TECHNICAL TIP #33; END
MILLS, WHEN AND HOW MUCH TO REGRIND:
As we remove material with end
mills in the form of chips, a wear land forms on the cutting edge. When this
wear land develops to the point of generating excess heat, vibration, roughness,
or produces a part that is out of tolerance, the end mill should be
On high volume operations, a predetermined number of parts minutes
in the cut, power draw on the machine, or cubic inches of material removed can
be established as the point to pull the end mill.
When an end mill becomes
dull, we face a choice of whether to regrind or discard the end mill. This
choice is basically an economic one. Will it cost more to regrind then it
will to replace it. End mills 1/4" in diameter and above can generally be
economically reground if there are sufficient quantities to absorb setup cost.
As the diameter of the end mill is reduced through regrinding, there is a
significant reduction in the hook or radial rake angle. The original diameter
can generally be reduced by the following and still retain up to 80% of the
original cutting efficiency.
.250 thru .500 15%
.750 thru 1.00 10%
End Mills that are badly chipped or severely worn to the point that the
diameter will need to be reduced more than the above guidelines, will need to be
refluted to restore the original flute form, and radial rake angle.
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