Cutting speed to RPM calculator
Surface speed is a property of the material and the tool. Spindle speed is what you dial in, and it depends on diameter.
m/min
Mild steel with HSS about 30; with carbide 150. Aluminium 300 or more.
Spindle speed
3183rpm
- Feed rate
- 636.6 mm/min
- Feed rate in inches per minute
- 25.064
- Surface speed in feet per minute
- 328.1
- Feed per revolution
- 0.2000
- Rough material removal rate For a full-diameter, full-depth slot.
- 64 mm3/min
Show the working
- Surface speed = 100
- Tool or work diameter = 10
- Number of flutes = 4
- Chip load per tooth = 0.05
- Spindle speed = 100 * 1000 / (pi * 10) = 3183.1
- Feed rate = 3183.1 * 4 * 0.05 = 636.62
- Surface speed in feet per minute = 100 * 3.280839895013123 = 328.084
- Feed per revolution = 4 * 0.05 = 0.2
- Rough material removal rate = 636.62 * 10 * 10 / 1000 = 63.662
- Feed rate in inches per minute = 636.62 / 25.4 = 25.0638
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- rpm = surface speed x 1000 / (pi x diameter in mm)
- feed rate = rpm x flutes x chip load
Chip load matters more than feed rate. Too light a chip rubs instead of cutting and work-hardens the material.
Surface speeds are a starting point from the tool maker, not a law. Rigidity, coolant and depth of cut all move them.