Bed Tilting?

Discussion in 'Motion System' started by Killercds, Nov 16, 2019.

  1. Killercds

    Killercds Member

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    Had an issue earlier where I tried running the mesh compensation script and it showed up going from -0.25mm on one side to 0.25mm on the other.
    After a bit of investigation, it seemed that the bolts attaching the bed assembly to the linear rail were loose.
    I was able to tighten things up and get things back within an expected range, but had to use the Torx security bits from my iFixIt kit...

    Just curious if anyone else had encountered issues, and wanted to post in case somebody couldn't figure out why a regular hex-head wasn't working
     
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  2. Greg Holloway

    Greg Holloway Administrator
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    I will be changing the assembly docs to make sure this doesn't happen again. This is the second report of these screws being loose.
     
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  3. Jai Stanley

    Jai Stanley Well-Known Member

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    I have a similar issue: One of the bolts that hold the Z axis bed frame to the machined sub-assembly is seized. I use good quality Bacho allen keys, and one slipped and rounded in it. The slack in the heads of the bolts is very surprising: almost like they are imperial, not metric. Quite why button heads and not cap-heads were used here is beyond me.

    I have however levelled the bed using aluminium foil shims under the aluminium bed support/frame interface. Each shim is cut with scissors, measuring 0.02mm each. Using the mesh bed level sequence and display I managed to iteratively improve the bed level immensely. Also: none of the glass beds or my own polycarbonate beds are flat when hot or cold. Thus, however flat/level your bed is, leave mesh bed levelling on!
     
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  4. 1013D

    1013D Active Member

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    I had the bolts extremely loose on mine too. practically 5mm gaps, but the screws were tight. Either the wrong length screws were used, or the threads in the rail trolley thing were not tapped all the way (or the counterbores in the machined part were too deep).....Simple enough fix, replaced with shorter screws (still plenty of thread).

    Also, The motor pulleys in the motion system were completely missing set screws. Found this when trying to first home the machine. luckily I had some on hand.
     
  5. garethky

    garethky Well-Known Member

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    I also discovered this the hard way.
     
  6. Nibbels

    Nibbels Well-Known Member

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    Same here.
    It was the screws torque between the thick milled aluminium H-looking part and the linear rail.
     
  7. Michael Pearson

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    These bolts were loose on my TC that I just got last week. I had near perfect level after assembly and suddenly switched to +.25 / -.21. On investigation I found the same that the bolts to the carriage were slightly loose allowing the bed frame to rock side to side. I tightened them up and all is well. Excellent Machine!!! Beautiful Engineering!! Cannot express enough how awesome this machine is and I've only begun to tinker.
     
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  8. Greg Holloway

    Greg Holloway Administrator
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    Glad you like it :)
     
  9. Spoon Unit

    Spoon Unit Well-Known Member

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    Have had to tighten mine too. If you accidentally move the machine beyond its limits - particularly at max Z - this will also tilt the bed and the only fix will be to loosen those screws, level, and re-tighten; so I'd guard against threadlocking those screws. I appreciate that the system should never move past Max Z, but it's very easy to generate this outcome; print something as tall as you can, turn the machine off and on, then run the homing process - this will instantly wreck your alignment and have you panicking wonder how to move the bed up without being homed. I'm not sure what the best guard against this is, but I'm tempted to have the machine move Z to 150 at the end of a print as a precaution to prevent this. I wonder if anyone else did something similar, had a similar issue, or adopted a protocol to prevent this happening to their machine?
     
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  10. bcprint3d

    bcprint3d Member

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    In this case, I would use M564 to allow me to manually move the bed up to a safe location.
     
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  11. Spoon Unit

    Spoon Unit Well-Known Member

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    You could do that if you noticed it. But if you weren't expecting the issue in the first place, you end up with the problem specified. It's also possible to use G0 with an H parameter to drive the machine to safety manually should you need to move it. But in the case where the machine was turned off at a position that's unsafe to move Z a set amount, there's no simple automated way to remedy the situation. Therefore you ideally need to ensure the problem can not happen. Another guard would be to add an end stop down there. In any case, M564 is a new one on me, so that's good to learn about.
     
  12. bcprint3d

    bcprint3d Member

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    I hear what you are saying. I built another printer that had the same kind of issue. I have just become used to keeping an eye out for that situation. An endstop at the bottom of the z axis may be worth the effort though.
     

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