Material Removal Rate (MRR)
MRR is the volume of material removed per minute. It is the direct measure of productivity — higher MRR = more parts per hour. Every cutting parameter choice should be judged against its effect on MRR.
The Formulas
Worked Example
Face milling a steel block: Vf = 600 mm/min, ap = 2 mm, ae = 40 mm. What is the MRR?
For steel at kc=3,500 N/mm², this needs about P = kc × Q / 60,000 ≈ 2.8 kW of spindle power. Check: Power & Torque Estimator
MRR and Machine Power
There is a hard ceiling: the machine spindle can only deliver so much power. If MRR × specific cutting force exceeds spindle power, the spindle bogs down or stalls.
| Machine | Typical power | Max MRR (steel) |
|---|---|---|
| Small hobby mill | 1.5 kW | ~15 cm³/min |
| Vertical machining center | 7.5–15 kW | ~60–120 cm³/min |
| Large horizontal mill | 22–45 kW | ~180–350 cm³/min |
Why this matters: you can set the fastest feed and deepest cut in the world, but if the spindle runs out of power, the tool rubs instead of cutting — and you destroy the insert. Always verify power before committing to a high-MRR program.
Calculate: MRR Calculator · Machining Time