Would you use a feed rate for rotary axes in mm/min (surface speed)?

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30 Sep 2026 08:15 #350002 by grandixximo
I'm deciding whether to work on a LinuxCNC feature and would like to know first whether anyone would actually use it.

Today, when a rotary axis moves together with X, Y or Z, F applies to the linear axes only, and a rotary move on its own runs at F in degrees per minute. On a 4th-axis wrap, where the surface of a cylinder is cut with X and A, the surface speed therefore doesn't match F. The usual workaround is inverse time (G93) from the CAM.

The idea is a reference radius for each rotary axis, set in the INI. For example, `[AXIS_A] FEED_RADIUS = 25` puts A in the feed calculation as if it were a length at 25 mm from its centre. A move of A alone at F100 would then run at 100 mm/min on the surface at that radius, and X with A would run at F along the combined path. Siemens (FGREF) and Fanuc (a parameter) do the same.

Questions:
1. Would you use this, or does G93 from your CAM already cover it for you?
2. What machine: 4th-axis wrap, rotary table, something else?
3. The useful radius is usually the stock radius, which changes per job. Is a fixed INI value good enough, or would you need to set it from G-code?

A short "yes, I'd use it", "no" or "G93 is fine" helps. If nobody needs it, I'll leave it.

 

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