Hey Andrew,
Do you have a sample program to test the lookahead?
Luca
On 9/30/2026 4:29 PM, andrew beck wrote:
Hey Luca
I have a 4 axis vmc. Currently biggest issues is the look ahead when
moving 4th axis with other axis as lookahead reverts to just a few blocks.
I'm not using your new scurce code on this. I use g94 for 4axis I think.
But we tried g93 also.
Definitely makes a bit difference
But this would be different again I guess
I think I would want to be able to set the dia from gcode then I would link
it in with the post processor and make it automatically set from stock dia
as you say. Might be a bit of a pain to edit ini file every time.
On Wed, 30 Sept 2026, 9:22 pm Luca Toniolo, <[email protected]> wrote:
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.
Luca
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