Machining parameter reference: speeds, feeds and cutter engagement
Exactalloy · Updated
Calculate spindle speed from surface speed and diameter, then derive feed from feed per tooth and flute count. Treat every figure as a starting point and adjust against the actual chip, sound and surface.
The two formulas you actually need
Spindle speed follows from the cutting speed you want at the edge; feed follows from the load you want on each tooth. Everything else is a correction to these two numbers.
- n (rpm) = 1000 × Vc / (π × D), with Vc in m/min and D in mm.
- F (mm/min) = fz × z × n, with fz in mm/tooth and z the flute count.
- Example: D10 cutter in carbon steel at Vc = 150 m/min gives n ≈ 4770 rpm; at fz = 0.05 and z = 4, F ≈ 954 mm/min.
Radial and axial engagement change everything
Chip thinning means the same feed per tooth produces a different load when the radial engagement is small. Deep axial and light radial passes let you raise the feed and take heat away with the chip.
- Full-width slotting is the heaviest case; reduce feed accordingly.
- Below about 30% radial engagement, increase feed per tooth to compensate.
- Dynamic milling trades radial width for axial depth and keeps the load constant.
Diagnosing the result
The cut tells you which way to move. Change one variable at a time and keep the engagement constant while testing.
- Thin or powdery chips: feed is too low for the speed.
- Blue or discoloured chips on steel: speed or cooling is too aggressive.
- Chatter or a ringing sound: reduce radial engagement or shorten the overhang.
- Rapid edge wear or chipping: re-check runout before changing the grade.
What the shop must supply
A catalogue dimension is not a cutting recommendation. To receive usable starting data, supply the conditions the tool will actually run in.
- Machine model and spindle interface, and its maximum speed.
- Workpiece material and measured hardness.
- Operation, feature drawing and required tolerance and finish.
- Coolant type and pressure, and the holder in use.
- Preferably the current parameters and the observed problem.