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Speeds & feeds: RPM and feed rate

Enter the cutting speed Vc and feed per tooth from the catalogue, the diameter and the number of flutes: Toolhelix works out the spindle speed in RPM and the feed rate in mm/min for the machine. It works for milling and, with one edge and feed per revolution, for turning. A second box converts mm/rev to mm/min and back, for live tools.

SPINDLE SPEED · n—rpm
FEED RATE · Vf—mm/min

n = Vc × 1000 / (π × D) · Vf = n × fz × z. For turning, enter 1 flute and fn per revolution.

Feed per rev or per minute

Stationary drill with the part turning: feed per spindle revolution. The same drill on a live tool, part stopped: feed per minute, from the tool rpm. Example with sample values: f 0.2 at 2500 rpm = F 500 mm/min. Type in either box and the other one updates.

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RPM formula

n = Vc × 1000 / (π × D), with Vc in m/min and D in mm. Example with sample values, not recommendations: a Ø10 end mill at Vc 180 m/min runs at about 5,730 RPM.

Feed rate formula

Vf = n × fz × z: spindle speed times feed per tooth times number of flutes. With the same example, fz 0.05 mm and 4 flutes give about 1,146 mm/min.

Feed per tooth vs feed per revolution

In milling you think per tooth (fz), because each edge cuts its own chip. In turning there is one edge and you use feed per revolution (fn): enter 1 flute and fn instead of fz.

Where cutting data comes from

Always from the manufacturer's catalogue, for that material, grade and geometry. Toolhelix only does the maths: it does not suggest working speeds and feeds, because they vary too much from case to case.

Frequently asked questions

How do I calculate end mill RPM?

Multiply the cutting speed Vc (m/min) by 1000 and divide by π times the diameter in mm. A Ø10 end mill at 180 m/min runs at about 5,730 RPM.

How do I calculate feed rate in mm/min?

RPM times feed per tooth times number of flutes. Then check it on the machine, because vibration and overhang change it.

Does lathe RPM change with diameter?

Yes: at constant cutting speed the RPM rises as the diameter falls. That is why CNC lathes use constant surface speed with a maximum RPM limit.

What cutting speed should I use for steel?

It depends on material, grade and tool. The starting value is in the manufacturer's catalogue; Toolhelix deliberately does not suggest one.

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