- Spindle speed
- 3,820 RPM
- Feed rate
- 30.6 in/min
The short answer
Spindle speed RPM = cutting speed × 12 ÷ (π × tool diameter) in inch units (SFM, inches), or cutting speed × 1000 ÷ (π × diameter) in metric (m/min, mm). Feed rate = RPM × chip load per tooth × number of flutes. A 1/2-inch end mill at 500 SFM runs about 3,820 RPM; with 4 flutes at 0.002 in per tooth that is about 30.6 in/min.
Formula
RPM = (SFM × 12) ÷ (π × D) [inch]RPM = (Vc × 1000) ÷ (π × D) [metric]Feed = RPM × chip load × flutes
How to use it
- Choose inch or metric.
- Enter the cutting speed for the tool and material from the tool maker’s chart.
- Enter tool diameter, chip load per tooth and number of flutes.
Assumptions
- Starting values only: adjust for radial engagement (chip thinning), tool stick-out, workholding and machine rigidity.
- The result is capped by the machine’s maximum spindle speed if you enter it.
Frequently asked questions
Where do I get cutting speed and chip load?
From the tool maker’s recommendations for the material and tool coating. Generic charts are a starting point only.
Why does my spindle alarm on heavy cuts?
Spindle overload and overheating alarms usually mean the cut needs more power than the spindle can give at that speed. Check spindle load on the screen against the cut, then reduce depth or feed, or use a speed where the spindle has more torque.
What is chip thinning?
When the tool engages less than half its diameter radially, the actual chip is thinner than the programmed feed per tooth, so feed can be raised to restore the intended chip load.