On Wed, 21 Dec 2022 at 12:12, Stuart Stevenson <stus...@gmail.com> wrote: > > A point and a vector fully describe a plane in 3D space.
Indeed, and you could certainly have a command to set a generic plane. But you don't need the point. G17 and friends do not define a plane, they define a continuum of planes (for example G17 is all XY planes for every possible Z) There are two discussions here that are getting mixed up. (and neither correspond to the subject any more) 1) Arbitrary arcs. There are a few ways to do this. You could certainly define an arbitrary plane then run the arc. With a normal vector defined the G2/G3 direction is well defined. But you could also specify start, end and centre (in 3D space) on one G-code line which also fully describes two possible arcs. Or (start) end and waypoint, using (XYZUVW) and (IJK) which unambiguously defines a single arc. Defining an arbitrary plane would mean that spiral arcs remain possible, but there is quite a lot of maths in defining it. End points and waypoint can be pulled off of a CAD model. There is an old "arbitrary arcs" branch, https://github.com/LinuxCNC/linuxcnc/tree/arbitrary-arc that uses magic comments to define the arc. But I think this was just a proof of concept and the plan wouldn't have been to keep that method. 2) Simultaneous curves (arcs, NURBS) for foam cutters. This would need a way to either define two end points and two centres on one G-code line, or a way to "cache" end points and centre on the line before (which would be unusual but not entirely outside the G-code paradigms). Maybe PQR for UVW centre? PQ would certainly be possible for UV arcs, re-using R would be a bit unusual for UW and VW arcs. This wouldn't work for NURBS, though, which already uses P. But perhaps Q could be used for the "secondary" plane in that case. Consistency is a problem. (Capitals are already standalone command words with a defined meaning) ABCdeFGhIJKlMNOpqRSTUVWXYZ DEH seems vaguely available. They all give an error message if used standalone. But I think I prefer PQR. -- atp "A motorcycle is a bicycle with a pandemonium attachment and is designed for the especial use of mechanical geniuses, daredevils and lunatics." — George Fitch, Atlanta Constitution Newspaper, 1912 _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
