# Feed rate help



## churchjw (Mar 18, 2013)

I am having problems figuring out the feed rate for a cnc mill.  Any help would be great.

Starting with RPM.  I am using the formula RPM = Feet per Minute/Pi*cutter diameter

So for a .500 carbide 4 flute mill cutting Aluminum Using a FPM of 900

That gives 573 = 900/3.14*.500

So 573 RPM

Then for feed I am using Feed rate in Inches Per Minute(IPM)= RPM x number of cutting edges x chip load

Using a chip load of .004"  I took that value from http://www.endmill.com/pages/training/Speed and Feed - Carbide End Mills and Drills.pdf

That gives 9.1 = 573 x 4 x .004

9.1 IPM can not be right can it?  Where am I going wrong?


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## Tony Wells (Mar 18, 2013)

Hmmm.....lessee, how many inches in a FPM?


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## churchjw (Mar 18, 2013)

Oh God is it that easy.:banghead::banghead::banghead::banghead: 

So that would be 6878 RPM = 12*900/3.14*.5

110ipm =  6878 x 4 x .004

That sounds much better.  Is it right?


Thanks Tony you are a life saver.
Jeff


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