End Mill Speeds and Feeds Calculator
An end mill speeds and feeds calculator resolves end mill geometry plus workpiece material into two numbers every CNC control reads: spindle RPM and feed rate. This calculator adds chip load, SFM, metric cutting speed, and material removal rate, with a chip-thinning correction applied when radial engagement is less than half the tool diameter. Works equally well as an end mill speeds and feeds calculator metric setup for shops that program in mm/min.
The end mill formulas
- RPM = (SFM x 12) / (pi x D) in imperial, or RPM = (Vc x 1000) / (pi x D_mm) in metric.
- Feed rate (IPM) = RPM x chip load x flutes, or feed rate (mm/min) = IPM x 25.4.
- MRR = axial depth x radial depth x feed rate.
For a 3/8 inch 3-flute carbide end mill in 4140 alloy steel (280 SFM, 0.0015 IPT): RPM = (280 x 12) / (pi x 0.375) = 2,852. Feed rate = 2,852 x 0.0015 x 3 = 12.8 IPM. At 0.1 inch axial and 0.188 inch radial (half slot), MRR = 0.1 x 0.188 x 12.8 = 0.24 in^3/min.
SFM reference
| Workpiece | HSS SFM | Carbide SFM | Vc (m/min, carbide) |
|---|---|---|---|
| Aluminum 6061 | 600 | 1400 | 427 |
| Mild steel 1018 | 100 | 400 | 122 |
| Alloy steel 4140 | 70 | 280 | 85 |
| Stainless 304 | 60 | 220 | 67 |
| Stainless 316 | 50 | 200 | 61 |
| Titanium Ti-6Al-4V | 40 | 120 | 37 |
| Inconel 718 | 20 | 80 | 24 |
| Plastic (Delrin) | 800 | 2000 | 610 |
Chip thinning and HSM toolpaths
When radial engagement drops below half the tool diameter, the actual chip thickness is thinner than the programmed IPT and feed must rise to restore target chip thickness. The Sandvik chip-thinning factor D / (2 x sqrt(Ae x (D - Ae))) is the industry-standard correction. At Ae = 0.05 inch on a 0.5 inch end mill (10 percent radial) the factor is 1.67x. HSM and trochoidal milling strategies rely on this correction to run 2-3x faster than conventional slot milling without burning the tool.
End mill speeds and feeds calculator metric
For an end mill speeds and feeds calculator metric workflow, this calculator returns feed rate and cutting speed in mm/min and m/min alongside the imperial values. Enter diameter and depths in mm via the unit toggle; all outputs return in both systems. Metric users in the EU, UK, Japan, and Australia can paste mm/min feeds straight into their G-code. The chip-thinning correction is unit-independent.