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These are the HSS and carbide starting ranges stored in the ShopCalc material library. The RPM table applies the site’s SFM-to-RPM formula to each range.
RPM is computed at the low, midpoint, and high end of both stored SFM ranges. Diameter is the cutter diameter for milling or cutting diameter for turning.
| Tool diameter | HSS RPM | Carbide RPM | ||||
|---|---|---|---|---|---|---|
| Low · 50 SFM | Mid · 65 SFM | High · 80 SFM | Low · 180 SFM | Mid · 265 SFM | High · 350 SFM | |
| 1/8″ | 1,528 | 1,986 | 2,445 | 5,500 | 8,098 | 10,695 |
| 1/4″ | 764 | 993 | 1,222 | 2,750 | 4,049 | 5,348 |
| 3/8″ | 509 | 662 | 815 | 1,833 | 2,699 | 3,565 |
| 1/2″ | 382 | 497 | 611 | 1,375 | 2,024 | 2,674 |
| 3/4″ | 255 | 331 | 407 | 917 | 1,350 | 1,783 |
| 1″ | 191 | 248 | 306 | 688 | 1,012 | 1,337 |
The existing SFM-to-RPM calculator is preset to Ductile Iron, a 1/2-inch tool, and the 65 SFM HSS midpoint. Change any input to recalculate.
The stored starting range is 50–80 SFM for HSS tooling and 180–350 SFM for carbide tooling.
180 SFM with a 0.500-inch tool calculates to 1,375 RPM using RPM = SFM × 12 ÷ (π × diameter).
The material library stores 0.003 inch per tooth as the 1/4-inch end-mill starting chip load.
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