Question 1

How do I convert cutting speed to spindle RPM?

Accepted Answer

Imperial: RPM = (SFM × 12)/(π × diameter). Metric: RPM = (1000 × Vc)/(π × diameter mm). Then feed rate = RPM × chip load × number of flutes. The tool also runs it backwards, from the spindle speed you can actually turn to the surface speed that gives you.

Question 2

What cutting speed should I use?

Accepted Answer

It depends on the pair, not on the operation: the workpiece material sets a band, and the tool material scales it. Carbide runs at roughly three times HSS in the same material, because what changes is how hot the edge can get before it stops being hard. Pick both on this page and you get the band for them.

Question 3

What chip load should I use?

Accepted Answer

Roughly 0.5-1% of the cutter diameter in steel, 1-2% in aluminium, and 0.3-0.6% in titanium and superalloys — so it scales with the cutter, not with the machine. Below about 0.02 mm of actual chip the edge rubs instead of cutting, which is worse for the tool than a heavier chip.

Question 4

Can I use a diamond-coated or PCD cutter on steel?

Accepted Answer

No. Carbon from the diamond dissolves into hot iron, so the tool chemically disappears rather than wears, often within seconds. Diamond is for aluminium, composites and other non-ferrous work. The calculator refuses this pair rather than giving you a number for it.

Feeds & Speeds

1 · What are you cutting, and with what?

2 · Calculator

3 · Or work backwards from the spindle