Milling Process
Spindle Speed
 To
obtain a good finish it is essential to run
the machine at the correct spindle speed.
 Different materials have different optimum
cutting speeds (speed at which best finish
is achieved).
 This figure is the amount of material that
can pass the cutter in a given time
typically Metres/minute
Calculating Spindle Speed

Table Feed Rate

Table feed rate is the speed at which the table
can move feeding the material along the cutter
in a given period of time to produce the desired
finish typically mm/min
 Table feed rate is determined by the number of
teeth on the cutter, the chip load of the cutter
and speed of rotation of cutter.
 Chip load is the thickness of material that can be
removed by cutter teeth relating to its rigidity for
a particular material (also Known as chip
thickness).
Calculating Table Feed Rate


Table feed rate is calculated by multiplying the No of
teeth on the cutter by the chip load then multiplying the
result by the spindle speed.
Table feed rate = No of teeth x chip load x spindle speed
RPM

Example: Calculate the table feed rate in mm/min when
cutting a block of mild steel (chip load 0.125mm/tooth)
using an end mill with 4 teeth running at a speed of
742rpm.

Table feed rate = 4 x 0.125 x 742 = 371mm/min
Example
 Using
the table provided take the average
speed and chip loads and calculate:
 A)
the spindle speed in rev/min for a
Slotting Cutter (Slot Drill) 12mm diameter
cutting a slot in a block of Aluminium.
 B)
the table feed rate for the above
machining operation, slot drill has 2 teeth
Extension work
 Using
the figure obtained in example (b)
above calculate the time it would take to
cut a slot in the block of Aluminium
300mm long.