Reference
Machining formulas, ready to run.
The core speeds-and-feeds math — surface speed, RPM, feed rate, chip load, metal removal rate, and power — with live calculators. For a tool-specific recommendation, let the Speeds & Feeds calculator do it all.
Spindle speed (RPM)
RPM = (SFM × 3.82) ÷ tool diameter
Spindle speed3,056 RPM
Surface speed (SFM)
SFM = RPM × .262 × tool diameter
Surface speed393 SFM
Feed rate (IPM)
Feed = RPM × chip load × number of flutes
Feed rate24 in/min
Chip load per tooth
Chip load = feed ÷ (RPM × number of flutes)
Chip load / tooth0.002 in
Metal removal rate (MRR)
MRR = width of cut × depth of cut × feed rate
Removal rate3 in³/min
Power (HP ⇄ kW)
HP = 1.341 × kW · kW = .7457 × HP
Horsepower13.4 HP
Notes
- Calculators use inch units. For metric: RPM = (surface m/min × 318.31) ÷ diameter (mm); SMM = RPM × .003142 × diameter (mm).
- Chip load per tooth scales with tool diameter; surface speed (SFM) comes from the work material.
- These are starting points — tune to chip color, sound, and finish. The Speeds & Feeds calculator returns tested roughing and finishing numbers for your exact RobbJack tool and material.