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)
0.348min

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)Pass0.509in

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 phase0.0424min

RPM at start diameter(n_0)763.9rpm

Same cut at constant RPM0.654min

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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