Thanks Greg (I mentioned the build plate size to remind everyone that the 400mm size "limit" is the actual real printable output size that gcode is guaranteed to work for)
Any chance someone on the dev team could be asked to find and fix this bug? " Since your model is line-to-line to the limit of the Printable Area in the Cura Machine Settings - Cura won't slice." - that's logically wrong, of course - the only time Cura should refuse to slice is when it is *over* the limit... (I'd go as far as to say that allowing even more than the actual "limit" when any extra amount is not going to result in gcode exceeding the limit should also be allowed - e.g. 400.00005 should still be just fine (and is plausible, since floating-point-rounding...) - in fact - the build area should really be logically extended by the nozzle width as well, since we get an additional half-a-nozzle-width worth of plastic coming out on all of the sides at all times of course)
I'll try the 405 idea - but I'm not convinced that Cura is going to slice correctly still - it already refuses to do 400mm, so my guess is that it's going to output gcode that goes from 1mm to 401mm if I let it use 405mm, and I'm not sure what the Chiron firmware is going to do with that past-the-limit 401mm when it gets there...
Those grey lines around the border of my build plate suggest to me some kind of logical region that something in Cura has been told not to print in - which means Cura is *never* going to be able to print at (0,0) until we work out what those are and how to get rid of them?
Through a pile of trial-and-error, I worked out that the unprintable amount is somewhere between 1.3mm (cannot print) and 1.3001mm (slices fine) so a model that is 398.6999mm wide outputs this GCODE (which has 398.31mm extents using a 0.4mm nozzle, which looks correct):
;MINX:0.845
;MINY:199.805
;MINZ:0.2
;MAXX:399.155
;MAXY:200.195
...
G1 X399.155 Y199.805 E12.94194
G1 X0.845 Y199.805 E25.85859
...
But it proves my point - 0.845 is the smallest it can go - so something is wasting that much all around the edges.
I checked all the settings - there's no "(Home Offsets, software end stops, etc.) " (where "etc" is everything mentioning any of those things or parts of them or synonyms) - Chiron settings don't have those (not in cura, and not in firmware), and it's irrelevant since I'm looking at the gcode first.