Why does a narrower stepover let me cut deeper?

Because spindle power follows removal rate, which is stepover × depth × feed. Halve the stepover at the same feed and the same power carries twice the depth, the trade deep, light-stepover roughing relies on.

How much spindle power should I hold in reserve?

That is your call; the calculator adds none of its own. Enter the power-curve value at your RPM minus the reserve your shop keeps, and every result follows from it.

What if power allows more depth than my flute length?

Then flute length sets the depth, and the spindle load at usable depth shows the power left over. Spend it on feed or stepover within the catalog chip load rather than cutting past the flutes.

Does this work for face mills or turning?

Face mills, yes: enter width of cut as radial depth and the insert's maximum depth of cut as flute length. Turning removal rate is cutting speed × feed per revolution × depth, so it needs a turning power check.

CNC Machining calculator

Depth of Cut Calculator

Plan how deep each roughing pass can go before the spindle runs out of power. You need spindle power at your RPM, drive efficiency, the material's unit power, stepover, feed and flute length.

What this calculator does

Deepest axial pass your spindle power supports at a set stepover and feed, checked against the end mill's flute length.

Formula used

Cutting power per inch of depth = unit power × radial depth of cut × feed rate
Power-limited axial depth = available spindle power × drive efficiency ÷ 100 ÷ cutting power per inch of depth
Usable axial depth = the smaller of power-limited axial depth and flute length
Removal rate at usable depth = usable axial depth × radial depth of cut × feed rate
Spindle load at usable depth = usable depth × cutting power per inch ÷ (drive efficiency ÷ 100) ÷ available power × 100

Inputs explained

Available Spindle Power: Power-curve value at your RPM, less any reserve you keep.
Spindle Drive Efficiency: Share of motor power that reaches the cutter, from the machine manual.
Unit Power: Handbook value for the material; about 0.3 aluminum, 1.0 stainless.
Radial Depth of Cut: Stepover from the CAM toolpath, measured across the cutter.
Feed Rate: Programmed cutting feed at that stepover.
Flute Length: Length of cut from the end mill catalog.

How to use the result

Best suited to splitting a deep pocket into roughing passes, moving a proven cut to a smaller machine.
Power is one limit; stickout, deflection, chatter and chip evacuation can cap depth sooner. Handbook unit powers are for a 0.25 mm (0.010 in) chip; enter a higher value for thinner chips.

Current U.S. benchmarks

The producer price index for steel mill products stands at 381.162 (BLS, Aug 2026), up 23.4% from a year earlier. Quotes priced off last quarter's material cost miss this move.
The U.S. has 17,154 machine shops establishments employing about 223,303 workers (Census County Business Patterns, 2023).

Common questions

Why does a narrower stepover let me cut deeper? Because spindle power follows removal rate, which is stepover × depth × feed. Halve the stepover at the same feed and the same power carries twice the depth, the trade deep, light-stepover roughing relies on.
How much spindle power should I hold in reserve? That is your call; the calculator adds none of its own. Enter the power-curve value at your RPM minus the reserve your shop keeps, and every result follows from it.
What if power allows more depth than my flute length? Then flute length sets the depth, and the spindle load at usable depth shows the power left over. Spend it on feed or stepover within the catalog chip load rather than cutting past the flutes.
Does this work for face mills or turning? Face mills, yes: enter width of cut as radial depth and the insert's maximum depth of cut as flute length. Turning removal rate is cutting speed × feed per revolution × depth, so it needs a turning power check.

Last reviewed 2026-10-01.