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GENERAL KNURLING INFORMATION
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Knurling is widely used in industry
for many applications. Some of these include: decorative and
"grip" surfaces, repair of undersized shafts and oversize
bores, and driving serrations and splines. The word
"knurling" applies to both the method of production, and the
rolled section on the part. It is usually produced by
forcing a knurling die into the surface of a rotating part,
displacing material from the original diameter. Two methods
of specifying the comparative tooth spacing are currently in
use - CIRCULAR PITCH and DIAMETRAL PITCH. The CIRCULAR PITCH
system has been used for many years and is based on the
distance between teeth (pitch) and expressed as TEETH per
INCH of circumference or TPI. The DIAMETRAL PITCH system is
fully explained in American Standard ANSI/ASME B94.6-1984.
Unlike gearing, only four standard pitches are used (64, 96,
128, & 160) for blank diameters from 3/32" to 1". Diametral
Pitch dies are designed to permit accurate tracking on
standard fractional sized blanks, making blank diameter
selection easier. Due to the many variables involved in any
knurling operation (speeds, feeds, coolant, hardness of
piece, condition of pins, etc.), determining proper blank
diameters for circular pitch dies is a bit more difficult,
and usually involves some amount of experimentation. The
tips along with the formulas on the following pages should
help, but if problems persist, just give us a call and we'll
be glad to offer our advise.
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SPEEDS
AND FEEDS
Knurling is normally done at the same speed as cutting
operations. Bump knurling from the cross-slide should
be done in 10 to 20 revolutions. (Over rolling will
cause flaking and poor knurl life). Knurls from the
turret should be fed onto the work
at about .005 to .020 per rev. (slower for harder
materials faster for soft materials) and off the work
about twice as fast. For turret knurling, a faster,
feed rate may correct a tracking problem, as this would
make a larger impression on the first revolution, thus
increasing the chance of the teeth falling in place on
the second revolution even though the spacing were off
slightly.
Note: bevels are recommended when traverse
knurling.
Bevels will be provided at no extra charge when
requested, but beveled knurls may not be returned if
ordered in error.
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TRACKING (AND MIS-TRACKING)
When a single knurl makes its first revolution and then
falls back into the first tooth that it rolled, it is
tracking correctly. If the circumference of the part
being rolled is not an approximate multiple of the pitch
of the knurl, the knurl may land somewhere between the
two initial teeth, causing it to start a
new row. This may cause double tracking (or any
multiple of the initial pitch). This problem can
usually be corrected by changing the diameter of the
work by +/- .005" to .010". Otherwise, order a
special knurl.
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