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Solved Y axis, lost steps?

Discussion in 'Troubleshooting' started by joea, Mar 24, 2020.

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  1. joea

    joea Active Member

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    Trying to print a COVID-19 face mask, as seen at https://longliveyoursmile.com/3d-printable-mask-for-covid-19/

    Seems to be losing steps in Y axis. Not unique to this print. Seems to happen 30 minutes or so into the print. There also was an intermittent noise similar to locked motor, for an instant or two during prints.

    I lowered the acceleration to 600, as suggested in other threads. Actually 300 was suggested, but since I was at 1200 or so, I took a chance.

    This print turned out better, but still, about 30 minutes in (or so as I was not watching closely) I found an offset in the Y axis. I did not notice it to be a noisy, at least at the start.

    I guess I can drop it to 300 and run again, but any suggestions would be helpful.
     
    #1 joea, Mar 24, 2020
  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Tighten the Y belt.
    Check the drive belt cog on the Y motor shaft has the set-screw tight (they can come loose -- loctite is your friend)
     
    #2 mark tomlinson, Mar 24, 2020
  3. joea

    joea Active Member

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    Thanks. I will check both. How tight is "too tight"? For the belt. I know that sinking feeling of a screw/bolt/nut too tight. <g>
     
    #3 joea, Mar 24, 2020
  4. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Sadly I can not give you a strain gauge number :)
    Like the X belts the best answer is "tight enough to make a low thrum when you pluck it"

    That is "thrum" like a stringed instrument (but low frequency) not THUD.
     
    #4 mark tomlinson, Mar 24, 2020
  5. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    The set screw is as tight as you feel comfortable with, it should not be loose.
     
    #5 mark tomlinson, Mar 24, 2020
  6. joea

    joea Active Member

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    I was always told I had a "tin ear". But I get the idea. Whi
     
    #6 joea, Mar 24, 2020
  7. joea

    joea Active Member

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    Removed bed and belt to check pulley. Found that the belt free of the drive and idlers, the travel has a bit of a "hitch in it's git-a-long" sometimes.

    Seems random and related to reversing directions as if the "linear bearings" are sticking here and there. Seems enough to make the stepper skip a beat here and there.

    Known issue? No problem""
     
    #7 joea, Mar 24, 2020
  8. joea

    joea Active Member

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    After cleaning an lubing the rods and finding the screws for one of the linear bearings "not quite snug" and tightening, seems to move much more smoothly.

    Shall see how another test print goes.
     
    #8 joea, Mar 24, 2020
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  9. joea

    joea Active Member

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    Annnd . . . it got worse. So, I loosed the belt. Still bad. Changed the stepper driver. Still bad.

    About to go power up the Big Box when the quiet voice in my head (don't tell anyone) . . . said, check the acceleration settings for something more.

    Whadda ya know. On power off the EEPROM reset to default values. Gotta remember how to fix that.

    So, set them to what sorta worked last time and we shall see.

    30 minutes later, another failure. Outta gas on this one. If no one has a hint? Acceleration values? Bad stepper motor? Bad linear bearings?






































    /
     
    #9 joea, Mar 24, 2020
    Last edited: Mar 24, 2020
  10. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    All possible, but if you cranked the acceleration numbers way down (<1000) and it is still happening then something is loose.
    The drive gear on the shaft, the belt itself or the stepper is loosing steps (which could be a bad stepper or a bad stepper driver)
    The bearings could be the culprit as well, but you should be able to feel them dragging if you manually move the bed.

    If you are certain everything is tight I'd start with a replacement stepper driver (those are cheap)
     
    #10 mark tomlinson, Mar 24, 2020
  11. joea

    joea Active Member

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    Motor shaft tight as I could get it. Put in a new stepper driver as the last step (so far). I just changed configuration.h and uploaded the recomplied code so I don't need to check it anymore.

    If that fails or I keep hearing that "grind" noise, I'll start looking for a new belt and stepper motor, I guess.
     
    #11 joea, Mar 24, 2020
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  12. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Good idea since the grinding noise is the stepper slipping steps. The belt is a standard GT2 timing belt (but I would really be surprised if that is the problem -- I have not seen one fail other than to break).

    Worst case check the alignment of the belt on the drive cog and the idlers in the center is square. I once had the cog slip down on the shaft a wee bit and that made the belt ride and an down in the race on the idler as the bed moved and at some point it would hit the edge of the race and bind. Normally that belt should stay dead-center of the race on the idler as the bed frame moves back and forth. Took me a week to find that :) The solution was simple -- move the cog up on the shaft to where it belonged.
     
    #12 mark tomlinson, Mar 25, 2020
  13. joea

    joea Active Member

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    Frustrating. My favorite word lately.. 3 hours into a print before it did the nasty this time.

    The belt does not seem to be binding. With the belt removed, again, I can find intermittent "rough spots" running the bed support rails through their full travel. Not consistent where this happens.

    Likely to be bad linear bearings? The rods look clean and straight.
     
    #13 joea, Mar 25, 2020
  14. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    That would be the first culprit. It is possible something got out of alignment with the frame/rods/base but certainly the linear bearings they use stock are less than awesome.

    It is only that it would need to be fairly sticky to cause a skip on the GT2 belt (assuming it is tight). Can't hurt to replace those stock bearings.
     
    #14 mark tomlinson, Mar 25, 2020
  15. joea

    joea Active Member

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    Like these? Or Amazon/ebay?

    https://www.partsbuilt.com/linear-bearing-r1-robo/
     
    #15 joea, Mar 25, 2020
  16. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Exactly like those. LM8UU. You can find them on Amazon with MAYBE faster delivery with Prime shipping. Tough call on the last one as Amazon has been delaying non-critical stuff :)
     
    #16 mark tomlinson, Mar 25, 2020
  17. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    That 4-pack will do the Y axis.
     
    #17 mark tomlinson, Mar 25, 2020
  18. joea

    joea Active Member

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    I am failing to see how they install. Captive under the "carrier blocks", just drop out? Also failing to see how the bed rails/shafts come out. Eyeball shows no set screws, etc at either end of the assembly.

    Also, there is a years old thread on replacing with bronze bushings, which no longer seem available. Any point in chasing that idea?
     
    #18 joea, Mar 25, 2020
  19. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Look here this shows most of the assembly:

    https://www.thingiverse.com/thing:681894

    The bearings are inside the blocks that the rods run through.
    You unscrew those blocks (nuts on the back of the mounts IIRC) and pop the tops off and the bearings are seated inside. Remove the rods (which means removing one end of the bed frame the rods form). the bearings are just seated in there, lift them out. Reverse all of that to reassemble.

    If that isn't clear enough this one is an exact match for stock mounts: https://www.thingiverse.com/thing:2854432

    You can see how they are assembled.

    The rods/rails are press-fit into the plastic mounts on the end. You should be able to wiggle them loose.

    This thread has some information on an alternative if you don't want to deal with the bearings: http://community.robo3d.com/index.php?threads/y-axis-bearing-alternative.7167/
     
    #19 mark tomlinson, Mar 25, 2020
    Last edited: Mar 25, 2020
  20. joea

    joea Active Member

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    My current setup only has screws/nuts in the end holes, none in the middle ones. I wonder if that is causing some problem. Easy to find out.

    The last link is what I was referring to about the bronze bushings not being available. Is there some new source?
     
    #20 joea, Mar 25, 2020
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