Automatic calibcration results - is it as bad as it looks?!

  • I added a 5mm aluminum plate to my printer today and did the G29. The result looks like this:

    Is it as bad as it looks or is just the back left a tad too high? And why is it so far above the 'bottom' of the graph?

  • if the entire bed is above the z = 0 on the graph then it means your z=0 is wrong,
    try doing a G30 first to set the zero correctly then it should bring the whole plane down

  • My G31 looks like this

    G31 T1 P500 X10.0 Y-44.0 Z1.85

    and I got the 1.85 from the procedure of how to set up the dc42 probe (paper, G92 Z0, …). Do I have to set anything else?

  • administrators

    It looks as though after you home Z, Z=0 doesn't correspond to just touching the bed.

  • My 'Z-Home' is at X100Y100 (because the probe is not over the bed at X0Y0) - can this be the problem? Should I home at X0Y25, where the probe is just over the bed?
    After homing (at X100Y100) and going down to Z0 the gap is the same as I set it up (same drag on the paper) 😕

  • I changed my homing position to X0Y25 and also (after measuring again) altered the Y offset of the probe in G31. Then I did the papersheet-calibration for the new homing position wich got me a trigger height of 1.68, then doing G29 I got a lot of green and the back left is a bit higher, wich is kind of right. But now the height in the center of the bed while printing does not seem to be correct, the first layer is not at the correct height. I'll try tuning the trigger height and see what happens…

  • administrators

    I recommend probing for Z homing at or near the centre of the bed, unless there is a good reason to do otherwise.

  • So I reset the changes, now homing again at X100Y100. After calibrating I get this height map:

    This looks better…

  • This looks really cool! Ordering a Z probe and a new controller card first thing in 2017 😄

  • FYI darookee,
    frustratingly, I'm getting nearly the identical results you've posted the graph of above when I used my mini IR probe atop thin PEI sheet painted on underside with bbq paint, all atop 4mm Boro glass. I recently received a BLtouch in the mail and after reviewing their claim to accuracy, I finally mounted it up very close to my effector center and tried again, figuring the variation (like your graph) must've been due to sought variations in the mini IR sensor readings due to non uniformity of possibly the thickness of painted underside. The results are so much worse in the case of the BLtouch, which is not only surprising but frustrating as well. I'm not sure what it takes to get a good level result but I'm beginning to get irritated with the whole process considering the trial with the new BLtouch sensor should be miraculous because it's probing very classy glass with nearly perfect uniformity but still I can't seem to get a constant, not to mention acceptable result.

    Any thoughts would be greatly appreciated by anytime reading this thread.

    Thanks, in advance,


  • administrators

    For anyone getting inconsistent results with any sort of Z probe on a delta, I suggest the following tests:

    1. Position the nozzle about 5mm above the bed, run G30 S-1 to probe, then read off the Z height. Send G1 Z5 and repeat. Do this several times to see how reproducible the trigger height is. At a constant XY position, you are looking for it to be reproducible to within about 2 microsteps at x16 microstepping. That's normally 20 or 25 microns if you are using 1.8deg motors, or half that if you are using 0.9deg motors. I use the IR sensor on PEI and I get consistent trigger height to within 10 microns.

    If the trigger height is less consistent than that, try a lower probing speed (F parameter in the M558 command). If it still isn't consistent, check whether you have too much friction in your carriage movement and reduce it if necessary. Higher motor current may also help. If that's not the problem, then it's probably down to your Z probe.

    2. If that test gives a consistent trigger height, try a similar test but move the nozzle to a different XY position and back again before the G30 S-1 command. If the trigger height becomes inconsistent, suspect play or friction in the joints.

    HTH David

  • Thanks for the tip toward troubleshooting these issues. I'll let you know how my progress goes (hopefully it will get better since hearing this tip)

    Jonathan l

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