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Milling Procedures

Always do research on the material you are going to cut!  The feed-rate and spindle-speed are highly dependent on material, cutter-type and setup.  Remember that machining is a dynamics problem, things are spinning, flexing and shearing.  The key to a well machined part is a rigid setup, appropriate lubrication and proper cutting forces.

Feed and Speed

Whether using the drill press or the milling center it is important to select the correct spindle speed.  Spindle speed is specified in RPM (revolutions-per-minute) and can be calculated based on the cutter diameter and the material from tables.  Tables usually list feed-rate in SFM (surface-feet-per-minute), which can be converted into RPM using the following formula, where the diameter of the tool is in inches:

RPM = [ 12 x SFM ] / [ PI x ( tool diameter ) ]

Similarly you can determine the feedrate in IPM (inches-per-minute) given a specified IPR (inches-per-revolution) from a table using the following formula:

IPM = ( # of teeth in the cutter x IPR ) x RPM

So for example if you were going to cut aluminum with a 3/8" HSS 2 flute end-mill you would want to start with a spindle speed of (12*300) / (3.1416*0.375) = 3056 RPM and feed rate of (2*0.001)*3056 = 6.1 IPR.

 Material  Speed (SFM)  Feed (IPR)
 Aluminum  300  0.001
 Brass  200  0.001
 Mild Steel  100  0.001
 Stainless Steel  50  0.001
 Teflon  250  0.002
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