Issue with Z-homing, not sure if its a bug or something to work around

  • I've had this happen a half dozen times and I couldn't figure out what was going on until I noticed a clue just now when I was switching tools to unload some filament.

    I'm running a dual-extruder system (e3d Chimera).

    My setup (created with RRF Configurator) defines my Z-probe offset as X-21 (its to the left of tool 0). Tool 1 is at X+18. The Z-homing is set to probe at X36 Y15, which ensures the probe is above the PEI sheet.

    What I've found is that when I switch between tools, the location the printer thinks its at changes by X+18 – which makes sense. If tool 0 is at 100, tool 1 is at 118.

    The problem is at that point, if anything attempts a Z-home/Z-probe, the printer moves back to X36Y15, but that's tool 1's X36, not tool 0's X36 -- its actually at X18, which puts the BLTouch probe off the side of the PLA by 3mm. When it raises the bed, it misses the probe, crashes the nozzles into the bed, and everything goes badly downhill from there. (The PEI sheet is thicker than the 1.7mm probe distance, so it never triggers... I've broken flex couplings because of it!)

    So what I'm not sure about is if this would be considered a bug -- the system is told to probe at 36,15, and it should know that's relative to a non-offset tool, or if I should just add things into homez and homeall to ensure tool 0 is selected first. I can obviously do that latter, but I'm not sure if there's other places in the system where something may be mis-assuming where 0,0 is in the real world because of the tool offsets.

  • Anyone have any thoughts on this? I'll just enter it as a bug over on Github, but I was curious what other people thought. I can't think of a justification for it not being a bug, though …

  • I haven't thought this through properly but one possibility that comes to mind is that the "R" parameter has changed in firmware 1.19 onwards. Do you use "G1 R" in any form in your tool change macros? If so, and if you are using firmware 1.19, you now have to specify which axes the restore points are used on. Dunno - haven't thought it through but if you use "G1 R" in you tool change macros, you may have to play around with the X Y and Z coordinates.


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