Speed,
Feed & Depth of Cut
Speed:
The speed
at which the work moves with respect to the tool (usually measured in feet per
minute).
The
cutting speed, expressed in FPM, must not be confused with the spindle speed of
the lathe which is expressed in RPM. To obtain uniform cutting speed, the lathe
spindle must be revolved faster for workplaces of small diameter and slower for
workplaces of large diameter. The proper cutting speed for a given job depends
upon the hardness of the material being machined, the material of the tool bit,
and how much feed and depth of cut is required. Cutting speeds for metal are
usually expressed in surface feet per minute, measured on the circumference of
the work.
Feed:
It is relative velocity at which the
cutter is advanced along the work piece.feed rate is measured in mm/min. the
rate with which the workpiece under process advance under the revolving milling
cutter. It is known that revolving cutter remains stationary and feed is given
to the workpiece through worktable.
Generally feed is expressed in three
ways:
1. Feed per Tooth
It is
the distance traveled by the workpiece between engagements by two
successive teeth. It is expressed as mm/tooth(ft).
2. Feed per revolution
Travel of workpiece during one revolution of milling cutter. It is expressed as
mm/rev and denoted by F(rev).
3. Feed per unit of time
Feed can also expressed as feed/min or feed/sec. It is the
distance advances by the workpiece in unit time (fm).
Depth of cutting:
Depth of cut is
the distance that the tool bit moves into the work. usually measured in
thousandths of an inch or in millimeters. General machine practice is to use a
depth of cut up to five times the rate of feed, such as rough cutting stainless
steel using a feed of 0.020 inch per revolution and a depth of cut of 0.100
inch. which would reduce the diameter by 0.200 inch. If chatter marks or
machine noise develops, reduce the depth of cut.
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