# Machine Shop Math - How to Calculate Spindle Speed

December 9, 2020 5:50 pm

The G-Code Tutor talks about spindle speed and explains how to calculate the correct speed based on your tool characteristics, workpiece material, and cutting feed.

Feeds and speeds are some of the most important, yet basic parameters of any give application within a machine shop. No matter how advanced your machine tool is or sophisticated your cutting tool is – if you run a program using the wrong feeds and speeds you’ll always end up with the same result: a scrapped part (and likely a broken tool). It is important, therefore, to understand how to calculate those parameters and how to use those calculations to improve your efficiency and productivity.

Spindle speed refers to the rotational speed of the machine spindle and it’s measured in RPM (revolutions per minute). Calculating the spindle speed (N) is pretty simple but in order to do so you’ll need to have the following information handy:

V = Cutting speed (typically provided by the cutting tool manufacturer and depending on the material being machined).
D= Tool diameter

Once you have this information, all you have to do is apply one the following formulas (depending on what measurement system you are working with):

Imperial system: N = (V*12)/(π*D)
Metric system: N = (V*1000)/(π*D)

To learn more about machine shop math, visit Gcodetutor.com. Stay tuned for more machining videos!

## 1 Comment

• Don says:

I was taught to calculate cutting speed in the following manner. RPM=(cutting speed for the material x 3.8) / by tool diameter for HSS tooling. Multiply the result by 3 for carbide tooling or multiply by 5 for coated carbide tooling