An end mill chip load calculation gives you programmed feed per tooth from feed rate, spindle speed, and effective tooth count. Divide feed rate by RPM times effective tooth count, using the effective tooth count for the tool.
End Mill Chip Load Calculation Formula
Feed per tooth is the programmed advance per effective tooth. Calculate it by dividing feed rate by spindle speed multiplied by effective tooth count. To find feed rate from a known feed per tooth, multiply feed per tooth by spindle speed and effective tooth count. Keep feed rate units consistent with the distance unit used for feed per tooth.
| Symbol | Meaning | Units |
|---|---|---|
| fz | Programmed feed per tooth | mm/tooth or in/tooth |
| vf | Feed rate | mm/min or in/min |
| n | Spindle speed | RPM |
| z | Effective tooth count | teeth |
fz = vf ÷ (n × z)
vf = fz × n × z
Metric Calculation Example
With a feed rate of 600 mm/min, spindle speed of 6,000 RPM, and 4 effective teeth:
fz = 600 ÷ (6,000 × 4) = 0.025 mm/tooth
This is the programmed feed per tooth. Reversing the calculation gives 0.025 mm/tooth × 6,000 RPM × 4 teeth = 600 mm/min.
Imperial Calculation Example
With a feed rate of 24 in/min, spindle speed of 8,000 RPM, and 3 effective teeth:
fz = 24 ÷ (8,000 × 3) = 0.001 in/tooth
The result is in inches per tooth because the input feed rate is in inches per minute. These arithmetic examples illustrate the formula only. They do not set cutting parameters for a particular tool or job.
Programmed Feed and Chip Thickness
Programmed feed per tooth is the commanded advance per tooth pass. Actual chip thickness can vary with engagement and tool geometry. A light radial cut can produce a thinner chip than the programmed feed per tooth suggests. For more on chip thickness compensation, see chip thinning in milling.
The end mill selection guide covers factors that help frame tool choice. Before using a calculated feed rate, check that the feed units, programmed RPM, and effective tooth count match the values in your setup.
FAQ
What Does Fz Mean?
fz is programmed feed per tooth, expressed in millimeters per tooth or inches per tooth.
What If RPM or Tooth Count Is Zero?
The calculation is undefined if RPM or effective tooth count is zero, because either value makes the denominator zero.
Is Feed per Tooth Actual Chip Thickness?
No. Feed per tooth is programmed. Actual chip thickness can vary with engagement and tool geometry.