What surface speed should I use for knurling?

Knurling forms the metal by pressure rather than cutting, so it runs slower than turning. A surface speed of about 100 to 150 SFM works for mild steel; use the lower end for harder materials and larger diameters to limit heat and wheel wear.

How is knurling RPM calculated?

RPM equals the surface speed in surface feet per minute times 12, divided by the circumference in inches, which is pi times the diameter. So RPM = (SFM × 12) / (π × diameter), the same speed formula used for turning.

What does the tracking check do?

For the diamond pattern to close cleanly the circumference must contain a whole number of knurl teeth. The tool multiplies circumference by the wheel TPI; if that product is far from a whole number the pattern double-tracks and produces a muddy or doubled diamond.

How many passes does knurling need?

Knurling is usually formed in one to several light passes to the full depth rather than one heavy plunge. The tool divides the total form depth by a conservative infeed per pass to estimate the number of passes; reduce infeed for harder material.

Can I adjust the diameter to fix tracking?

Yes. If the circumference does not divide evenly by the knurl pitch, turning the blank a few thousandths smaller or larger to land on a whole number of teeth often fixes double-tracking. The tool shows the nearest clean diameters above and below.

Knurling RPM & Feed Calculator

Knurling forms a pattern by pressure, so it has its own speed rules and a tracking constraint that turning does not. This calculator gives the spindle RPM from a sensible surface speed, estimates infeed and passes, and checks that the diamond will actually close on your diameter.

How it works

The spindle speed uses the standard surface-speed relationship, the same one used for turning:

RPM          = (SFM × 12) / (π × diameter)
circumference = π × diameter
teeth around  = circumference × knurl TPI
passes        = ceil(total form depth / infeed per pass)

Knurling runs slow — roughly 100 to 150 SFM for steel — because it displaces metal rather than shearing it. The pattern only closes cleanly when teeth around is a whole number; otherwise the second revolution lands its teeth between the first set and you get a doubled, muddy diamond.

The tracking check

Multiply the circumference by the wheel’s teeth per inch. If the result is close to a whole number the pattern tracks. If it is not, the tool reports the nearest diameters above and below that do divide evenly, so you can pre-turn the blank a few thousandths to land on a clean count.

Example and tips

Knurling a 0.500 inch diameter at 120 SFM gives RPM = (120 × 12) / (π × 0.5) ≈ 917 RPM. With a 20 TPI wheel the circumference is 1.571 inch, so teeth around is 1.571 × 20 = 31.4 — not a whole number, so it double-tracks. Turning the blank to about 0.493 inch lands on 31 teeth exactly. Apply firm, steady infeed and flood with cutting oil; light passes that never reach full depth cause flaking.