Some more BLtouch problems

  • Hello

    i Found some more problems with my BLtouch / Corexy printer maybe you guys have a Solution.
    Everytime i start a print with the same gcode i have a different first layer.
    Sometimes its to close sometimes to far away even if i use G29 before every print.

    Also each time i start G32 (successively)i have an deviation about 0.3
    I have tighten the Z Couppler, moving z very slow and cant measure any offset on Z moving

    Is ther a way to test the Bltouch repeatability like M48 P4 X200 Y200 V2 E L2 in marlin?

    M558 P5 X0 Y0 Z1 H5 F120 T6000 ; Set Z Probe to type Switch or Digital output
    G31 P50 X63 Y-65 Z1.8
    M557 X65:340 Y30:380 S70 ; Define mesh grid

    M584 X0 Y1 Z2:3 E4:5:6
    M671 X-75:480 Y240:240 S2

    G28 XY ; home
    G28 Z
    M401 ; deploy Z probe
    G30 P0 X65 Y190 Z-99999 ; probe near a leadscrew
    G30 P1 X370 Y190 Z-99999 S2 ; probe near a leadscrew

    M402 ; retract probe
    G28 Z

    Any idea what iam doing wrong?

  • Hey buddy.

    I'm not near my Hypercube to checks it's configuration file, but unless it's a typo on the forum I've seen something which shouldn't be there.

    In this line;

    G31 P50 X63 Y-65 Z1.8

    I'm sure the a P parameter is in the wrong place and with a too higher value.
    Looking at the advice in the wiki;


    1. In your software config.g file input the following G-Code commands to allow the setup to work:

    M307 H3 A-1 C-1 D-1 ;

    M558 P5 X0 Y0 Z1 H5 F100 T2000

    G31 X0 Y0 Z0 P25"

    Also that P parameter sets the trigger threshold as it's called, to be a little more sensitive as I think there was talk of the BLTouch giving a very fast signal when it's been activated that the Duet can miss.
    The advice from memory was to set lower than 25 so the Duet had a chance to read the BLTouch probe signal when it triggered.

    "In both cases
    Select probe type 5 (the P parameter in your M558 command), Set the G31 P parameter to a low value, because the BLTouch produces only a short output pulse, which may be filtered out if you use a higher threshold."

    So if I'm remembering right, you need to move the P parameter to the end of that line of code and also lower it's values to below 25.

    This logic falls in with your issue of having different trigger heights perhaps, possible because the P parameter is too high and in the wrong place.

    Quoted text taken from here;


  • administrators

    It doesn't matter where in the line the P parameter occurs. Also, I think all P values between about 1 and 124 will behave the same, because each time the probe output is sampled, the output from the filter will change in steps of 125.

    Reducing the probing speed sometimes helps to improve reproducibility. However, the OP is already using a low value (F120 in the M558 command).

    You can test probe reproducibility using the macros that Russ Gries published here

  • Okay so i have a 0.02 deviation in the bltouch i still lowerd the probe and the max ACC Z speed but still get a deviation around 0.19 each G32 if i do 10 times in a row

    Any ideas what i migh doing wrong?

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