MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
reduced and the feed increased.
Too much cutter clearance, a poorly
supported workpiece, or a badly worn machine gear are common causes of
"chattering."
(2)
Typical Feeds.
(a)
Feed for milling cutters will generally run from 0.002 to 0.250 inch
per cutter revolution, depending upon the diameter of the cutter, the kind
of material, the width and depth of the cut, the size of the workpiece, and
the condition of the machine.
(b)
Good finishes may be obtained using a 3-inch plain milling cutter at
a 40 feet per minute speed, with a feed of 0.040-inch per cutter revolution.
(3)
(a)
It is usually regarded as standard practice to feed the workpiece
against the milling cutter (figure 12 on the following page).
When the
piece is fed against the milling cutter, the teeth cut under any scale on
the workpiece surface and any backlash in the feed screw is taken up by the
force of cut.
(b)
As an exception to this recommendation, it is advisable to feed with
the milling cutter (figure 12), when cutting off stock, or when milling
comparatively deep or long slots.
(c)
The direction of cutter rotation is related to the manner in which
the workpiece is held. The cutter should rotate so that the piece springs
away from the cutter; then there will be no tendency for the force of the
cut to loosen the workpiece. No milling cutter should be rotated backward
as this will break the teeth. If it is necessary to stop the machine during
a finishing cut, the power feed should never be thrown out, nor should the
workpiece be feed back under the cutter, unless the cutter is stopped or the
workpiece lowered. Never change feeds while the cutter is rotating.
e.
Cutting Oils.
(1)
The major advantage of a cutting oil is that it reduces frictional
heat, thereby giving longer life to the cutting edges of the teeth. The oil
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