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mesh bed compensation not applying correct corrections

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Tuning and tweaking
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  • undefined
    Phaedrux Moderator
    last edited by 31 Jan 2020, 16:57

    I see you're using the BLTouch. You can attempt to get a bit more accuracy and repeatability out of it by modifying your M558 a bit.

    M558 P9 H5 F60 T6000 A10 R0.75 S0.003 B1

    Slower probe speed, with repeated attempts if 2 consecutive probes don't match to within a tighter tolerance. Probing will take longer because of the slower dive height and it will do at least 2 probes per point. But you will be far less likely to get outliers.

    Z-Bot CoreXY Build | Thingiverse Profile

    undefined 1 Reply Last reply 31 Jan 2020, 17:01 Reply Quote 0
    • undefined
      necrorat @Phaedrux
      last edited by 31 Jan 2020, 17:01

      @Phaedrux so 1 is the rear right of the height map and 3 is the front centre on the height map. sweet thanks for the tip ill change that out and give it a try probably wont be till tomorrow till ill get to try it now though.

      1 Reply Last reply Reply Quote 0
      • undefined
        Veti
        last edited by 31 Jan 2020, 17:14

        can you measure the z trigger heigh at different positions?

        it is possible that you have different trigger heights based on position.

        undefined 1 Reply Last reply 1 Feb 2020, 14:44 Reply Quote 0
        • undefined
          necrorat @Veti
          last edited by 1 Feb 2020, 14:44

          @Veti so i measured the z trigger height and it didn't vary by more than 0.005mm at each of the 9 points i measured at, it did vary from point to point but thats kinda the point of bed levelling isn't it ?

          undefined 1 Reply Last reply 1 Feb 2020, 14:55 Reply Quote 0
          • undefined
            Veti @necrorat
            last edited by 1 Feb 2020, 14:55

            @necrorat said in mesh bed compensation not applying correct corrections:

            so i measured the z trigger height and it didn't vary by more than 0.005mm at each of the 9 points i measured at, it did vary from point to point but thats kinda the point of bed levelling isn't it ?

            no the z trigger height has to be constant across the entire bed otherwise you have the effects that you are seeing.
            to clarify i am not refereing the the result of a G30 but the valude of of Z for G31 when calibrating it.

            undefined 1 Reply Last reply 1 Feb 2020, 15:19 Reply Quote 0
            • undefined
              necrorat @Veti
              last edited by 1 Feb 2020, 15:19

              @Veti just ran though a 3x3 grid to check and i am consistently getting 2.31 for the trigger height

              01/02/2020, 15:16:27 M98 P"0:/macros/probe test"
              Current reading 0, threshold 25, trigger height 2.31, offsets X-29.5 Y11.4

              undefined 1 Reply Last reply 1 Feb 2020, 15:26 Reply Quote 0
              • undefined
                Veti @necrorat
                last edited by Veti 2 Jan 2020, 15:26 1 Feb 2020, 15:26

                @necrorat said in mesh bed compensation not applying correct corrections:

                01/02/2020, 15:16:27 M98 P"0:/macros/probe test"

                does that macro do this?
                https://duet3d.dozuki.com/Wiki/Test_and_calibrate_the_Z_probe#Section_Calibrate_the_Z_probe_trigger_height

                undefined 1 Reply Last reply 1 Feb 2020, 15:33 Reply Quote 0
                • undefined
                  necrorat @Veti
                  last edited by 1 Feb 2020, 15:33

                  @Veti ive wrote it as this to probe 3 times per spot:
                  G1 Z10
                  G30 S-1
                  G1 Z10
                  G30 S-1
                  G1 Z10
                  G30 S-1

                  undefined 1 Reply Last reply 1 Feb 2020, 15:40 Reply Quote 0
                  • undefined
                    necrorat
                    last edited by 1 Feb 2020, 15:38

                    so have just run it again and i am getting quite a large variance now in the region of 0.11mm is this a mechanical issue? the machine is set up on linear rails and i have ensured that they are as square and parallel as possible

                    1 Reply Last reply Reply Quote 0
                    • undefined
                      Veti @necrorat
                      last edited by 1 Feb 2020, 15:40

                      @necrorat said in mesh bed compensation not applying correct corrections:

                      G1 Z10
                      G30 S-1
                      G1 Z10
                      G30 S-1
                      G1 Z10
                      G30 S-1

                      that determines repeatability, but does not determine z probe trigger height as you do not determine z=0 before probing as described in the above linked document

                      undefined 1 Reply Last reply 1 Feb 2020, 15:44 Reply Quote 0
                      • undefined
                        necrorat @Veti
                        last edited by 1 Feb 2020, 15:44

                        @Veti so do i have to go though the full calibration procedure for each point that i probe on the bed?

                        undefined 1 Reply Last reply 1 Feb 2020, 15:45 Reply Quote 0
                        • undefined
                          Veti @necrorat
                          last edited by 1 Feb 2020, 15:45

                          @necrorat
                          do one at the point where the lines where ok and one where the lines where not ok

                          undefined 1 Reply Last reply 1 Feb 2020, 16:09 Reply Quote 0
                          • undefined
                            necrorat @Veti
                            last edited by 1 Feb 2020, 16:09

                            @Veti so just did a test over 5 point and theses are the results :

                            2.064
                            2.068
                            2.066
                            2.059
                            2.046

                            1 Reply Last reply Reply Quote 0
                            • undefined
                              Veti
                              last edited by 1 Feb 2020, 16:53

                              thats a lot different than your original trigger height of 2.31

                              undefined 1 Reply Last reply 1 Feb 2020, 17:16 Reply Quote 0
                              • undefined
                                necrorat @Veti
                                last edited by 1 Feb 2020, 17:16

                                @Veti i have been tinkering with the frame and alignment all day. gonna probe the bed one last time then try another print

                                1 Reply Last reply Reply Quote 0
                                • undefined
                                  Stuffi
                                  last edited by 12 Dec 2020, 12:49

                                  Sry to bring up that old post again.

                                  @necrorat Did you find a solution or the reason why the meshbed compensation didn't apply?

                                  I have the same issue.

                                  1 Reply Last reply Reply Quote 0
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