Speeds and feeds calculator
A 12 mm cutter at 120 m/min runs at 3183 rpm, and at 0.05 mm per tooth on 4 flutes it feeds at 637 mm/min. Choose milling, turning or drilling, enter the surface speed and diameter for the spindle speed, or the speed for the surface speed, then the feed for the feed rate and the time, in metric or inch.
Turning a 50 mm bar at 200 m/min takes 1273 rpm, and 0.25 mm/rev feeds it at 318 mm/min; with the spindle clamped at 2000 rpm, constant surface speed holds 200 m/min down to Ø31.8 mm, and below that the spindle sits at the clamp. A 10 mm drill at 80 m/min runs at 2546 rpm and feeds 0.2 mm/rev at 509 mm/min.
The drawing shows the cutter, the bar or the drill turning through its circumference, and the chip it takes each turn as it feeds.
Speed ↔ RPM
Feed rate
- Spindle speed n
- Feed rate vf
How it’s calculated
RPM = 12·SFM ÷ (π·D in) or 1000·Vc ÷ (π·D mm); feed rate = RPM × chip load per tooth × flutes.
Where do the surface speed and feed come from?
From the tool maker’s data for the cutter, insert or drill and the material: they depend on the tool’s grade, coating and geometry, so no single table fits every tool. This calculator does the arithmetic once you have them. In milling, at a light radial cut the chip thins, so raise the feed per tooth to hold the maker’s chip thickness (the chip thinning calculator works it out).
Why does a lathe need a spindle limit at constant surface speed?
Constant surface speed raises the spindle speed as the tool moves in, so Vc holds as the diameter falls. Facing towards the centre, the diameter heads for zero and the speed it asks for heads for the machine’s top speed, so the program clamps the spindle. Below the diameter where the clamp is reached the spindle stays at the clamp and the surface speed falls with the diameter; the calculator gives that diameter and the surface speed reached.