Thread Mill Feed Calculator

Inputs

Thread type

Internal (in a bore) or external (on a boss). The tool centre runs inside the thread for internal, outside for external.

Thread major diameter (D)

Nominal (major) diameter of the thread.

Thread mill diameter (d)

Cutting diameter of the thread mill. For an internal thread it must be smaller than the bore.

Feed at cutting edge (Vf·e)

Desired feed at the cutting edge — the contour / pitch-line feed from your tooling chart.

mm/min

Default result

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.