Thread Mill Feed Calculator

Inputs

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Internal (in a bore) or external (on a boss). The tool centre runs inside the thread for internal, outside for external.
Nominal (major) diameter of the thread.
mm
Cutting diameter of the thread mill. For an internal thread it must be smaller than the bore.
mm
Desired feed at the cutting edge — the contour / pitch-line feed from your tooling chart.
mm/min

Results

Default result
Edit inputs
Tool-centre feed(Vf·c)
120mm/min

Programmed feed at the tool centre.

Also computed

Compensation factor(k)0.4

centre slower than edge

Centre-path radius ÷ contour radius.

Method notes 4 notes
  • Internal thread: Vf_center = Vf_edge · (D − d) / D. The tool centre orbits inside the thread, so it travels a smaller circle than the cutting edge — the programmed centre feed must be reduced.
  • The factor is the radius ratio of the tool-centre path to the thread contour; multiply your charted cutting-edge feed by it to get the feed to program.
  • D is the nominal (major) thread diameter; d is the thread-mill cutting diameter.
  • Skipping this compensation makes internal threads cut too fast at the edge (the centre runs slower than the edge) — the single most-missed thread-milling setting.

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