General Speeds and Feeds Formulas
December 24, 2010, 3:10 pmArticle Summary
Eldar Gerfanov
December 24, 2010, 3:10 pm
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Eldar Gerfanov
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Here are basic formulas to get you going. Learn formulas to find put Spindle Speed and Feed rate for your application.
RPM=  12 x SFM  or RPM=  4 x SFM 

3.14 x Diameter  Diameter 
FR=RPM x T x CL
Imperial Defenitions
 RPM= Revolutions Per Minute, Spindle Speed, Number of revolutions of tool(for mills) or workpice(for lathes) per minute
 SFM = Surface Feet Per minute, Cutting speed, Distance which tip of tool travels per minute.
 IPM = Inches Per Minute, Feed Rate, Number of inches tool will travel along workpice per minute.
 IPR = Inches Per Revolution, Feed Rate, Number of inches Tool will traver per one revolution of spinle.
 FR = Feed Rate, Given as IPM
 T = Number of teeth on the cutter
 CL= Chip load per tooth, This is the size of chip that each tooth of the cutter takes.
Imperial Formulas
Examples are given for 0.5 inch 2 flute end mill on Steel at cutting speed = 100(ft/min), Chip Load=0.001(inch per tooth)
Spindle Speed (RPM)
Formula user for milling and drilling applications
Accurate Formula
RPM=  12 x SFM  =  12 x 100(ft/min)  =764(revs/min^{1})  
3.14 x Diameter  3.14 x 0.5(in) 
Approximate Formula
RPM=  4 x SFM  = 
4 x 100(ft/min) 
=800(revs/min^{1}) 

Diameter  0.5(in) 
For turning applications we do not need this formula since Spinde Speed is usually given in Constant Surface Speed (CSS), which uses SFM value directly. But if you still want to use RPM formula, then diameter value is the actual diameter of workpice.
Feed Rate (IPM)
Formula user for milling and drilling applications
FR=RPM x T x CL
FR=800(RPM) x 2 x 0.001 =1.6(IPM)
For turning applications we do not need this formula since FR is usually given in Inches per Revolution (IPR)
Eldar Gerfanov
By newguy
Useful info, thanks.
Can you supply more examples for diffenet cutters and materials?
By Eldar Gerfanov
Can you supply more examples for diffenet cutters and materials?
Â Its comming later.
By Nam
Thanks that help me a lot.