Reamer Feed and Speed Calculator
Reaming is a finish-sizing operation, not a material removal operation, so it runs at roughly one-third of the SFM used for drilling the same material. Pushing a reamer too fast glazes the flutes and oversizes the hole; feeding too lightly chatters and leaves a chewed-up bore. This reamer feed and speed calculator returns spindle RPM, feed per flute, feed per revolution, and linear feed rate for HSS or carbide reamers across a full range of shop materials.
The reamer feed and speed formulas
The same cutting speed equation that drives drilling and milling applies to reaming, scaled for the slower SFM a reamer expects.
- RPM = (SFM x 12) / (pi x D) where SFM is surface feet per minute and D is reamer diameter in inches.
- Feed rate (IPM) = RPM x IPR where IPR is feed per revolution.
- IPR scales with reamer diameter: the calculator takes it from reamer manufacturers' charts for your material and size, and feed per flute = IPR / flute count. Reamers use large feeds relative to drills because each flute only needs to shave a light chip.
For a 1/2 inch HSS 6-flute chucking reamer in mild steel at 50 SFM: RPM = (50 x 12) / (pi x 0.5) = 382 RPM. At the chart feed of 0.011 IPR (about 0.0018 IPT per flute), feed rate = 382 x 0.011 = 4.20 IPM. Doubled or tripled feed rates are common on rigid CNC setups once the first hole proves the tool is cutting cleanly.
Reamer SFM reference
| Material | HSS SFM | Carbide SFM |
|---|---|---|
| Aluminum | 150 | 250 |
| Mild steel (1018) | 50 | 85 |
| Alloy steel (4140) | 40 | 85 |
| Stainless steel | 30 | 75 |
| Cast iron | 50 | 100 |
| Brass | 130 | 250 |
| Titanium | 20 | 45 |
| Plastic (Delrin) | 200 | 250 |
Why reamers run so slow
A reamer is a precision tool that sizes and finishes a hole left slightly undersized by a drill or boring bar. Each flute removes a chip measured in tenths of a thousandth. Fast SFM builds heat faster than the thin chip can carry it away, and the heat softens the cutting edge and expands the hole diameter. Machinery's Handbook and the Cleveland Twist Drill reaming guide both recommend starting at half the drilling SFM and dialing up only if surface finish and hole size stay in tolerance.
Chucking, shell, and carbide reamers
A chucking reamer is the standard CNC reamer, typically 4-6 flute HSS. Shell reamers mount on an arbor and handle larger diameters (3/4 inch and up). Carbide reamers (solid or tipped) run roughly 1.5-2.5x the HSS SFM in steels and give excellent finish in hardened steels or stainless, but they chip easily if feed per flute is too high. For stainless, start around 0.006 IPR on a 1/2 inch reamer (0.001 IPT on 6 flutes), 30 SFM with HSS, and go up to about 75 SFM with carbide only after the first hole proves clean.