Speeds and Feeds
Speeds vs Feeds
Although they sound similar, they are
very different.
Speed refers to the rotational speed of
the spindle.
Feed refers to the linear speed at which
the tool is fed into the material.
Spindle Speed
Spindle speed is a
rotational speed
or angular velocity
It is measured in
revolutions per minute (rpm)
Calculating Spindle Speed
To calculate the proper spindle speed
the following must be known:
The material to be cut
The material of which the tool is made
The type of operation being performed
The diameter of the tool
Cutting Speed
Cutting speed is a value which is
determined using
The material to be cut
The material of which the tool is made
The type of operation to be performed
Cutting Speed is measured in feet per
minute (fpm).
Cutting Speed
The cutting speeds may be found in a
reference table like that in the
Machinery’s Handbook.
Calculating Speeds
Knowing the cutting speed (CS) and the
size of the tool, spindle speed may be
found using the following equation:
CS *12
N
 * dia
or
CS * 4
N
dia
Example
Find the spindle Speed (N) for the
following:
Material to be cut = 1018 mild steel,
annealed
½” High Speed Steel (HSS) end mill
From the table the
cutting speed is
110 fpm
Calculation
By substitution
and solving we
get:
CS * 4
N
dia
110 * 4

.5
 880rpm
Rate of Feed
Remember that this is the linear speed
at which the material is fed into the
tool.
It is found using the equation
Fm = ft x nt x N
Fm = Feed rate in inches per minute
ft = feed in inches per tooth (obtained from a
Machinery’s handbook)
nt = number of cutting teeth on the tool
N = Spindle speed (CS x 4 / D)
Example
Find the correct rate of feed for the
following:
Material to be cut = 1018 mild steel,
annealed
1/4” High Speed Steel (HSS) end mill
Find the Information
Find the
rate of feed
in the table.
.004 in/tooth
Calculations
CS * 4
N
dia
110 * 4

.25
 1760rpm
Fm  f t * n t * N
 .004 * 2 *1760
 14.08ipm
Purpose
The purposes for using the correct
spindle speed and rate of feed are:
To extend tool life
Promote fast cutting
Produce parts at lower cost