Machining Formulas

Common machining formulas can be found below.

We also have a few handy calculators to help with some of these calculations. Click here for the Machining Calculators.


Cutting Speed Formulas Mill or Lathe

(RPM = Revolutions Per Minute)  3.82 x SFM ÷ Diameter

(SFM = Surface Feet Per Minute )  0.262 x Diameter ( Tool or Stock ) x RPM


Metric Conversion

(SFM to Surface Meters Per Minute) SFM x .3048

(Surface Meters Per Minute to SFM) SMPM x 3.2808399


Metal Removal Rate

MRR =12 × DOC × Feed × SFM


Milling Feed Rate Formulas

Inches Per Minute (IPM) = FPT x T x RPM

Feed Per Revolution (FPR) = IPM ÷ RPM

Feed Per Tooth (FPT) = IPM ÷ (RPM x T)


Metric Conversion

Convert Inches Per Revolution (IPR) to Inches Per Minute (IPM) = IPR x RPM

Convert Inches Per Minute (IPM) to Inches Per Revolution (IPR) = IPM ÷ RPM

Convert Inches Per Revolution (IPR) to Millimeters Per Revolution (MMPR) = IPR x 25.40

Millimeters to Inches = Millimeters x .03937 = Inches

Inches to Millimeters = Inches x 25.4 = Millimeters

Meters to Inches = Meters x 39.37 = Inches

Inches to Meters = Inches x .0254 = Meters

Meters to Feet = Meters x 3.2808 = Feet

Feet to Meters = Feet x .3048 = Meters

Meters to Yards = Meters x 1.0936 = Yards


Milling Formulas

(CTM = Cutting Time in Minutes)  L ÷IPM

(CTS = Cutting Time in Seconds)  L ÷IPM x 60

(IPM = Inches per Minute)  RPM x IPT x # of Teeth (flutes)

(MRR = Metal Removal Rate /Cubic Inches per Minute)  W x D x IPM

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I love the speed and feed info in the back of the book. I use it on a daily basis. GARR cutters perform outstanding and are usually about 10% cheaper than the competitors. We can always get our GARR tooling within 2 days from our local distributor. -CNC Programmer / Machinist
When our inside and outside sales teams are asked, GARR TOOL customer service is always at or near the top. Always quick to respond with a clear understanding of the urgency involved. -Distribution Company Manager
Customers have confidence when using GARR TOOL. They know the quality and performance of the tool will be there, and they appreciate the level of service and pricing they receive. -Distribution Company Vendor Management / Sales Development
I was directed to GARR TOOL by a customer 34 years ago. Solid carbide tooling was very new to the industry at that time. It was obvious that carbide would soon replace HSS and Cobalt tooling. We were very impressed with GARR TOOL’s product offering. GARR TOOL was the type of company we wanted to partner with: quality products along with honest and trustworthy people. That remains the same today as well! -Distribution Company Vice President
GARR TOOL is a fantastic place to work, with competitive wages, outstanding benefits, and family values. We manufacture quality tools consistently. We don’t just offer a manufacturing job; it’s a career! -Manager at GARR TOOL

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