Cutoff & Grooving Cycle Time Calculator

Inputs

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Bar or shoulder OD where the plunge begins.
in
0 for a full cutoff to center; the groove root diameter for grooving.
in
Programmed constant surface speed (G96). Carbide parting steel commonly runs a few hundred SFM — the insert maker governs.
SFM
Radial plunge feed. 0.0508 mm = 0.002 in/rev is a common parting start point.
in
The G50/G92 spindle-speed clamp (or machine maximum) — chuck and workholding limits often set it lower than the spindle can spin.
rpm

Results

Default result
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Plunge cycle time (t)
0.348 min

CSS saves 18.4 s over a constant 764 RPM cut — the spindle spends the saving by accelerating as the radius shrinks.

Feed-on time for one plunge; approach, retract and multiple grooving passes add to it.

Also computed

RPM clamp kicks in at (d_c) Pass 0.509 in

Most of the plunge runs at true constant surface speed; the clamped tail near center is short.

Below this diameter the spindle is pegged at max RPM and surface speed falls.

Time in clamped phase 0.0424 min

RPM at start diameter (n_0) 763.9 rpm

Same cut at constant RPM 0.654 min

Spindle fixed at the OD-safe speed the whole way — the G96 comparison.

Method notes 4 notes
  • Exact integral of dr/(f·n(r)) — the R² term is why parting a 2× larger bar takes ~4× longer, not 2×.
  • Feed-on time for a single plunge only: approach, pecks, retracts, and the multiple stepped plunges of a wide groove multiply it.
  • The clamp is usually workholding, not the spindle: program the G50/G92 limit your chuck and part stick-out actually permit.
  • Many shops drop feed near center where the clamped surface speed gets slow — that conservatism adds to this idealized figure.

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