. Knurling
standards are covered in ASME B94.6. A knurl
should be specified with respect to pitch, type, and
possibly the diameters before and after the knurl is
made. See Figure 11-17.
Broaching
Broaching is done on a special machine using
a machine cutter called a broach. The broach
progressively “punches” a shape with a series of
cutting teeth. The teeth are set in such a way that
each tooth is a few thousandths of an inch higher
than the preceding one. Broaching can produce holes
of circular, square or irregular outline; keyways;
internal gear teeth; splines; or flat external contours.
Broaching is fast, accurate, and produces a good-
quality finish. As discussed several times in this
unit, the practice of specifying the machine tool to
make a particular feature is discouraged, but if a
broaching operation is specified, it may appear as
shown in Figure 11-18.
.250
.246
1.582
1.578
.250
.246
1.167
1.163
Figure 11-16.
Linear dimensions are used to specify exact distances
for keyways.
Figure 11-17.
A callout for a knurl may specify several items,
including pitch, type, and before and after diameters.
BROACH .125
.375
Figure 11-18.
A callout for a typical broaching operation is shown here.