Feed Rate Calculator
Calculate milling feed rate in IPM or mm/min from RPM, chip load, and number of flutes. Instant results for CNC milling operations.
Introduction
The Feed Rate Calculator is an essential utility for determining the linear travel speed of a cutting tool during a milling or drilling operation. Precise feed rate control is paramount to achieving the target 'chip load'—the thickness of the material removed by each individual cutting edge (flute). Incorrect feed rates can lead to catastrophic tool failure: feeding too slowly causes friction and work hardening, while feeding too quickly overloads the tool, causing it to snap or stall the spindle. This tool helps you find the 'sweet spot' for maximum productivity and tool health.
How it Works
The calculation is based on the formula: IPM = RPM × Chip Load (IPT) × Number of Flutes. For metric users, the formula is mm/min = RPM × Chip Load (mm/tooth) × Number of Flutes. The calculator takes into account the spindle speed (already determined by your cutting speed calculation) and the manufacturer's recommended chip load for your specific tool and material. By adjusting these variables, you can see how changes in flute count or RPM affect the required table feed, allowing for precise synchronization of the CNC's axes.
Usage Scenarios
- Roughing a 6061-T6 pocket with a 1/2 in 3-flute carbide endmill at 800 SFM: RPM = 6,112; chip load 0.005 in/tooth; feed = 6,112 × 0.005 × 3 = 91.7 IPM. The 3-flute geometry maximizes chip evacuation room in aluminum, which is critical to prevent re-cutting.
- Finishing a 304 stainless contour with a 1/4 in 4-flute coated endmill at 150 SFM: RPM = (150 × 12) / (π × 0.25) = 2,292; chip load 0.001 in/tooth; feed = 2,292 × 0.001 × 4 = 9.2 IPM. The low chip load is the minimum to stay above the rubbing threshold for stainless.
- Drilling 1018 steel with a 0.25 in HSS twist drill at 90 SFM: RPM ≈ 1,375; recommended feed per revolution (IPR) ≈ 0.005 in; feed = 1,375 × 0.005 = 6.9 IPM. Drills use feed per revolution, not per tooth, because the two lips share the load.
FAQ
What chip load (feed per tooth) should I start with for common end mills?
Approximate starting chip loads for carbide endmills: 1/8 in dia 0.0005–0.001 in/tooth, 1/4 in dia 0.001–0.002 in/tooth, 3/8 in dia 0.002–0.003 in/tooth, 1/2 in dia 0.003–0.005 in/tooth, 3/4 in dia 0.004–0.006 in/tooth, 1 in dia 0.005–0.008 in/tooth. Soft materials (aluminum, brass) take the high end; tough materials (stainless, titanium) take the low end. HSS uses about 50–70% of carbide values.
Why does feed rate need to change every time RPM changes?
Feed rate IPM is locked to RPM by the formula IPM = RPM × chip load × flutes. If you raise RPM to chase higher SFM at a larger diameter but leave IPM the same, the chip load drops below the rubbing threshold and the tool burns up. If you raise RPM and forget to lower IPM, chip load spikes and you risk breakage. The disciplined workflow is: pick SFM, calculate RPM from diameter, pick chip load, calculate IPM. Recalculate every step when any input changes.
Should I use IPM or mm/min?
Match your CAM system and machine controller. North American shops with imperial-marked machines use IPM; European, Asian, and most metric-tooled shops use mm/min. The conversion is 1 IPM = 25.4 mm/min. Never run an unconverted value — entering 100 IPM on a controller expecting mm/min results in 100 mm/min (about 4 IPM) and a rubbing-induced tool failure within minutes. Match units across the whole tool path before posting code.