Comp in Mach3 has several bugs. Based on your code, it appears that it doesn't like G92 (or G52)
I've been carefully reading the maual to see if I can make sense of this problem and maybe it's contained in the first paragraph regarding G92 Offsets.
10.7.27 G92 Offsets - G92, G92.1, G92.2, G92.3
See the chapter on coordinate systems for full details. You are strongly advised not to use
this legacy feature on any axis where there is another offset applied.
Is it that because I used G92 to reset the origin values, and then applied G42, which is another offset, that the system throws a wobbly? It sounds like it is as rad. comp worked fine with BR529's program without G92.
It also would explain why tool length comp works without a problem in my original program as the Z axis was not offset.
If the above is the case then it's a pretty big bug indeed.
You mentioned G52 although I didn't use it. As far as I can work out, G52 seems to be similar to G92 but uses relative values instead of absolute.
Is this right or have I misunderstood this?
I'll have to experiment with it to see if it is compatible with G41/42 codes although it's less convenient than using absolute values as with G92.
Maybe G42 will work with fixture offsets? (G54 - G59) There is a warning in the manual not to call these while cutter compensation is active but is silent regarding the reverse situation.
I take on board your comments regarding the state of Mach3.
They don't exactly make me very enthusiastic to part with money for what is apparently a legacy program.