The reason for Marius' original post is that he is trying to use
LinuxCNC with SheetCam's 4 axis pipe cutting module. When cutting around
the corner on square/rectangular section tubes all 4 axes are moving.
Due to the shape of the trajectory it has to be done as a series of
short G1 XYZA moves. Without lookahead these short linear moves really
slow down movement. Unfortunately this is the point where the machine
should ideally move very fast. The feed rate for each line segment is
correctly calculated to allow for any rotary movement so inverse time
mode does not help.
If you are interested, here is the original thread on the PlasmaC forum
where this issue is being discussed
<https://forum.linuxcnc.org/plasmac/49293-qtplasmac-with-fourth-axis-rotary?start=50>
Les
On 05/07/2023 11:00, andy pugh wrote:
On Wed, 5 Jul 2023 at 09:17, <marcus.bow...@visible.eclipse.co.uk> wrote:
This isn't related to the lookahead, but rather to the interpretation
of "F" for combined moves.
It is generally better (and safer) to use G93 inverse-time mode for
combined rotary and linear motions.
("Safer" because some CAM software can put a _tiny_ spurious linear
move in, and what was intended as a pure rotary motion becomes a mixed
motion with the F-word interpreted differently)
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