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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

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#### By newguy

January 2, 2011, 4:51 pm

Useful info, thanks.
Can you supply more examples for diffenet cutters and materials?

#### By Eldar Gerfanov

January 2, 2011, 5:03 pm

Quote:
Useful info, thanks.
Can you supply more examples for diffenet cutters and materials?

Â Its comming later.

#### By Nam

May 12, 2017, 9:43 pm

Thanks that help me a lot.

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