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calculating spindle
speed for milling
Before calculating the spindle speed for a milling
operation, you must first understand the concept
of "Cutting speed" and how it differs from "spindle
speed."
Cutting speed is defined as the rate at which a
cutting tool's edge passes across the surface of a
workpiece. it is generally measured in "surface feet
per minute" (sfm), which represents the theoretical
distance the cutting edge would travel across the
material in a straight line in one minute.
every workpiece material type has an ideal cut-
ting speed to maximize cutting tool life, based
on the hardness and microstructure of the mate-
rial. the cutting speeds listed in figure 29 are
intended to serve as a basic guideline only. For a
high degree of accuracy, we recommend referring
to MACHINERY'S HANDBOOK or spindle speed
calculators on the web for more detailed informa-
tion.
cutting speeds for high speed steel (hss)
cutting tools
Workpiece Material
aluminum & alloys
Brass & Bronze
Copper
Cast iron, soft
Cast iron, hard
Mild steel
Cast steel
alloy steel, hard
tool steel
stainless steel
titanium
plastics
Wood
note: For carbide cutting tools, double the cut-
ting speed. these values are a guideline only.
refer to the MACHINERY'S HANDBOOK for
more detailed information.
figure 29. Cutting speed table for hss cutting
tools.
-28-
Cutting speed (sfm)
300
150
100
80
50
90
80
40
50
60
50
300-800
300-500
the cutting speeds shown in figure 29 do not
represent the recommended spindle speed in
rpM. the relationship between cutting speed and
spindle rpM is dependent on the diameter of the
installed cutting tool. When a tool's cutting edge
rotates, as is the case with a milling machine,
the cutting speed of that tool is directly propor-
tional to its diameter. tools with larger diameters
produce greater cutting speeds because each
cutting edge travels farther per revolution of the
spindle. therefore, a larger diameter cutting tool
will require a slower spindle speed to achieve the
same cutting speed as a smaller cutting tool.
to calculate the needed spindle speed in
rpm:
1.
use the table in figure 29 to find the cutting
speed required for the workpiece material.
2.
Measure the diameter of your cutting tool in
inches.
3.
use the following formula to determine the
needed spindle speed in rpM for your opera-
tion:
*
Recommended
Cutting Speed (FPM) x 12
Tool Dia. (in inches) x 3.14
*
Double if using carbide cutting tool
4.
refer to speed changes on the next page to
set your spindle speed to the position closest
to the rpM value given by the formula.
5.
during operation, adjust the feed rate by
increasing or decreasing how fast you turn
the handwheels to fine-tune the performance
of the cutting operation. to maximize tool life,
use the highest feed rate possible without
bogging down the machine or causing the
tool to chatter.
failure to follow cutting speed guidelines
when setting spindle speed may threat-
en operator and bystander safety and put
undue strain on moving parts, shorten tool
life, and create poor workpiece results.
Model G0705 (Mfg. since 09/09)
Spindle
=
Speed
(RPM)
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