Radial Chip Thinning Calculator

Inputs

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End mill diameter.
in
Radial stepover (WOC). Thinning only happens below half the diameter — HSM/trochoidal paths commonly run 5-15% of D.
in
The chip thickness the tool maker rates (feed per tooth at half-diameter or slotting engagement). 0.0508 mm = 0.002 in.
in
Teeth on the cutter.
flutes
From the SFM for your tool and material — the SFM to RPM calculator converts it.
rpm

Results

Default result
Edit inputs
Programmed feed per tooth(f_z′)
0.00333in
Pass

The chip thins to 60% of programmed feed at this stepover — the compensated feed restores the rated load.

What goes in the program so the chip actually measures the rated load.

Also computed

Compensated table feed(V_f)106.7in/min

Naive (uncompensated) feed at the same RPM would be 1626 mm/min — thinning is unused capacity, not a safety margin.

Chip thinning factor(h/f_z)0.6

Actual max chip thickness per programmed feed; 1 at or above half-diameter engagement.

Engagement angle(θ)36.9°

Method notes 4 notes
  • Geometry-only chord relation: h_max = f_z·√(1 − (1 − 2ae/D)²). It assumes a straight-flute approximation and conventional/climb side milling; ballnose tip engagement adds axial thinning handled separately.
  • Run the chip load the tool maker rates — thinning below it work-hardens, rubs and recuts; that is why light-stepover HSM paths feed so much faster than they look like they should.
  • Tool runout adds to and subtracts from each tooth’s chip; at very light chips it dominates — keep runout under ~10% of the programmed feed per tooth.
  • Heat follows chip thickness: a properly thinned-and-compensated cut carries heat away in the chip at a lower engagement angle, which is the whole HSM bargain.

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