Questions about Bed Levelling with multiple Z Motors

  • Hi there!

    I'm configuring the bed levelling with multiple Z motors, but I'm not quite sure if I understood how it works correctly… this is what I understand of the process (for 2 Z motors), please correct me if I'm wrong:

    The process checks the two points I've set in bed.g file, and then physically adjust the Z motors independently moving them up or down to correct the tilt, and then, the bed should be straight in that plane.

    To start with, I'm trying to configure it in a custom Prusa I3 printer, so my understanding of this, as the bed only moves in the Y axis, and the test is performed moving Z and X, is that if the X axis is not well leveled, it will correct that (something like what Prusa is doing with the MK3, where they go up until the axis "crash" with the top of the frame).

    I've configured my Z motors position , by using M671 in config.g (M671 X-65:X265 Y80:Y80 S3). For X position, I've measured it from the position 0 and 200 (X min/max), for Y, is the result of dividing the size of my bed by 2.
    Then, I've configured in bed.g the probe points, starting with a home of Z, and ending with another homing, plus a mesh bed levelling.

    G28 Z
    G30 P0 X0 Y80 Z-99999 ; probe near a leadscrew
    G30 P1 X200 Y80 Z-99999 S2 ; probe near a leadscrew
    G28 Z

    My bed is installed over 4 springs in the corners, and what I was expecting is that the corners may be a bit up or a bit down (I tried to level them as perfect as possible), meanwhile the (0,80) and the (200,80) are aligned, however, what I see in my mesh is this:

    My feeling here is that the plane is tilted down to the right…

    Am I doing something wrong? It is correct to execute a G29 after the correction?


  • administrators

    I suggest that for the moment you leave out the G29. Run G32 and see what it says the deviation is before and after (after should always be zero if you have only 2 probe points). Then run it 2 or 3 more times and see what deviation it reports after each one. Depending on your mechanics, it may take a few runs to converge.

    There is an extra M671 parameter in firmware 1.21RC3 to help with convergence.

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