# Lathe RPM calculator

URL: https://www.clove3d.com/tools/lathe-rpm/

Calculate optimal spindle speed for lathe turning from workpiece diameter, material and tool type (HSS or carbide). Returns a min/max RPM range, a recommended midpoint, and coolant guidance for each material.

## Formula

RPM = (Vc x 1000) / (pi x D)      [metric: Vc in m/min, D in mm]
RPM = (SFM x 12) / (pi x D)       [imperial: SFM in ft/min, D in inches]
Recommended RPM = (RPM_min + RPM_max) / 2

## Inputs

- Units: metric or imperial
- Material (10 presets or custom cutting speed range)
- Tool type: HSS or carbide
- Workpiece diameter (mm or in)
- Optional: spindle min/max limits

## Outputs

- Recommended RPM (midpoint of speed range)
- RPM range (min to max)
- Cutting speed used
- Coolant / air blast recommendation (required, recommended, or not needed)
- G-code line: S<rpm>

## Cutting speed reference (turning)

| Material                        | HSS (m/min) | Carbide (m/min) | Coolant     |
|---------------------------------|-------------|-----------------|-------------|
| Aluminium (6061 / free-cutting) | 60-120      | 200-500         | Recommended |
| Brass (free-cutting CZ121)      | 60-120      | 200-400         | Not needed  |
| Copper                          | 30-60       | 100-250         | Recommended |
| Mild steel (1018-1025)          | 18-35       | 80-180          | Recommended |
| Carbon steel (1040-1050)        | 12-25       | 60-150          | Recommended |
| Stainless steel (304)           | 8-18        | 45-100          | Required    |
| Cast iron (gray)                | 12-25       | 60-130          | Not needed  |
| Titanium (Ti6Al4V)              | 6-12        | 30-60           | Required    |
| Hard plastic (nylon, acetal)    | 100-250     | 250-500         | Not needed  |
| Wood (hardwood)                 | 200-500     | 600-1500        | Not needed  |

Sources: Machinery's Handbook, Sandvik Coromant, Seco Tools.

## FAQ

Q: How do I calculate lathe RPM?
A: RPM = (cutting speed x 1000) / (pi x workpiece diameter) in metric. Pick the cutting speed for your material and tool type, divide by the workpiece circumference.

Q: What is cutting speed (Vc or SFM)?
A: How fast the workpiece surface moves past the tool tip. Every material has a recommended range: too slow work-hardens the surface; too fast overheats the cutting edge.

Q: HSS vs carbide for turning?
A: HSS is tougher and cheaper but runs at lower speeds. Carbide runs 3 to 5 times faster but chips more easily on interrupted cuts. Use HSS on soft materials or low-power lathes; carbide when you have rigidity and power.