LATHE OPERATIONS - OD1645 - LESSON 1/TASK 1
(b) Rough Cuts. For rough cuts, the feed may be relatively heavy since
the surface need not be exceptionally smooth. For most materials, the feed
for rough cuts should be 0.010 to 0.020 inch per revolution. The feed may
be 0.040 inch on large lathes with larger diameter workpieces. Care must be
taken when turning slender workpieces as a heavy cut may bend the piece,
ruining it. In this case, it is best to reduce the feed to 0.008 - 0.015
inch per revolution.
(c) Finish Cuts.
For finish cuts, a light feed is necessary since a
heavy feed causes a built-up edge to form on the surface, which produces a
poor finish. If a large amount of stock is to be removed, it is advisable
to take one or more roughing cuts and then take light finishing cuts at
relatively high speeds.
For most materials, the feed for finishing cuts
should be 0.003 to 0.010 inch per revolution.
An exception is finishing
soft metal like aluminum where a broad nose cutter bit is used at feeds as
great as 1/8 to 1/2 inch per revolution.
(4) Depth of Cut.
(a) General. The depth of cut regulates the reduction in the diameter
of the workpiece for each longitudinal traverse of the cutter bit.
The
workpiece diameter is reduced by twice the depth of the cut in each complete
traverse of the cutter bit. Generally, the deeper the cut, the slower the
speed, since a deep cut requires more power.
(b) Rough Cuts. The depth of the cut for roughing is generally five to
ten times deeper than the feed.
The reason for this is that more of the
cutting edge of the cutter bit is in contact with the workpiece for the
amount of metal being removed permitting a greater speed to he used. For
roughing with feeds of from 0.010 to 0.020 inch per revolution, the depth of
cut should be between 3/16 and 1/4 inch. Deeper cuts up to 1/2 inch can be
taken but the feed should be proportionately reduced. A heavy cut may cause
the workpiece and the cutter bit to chatter; in this case the depth of cut
should be reduced.
(c) Finish Cuts. Finish cuts are generally very light; therefore, the
cutting speed can be increased since the chip is thin.
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