Bed going down after autoleveling

Hi. I installed LJ18 sensor to extruder platform, turn on autolevel in firmware, set offsets.
Run gcodes:
G28 X Y
G32 S2
G28 X Y

And bed going down at ~8 mm after calibrating
I change z-probe distance settings, but didnt help
Or with numbers I need put to eeprom?

Sheme: at ~4mm near table sensor triggered


  • Why the second G28 X Y? That may cause new changes so at least for testing leave it.

    Code for leveling is in BedLeveling.cpp in function bool runBedLeveling(int s)

    As you might see there is no extra Z move programmed. At start it runs activate script and afterwards deactive probe script, which you have defined. That could of course contain z moves. As a Test run G30 at a point where activating z probe is possible. It will return z height and also run start/end script and "normally" ends up at exactly teh same position it started. Also gives you an idea if z probe height in eeprom is set right as it returns a measured z whcih you can compare with e.g. a metal block or feeler gauge.
  • So my mistake in Gcode?
    I need move Z to 0 after G32?
  • No, gcode is ok just second G28 X0 Y0 is unnecessary and might mask the source of the problem.

    But where the extra move comes form is hard to say remotely, therefor my hints on where to lock what is going on.
  • On G32 after last measuring table goes down, and leave about 10mm under extruder
  • What do M114 before and after G32 return?
    What is your start and end gcode for z probe in configuration? As I said that would be a good point that it changes.
  • 19:54:50.889: N22 G28 X0 Y0
    19:54:50.889: N23 G32 S2
    19:54:54.891: N28 M117 IP:
    19:55:02.148: X:0.00 Y:0.00 Z:0.000 E:0.0000
    19:55:02.148: Info:Autoleveling disabled
    19:55:03.543: Z-probe:2.78 X:40.00 Y:0.00
    19:55:06.238: Z-probe:2.93 X:40.00 Y:85.00
    19:55:09.220: Z-probe:3.31 X:40.00 Y:170.00
    19:55:12.963: Z-probe:3.08 X:105.00 Y:0.00
    19:55:15.949: Z-probe:3.20 X:105.00 Y:85.00
    19:55:19.108: Z-probe:3.44 X:105.00 Y:170.00
    19:55:22.988: Z-probe:3.19 X:170.00 Y:0.00
    19:55:26.130: Z-probe:3.41 X:170.00 Y:85.00
    19:55:29.615: Z-probe:3.65 X:170.00 Y:170.00
    19:55:30.964: plane: a = 0.0031 b = 0.0026 c = 2.6661
    19:55:30.971: Transformation matrix: 0.999995 0.000000 -0.003144 -0.000008 0.999997 -0.002639 0.003144 0.002639 0.999992
    19:55:30.975: CurrentZ:3.57 atZ:0.00
    19:55:30.975: Z after rotation:0.00
    19:55:30.979: Printer height:246.90
    19:55:31.586: Info:Autoleveling enabled
    19:55:32.380: X:169.99 Y:169.99 Z:4.550 E:0.0000
    19:55:40.225: N48 M114
    19:55:40.234: X:169.99 Y:169.99 Z:4.550 E:0.0000

  • You did not home Z before probing. Would at least explain 3.57mm of the drop. Have you tried the same after z homing? You can also use z probe for z homing - in fact you should if you do z min homing. Set homing order with preheat, then you set preheat temperature to 0 and can enter the probing position. That way activating z probe can be done at a position where it is possible.

    Then try again after z homing. I guess this makes a difference, also not sure what exactly.
  • No, just X-Y homing, in some cases when I do Z homing autolevel was abort because "probe triggered before measuring"
  • Yes, z probe must not be triggered when z homing starts. There is a parameter to move up before z homing to prevent just this.
  • Repetier said:
    Yes, z probe must not be triggered when z homing starts. There is a parameter to move up before z homing to prevent just this.
    Z_PROBE_BED_DISTANCE? Or witch one?
  • No ZHOME_PRE_RAISE is to go up before leveling.
  • Can't find it in Configuration.h:(
  • edited June 2018
    In the config tool.
    Under 'mechanics' endstop section,
    choose homing order X Y preheat then Z (this lets you then choose the X Y coords to goto to home Z)

    Just under the homing order, select pre raise Z axis= always and set pre raise distance to 5 .

    XY Homing pos. for Z  are preset to 99999 99999   change these to the centre of your bed.

  • Oh, im using 092, found it at 1.0

  • Set up pre-raise
    got 13:41:51.126: Error:Activating z-probe would lead to forbidden xy position: 60.000000, -55.00
  • can you post a link to your current config.h 
  • MartinH said:
    can you post a link to your current config.h

    I removed z probe offsets, looks like helping
  • 0.92 is so old and buggy regarding z-probing that I can not really help here. It is one of the big improvements in 1.0 that it fixes many z-probing issues. Not that it did not work but it had it's kinks.
  • That is 1.0
  • In your config.h you have the probe offsets at X-20  and Y+55
    So your minimum reachable probe points will be X0  Y55
    Your P1 and P2 both have Y at 0 so the printer is trying to move the nozzle -55 off the front of the bed.
    Try setting 
    P1 20  65
    P2 170 65
    P3 20 190

    Allso i would turn off 'allways check endstops' to eliminate any crosstalk on the endstop wires.

  • I changed offsets to 0
    But now got error with triggering sensor before leveling starts
  • You need to start where probe is not triggered. For homing use ZHOME_PRE_RAISE  for G32/G33 start at proper height.
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