BLTouch G30 works, homing is not?

When I run G30 P2 It correctly probes, does two attempts, and everything works fine.  When I try and run G28 or home through TS it will it the probe, back away, hit the probe a second time, stop, then ram the bed up at homing speeds.  Not sure why?  I have tried adding delays, different Z homing rates (20mm/s, 5mm/s) all behave the same.  G30 Probe works perfect so I don't think its a wiring or connection issue.  I'm guessing some timing issue with the BLTouch as I do notice during a probe it quickly jumps back after hitting the probe.  During homing its slower to jump back before hitting it the second time.  I tried higher Z Feedrates with no luck.  Any ideas?  BLTouch v 3.1


  • Also, I did run the M114 to ensure when probe is deployed and not hit a limit is low, when hit it comes back as high
  • Also, using 1.0.4
  • edited December 2020
    After putting a bunch of prints in the code, I found that at line 1980 in Printer.cpp my zCorrection was -12800 causing it to push my bed into the nozzle at the homing rate.  I'm off to bed but I'll try and figure out why its so negative and if I should even be in that method.  For now hacking it to zCorrection = 0; right before line 1980 at least proved that homing worked and I could autolevel afterwards.
    I'll update on my findings tomorrow but any tips would be appreciated :-)
  • You mean this one:
    #if Z_PROBE_Z_OFFSET_MODE == 0 // Only if measure through coating e.g. inductive
    zCorrection += axisStepsPerMM[Z_AXIS] * zBedOffset;

    zBedOffset is in eeprom called "Coating thickness [mm]" and only used during z homing to adjust coating in case you have an inductive z probe or you want some z correction to make filament stick just as you like.

    Extruder z offset of first extruder also should be 0.
  • Found it and now I feel dumb.  After printing out the corrections somehow the eeprom value for Z probe height was 40mm....  
    While I'm in the code, I might look into trying to use the same exact motions as a probe for the a home.  It seems smoother.  I don't really like using the Z home speed and it doesn't seem to drop the be as nicely between multiple probes during home as it does in a probe.

  • What do you mean with multiple probes during home? It does regular test and retest but not multiple positions. Retest is slower but you can put reduction factor to 1 to use same speed on second test as well.
  • I have to play with it more to understand better.  The test that it does (2 times) on probe is much smoother and drops smoother after the first probe and into the second test.  On a home its not as smooth and doesn't drop as far.  Its possibly just some eeprom settings (like matching the home speed to the probe speed) and some setting somewhere for the amount of drop between retries?
  • Yes could be. It is not using the probe function during homing, so it is just homing speed, go back as defined for homing and retry with homing speed/reduction factor and the move to planned z position. So that can in deed differ and look different.
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