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# FEED RATES

Horizontal mill feed rates are expressed in inches per minute
(ipm) and are calculated by the formula

Table K-3 Feed in Inches per Tooth (Instructional Setting)

To calculate a feed rate, first find rpm by the preceding
formula, then refer to Table K-3 and calculate the feed rate
from the equation Information on
how the feed per tooth compares with the actual chip thickness
per tooth
To calculate the starting feed rate, use the low figure
from the feed-per-tooth chart, and if conditions permit,
increase the feed rate from there. The most economical cutting
takes place when the most cubic inches of metal per
minute are removed and a long tool life is obtained. The tool
life is longest when a low speed and high feed rate are used.
Avoid feed rates of less than .001 in. per tooth because this
will cause rapid dulling of the cutter. Exceptions to this limit
are small-diameter end mills when used on harder materials.
The depth and width of cut also affect the feed rate. Wide
and deep cuts require a smaller feed rate than do shallow,
narrow cuts. Roughing cuts are made to remove material
rapidly. The depth of cut may be in. or more, depending
on the rigidity of the machine, the setup, and the horsepower
available.

Finishing cuts are made to produce precise
dimensions and acceptable surface finishes. The depth of cut
on a finishing cut should be between .015 and .030 in. A
depth of cut of .005 in. or less will cause the cutter to rub
instead of cut and also results in excessive cutting edge wear.

The rated horsepower (hp) of a milling machine is not the
same as the horsepower available at the cutter. The horsepower
at the cutter varies from 50 to 80 percent of the input
horsepower. Thus, a 5-hp milling machine has an available
cutter horsepower of 2.5 to 4 hp. Another factor in horsepower
calculation is the material removal constant expressed in

From this example we see that a milling machine with a rating
of at least 5 hp is necessary, because it is the next size of
electric motor larger than 3 hp. Because of friction losses in
the power train, the machine will require much more than
the calculated 2.88 hp.

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