Spindle horsepower needed for a cut is the material removal rate multiplied by the unit power (specific cutting energy) of the material. Tougher metals need more horsepower per cubic inch removed.
What the variables mean
| Symbol | Meaning |
|---|---|
| HP | Spindle horsepower required |
| MRR | Material removal rate (in³/min) |
| P | Unit power for the material (HP per in³/min) |
Typical unit power
| Material | Unit power P (HP per in³/min) |
|---|---|
| Aluminum | 0.3 |
| Cast iron | 0.5 – 0.8 |
| Mild steel | 1.0 |
| Alloy steel | 1.1 – 1.4 |
| Stainless steel | 1.3 – 1.5 |
| Titanium | 1.1 – 1.3 |
Worked example
FAQ
What happens if a job’s required horsepower exceeds the machine’s spindle rating? The spindle will bog down, stall, or trip an overload protection, and even before that point, cutting parameters that approach the machine’s power limit tend to produce chatter and poor finish.
Does spindle horsepower requirement change with material? Yes, significantly. Harder, tougher materials require more specific cutting energy per unit of material removed, so the same material removal rate can demand very different horsepower depending on the material.
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