VBits feeds and speed

I’m new to the CNC world and I figured out feeds and speeds for milling but how do you figure out 60,90 degree and fine detail bits

Personally, I watch and listen to my machine adjusting accordingly until I just know the sweet spot for each bit on my machine.

Some bit manufacturers (amana) provide setting recommendations :man_shrugging:

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The exact RPM is not always needed, a close approximation will work (using 3 for the value of {\displaystyle {\pi }}{\pi }).

{\displaystyle RPM={CuttingSpeed\times 12 \over \pi \times Diameter}}RPM = {Cutting Speed\times 12 \over \pi \times Diameter}

e.g. for a cutting speed of 100 ft/min (a plain HSS steel cutter on mild steel) and diameter of 10 inches (the cutter or the work piece)

{\displaystyle RPM={CuttingSpeed\times 12 \over \pi \times Diameter}={12\times 100ft/min \over 3\times 10inches}={40revs/min}}RPM = {Cutting Speed\times 12 \over \pi \times Diameter} = {12 \times 100 ft/min \over 3 \times 10 inches} = {40 revs/min}

and, for an example using metric values, where the cutting speed is 30 m/min and a diameter of 10 mm (0.01 m),

{\displaystyle RPM={Speed \over \pi \times Diameter}={1000\times 30m/min \over 3\times 10mm}={1000revs/min}}{\displaystyle RPM={Speed \over \pi \times Diameter}={1000\times 30m/min \over 3\times 10mm}={1000revs/min}}


However, for more accurate calculations, and at the expense of simplicity, this formula can be used:

{\displaystyle RPM={Speed \over Circumference}={Speed \over \pi \times Diameter}}RPM = {Speed \over Circumference}={Speed \over \pi \times Diameter}

and using the same example

{\displaystyle RPM={100ft/min \over \pi \times 10,inches\left({\frac {1ft}{12,inches}}\right)}={100 \over 2.62}=38.2revs/min}RPM = {100 ft/min \over \pi \times 10 , inches \left ( \frac{1 ft}{12 , inches} \right )} = {100 \over 2.62} = 38.2 revs/min

and using the same example as above

{\displaystyle RPM={30m/min \over \pi \times 10,mm\left({\frac {1m}{1000,mm}}\right)}={1000*30 \over \pi *10}=955revs/min}RPM = {30 m/min \over \pi \times 10 , mm \left ( \frac{1 m}{1000 , mm} \right )} = {100030 \over \pi10} = 955 revs/min


  • RPM is the rotational speed of the cutter or workpiece.
  • Speed is the recommended cutting speed of the material in meters/minute or feet/min
  • Diameter in millimeters or inches.

Wow that’s some good info from you guys

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