Mesh Bed Compensation and Bed Leveling


  • administrators

    That does seem odd. Can you arrange it so that the 4 points that you use for bed levelling correspond exactly to points on the mesh?



  • Hi @dc42

    Sure can. Will give it a go tonight when I get home from work.

    Kind Regards,

    Sam



  • Hi @dc42

    So I had a look at the actual maximum probing points for the mesh compensation and used them for the bed leveling.

    Here was the probing for the auto leveling:

    8:39:12 PMLeadscrew adjustments made: 0.001 -0.001 -0.000 -0.001, points used 4, deviation before 0.001 after 0.000
    8:38:44 PMLeadscrew adjustments made: -0.003 0.003 0.001 -0.001, points used 4, deviation before 0.004 after 0.000
    8:38:16 PMLeadscrew adjustments made: 0.156 0.148 0.154 0.151, points used 4, deviation before 0.153 after 0.000

    Here is the mesh height map:

    0_1540800861805_f6594bd9-10f1-48e2-92be-1a4d2d30121e-image.png

    This was the results from doing auto leveling right after:

    9:14:34 PMLeadscrew adjustments made: -0.000 0.004 -0.002 -0.002, points used 4, deviation before 0.003 after 0.000
    9:14:07 PMLeadscrew adjustments made: -0.001 0.002 0.008 0.003, points used 4, deviation before 0.005 after 0.000
    9:13:39 PMG32
    Leadscrew adjustments made: 0.006 0.019 0.031 0.014, points used 4, deviation before 0.022 after 0.000

    I guess the points do line up other than maybe the second that was 0.01mm out. I am guessing some of the issues I am having could be attributed to the fact that there would be a compounding error over 342 x2 z movements as it probes every point twice?

    Kind Regards,
    Sam



  • Another quick question, do you have to specify a taper at all in the .config or does it default if you do not specify the M376 code? I have not had it in my config file.

    Kind Regards,
    Sam


  • administrators

    If you probe repeatedly in the high-X high-y region (where the error appears to be greatest) using G30 S-1, do you get a consistent trigger height reading?

    The default is that bed compensation is not tapered.



  • Hi @dc42
    Thanks for that. I will give it a go.

    So by not tapering, does that have an effect on the compensation? Or will it compensate over the entire height of the print?

    Regards,
    Sam



  • @samlogan87 said in Mesh Bed Compensation and Bed Leveling:

    Or will it compensate over the entire height of the print?

    Exactly.



  • Hi @Phaedrux

    Thanks for clarifying that. I just seem to have a few issues with consistency between mesh compensation results and auto leveling that I think is causing issues with my first layer being inaccurate.

    Kind Regards,
    Sam



  • For almost any case like this, my first go-to for an explanation would be a machinist's straight edge. 0.1mm deviation over a couple hundred mm is practically impossible to see, but that straightedge should tell the real story. If you are getting incorrect reporting from the sensor, the first step is to determine if your sensor is wrong.

    If your sensor is wrong, then the idea is to determine what rules (And there will be some) that determine HOW it is wrong. Sometimes certain portions of the bed have more compliance than others, particularly when your bed is spring mounted. Sometimes there is a sag or bow in axis rails, and though the bed isn't bent, the probe is correct. this is one of the things that a mesh probe can help correct for.



  • @SupraGuy

    I did one more run last night of the mesh leveling and I want to do another one again tonight to confirm, but some of it could be a slightly bent Y axis (That is my moving carriage axis). I am still getting inconsistency in the mesh leveling which I am not overly sure why, hence the post.

    Kind Regards,

    Sam



  • Well, I did another run and it is not a bent y axis. When I set it up, I had a few good nozzle digs into the bed and I am wondering whether somehow in doing so, it managed to put a slight bow in the center of the bed.

    @dc42 When I run G30 S-1 with the piezo probe, it does not lift after probing and progressively digs harder into the bed. Not sure what I need to change to stop this. Even so at X 340 Y360 according to the mesh height map, the z value should be .197mm. When I probe it is 0.02mm.

    Kind Regards,
    Sam


  • administrators

    You need to raise the head by 5mm between each pair of G30 S-1 commands.



  • Hi @dc42

    I am sure I was doing that. I will have another go at it tonight.

    Kind Regards,
    Sam


 

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