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Unresolved Print dimensions off.

Discussion in 'Troubleshooting' started by joea, Nov 20, 2019.

  1. joea

    joea Member

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    Printed the leadscrew adapter https://www.thingiverse.com/thing:1147438 as a test.

    The Z axis dimension came out pretty much spot on, which was a pleasant thing.

    Oddly, X came out as expected, but Y was short by about .022 inches. The hex "nut" part came out a bit off as well, indicating X was fine, but Y was short.

    Since I am certain my X and Y steps/mm are correct I wonder what the problem is?

    I know about the jumpers for steps on the control board at least in theory. IF I read the information correctly, the jumpers appear to be the same for both. I'm not sure any difference in jumpers would result in that small an error in any case.

    I do, occasionally, while printing hear what I might term "stepper stress" that I think I recall from years past as trying to step "too fast" or accellerate "too fast" under some conditions. However, if it lost steps, I would expect the print to be "offset" from there as the print progressed.

    Sigh.
     
  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    It can only be :
    1) Control (Arduino and firmware) incorrect
    2) Electronics faulty (RAMPS or stepper drivers or stepper motors -- one of them dropping steps)

    If you have isolated it to the Y I'd replace the Y stepper driver with a new one and see what you see.
     
  3. joea

    joea Member

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    I'll give that a try.
     
  4. joea

    joea Member

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    Is there a part number or other identification for the stepper driver?
     
  5. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    They look like this :)

    https://smile.amazon.com/gp/product/B00MQR93QC

    Search Amazon for A4988 stepper driver and you will have many choices.

    (and as you can tell they are horrendously expensive -- which is why I suggested starting there)
     
  6. joea

    joea Member

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    Thanks.

    Have you used these specific ones, or just pointing to the type? I guess I also need to look for the "adjustment procedure" that is referred to in some reviews.
     
  7. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    I used those specific ones as well as a handful of others. As long as they are using the Pololu chips they will all work about the same.

    The adjustment procedure is to make sure that:

    1) You are sending enough current to the stepper to NOT drop steps
    2) You are not sending more current than needed for full steps because that causes the stepper to overheat

    Me personally? These come pre-set and I just use them as-is and if one starts showing issues I throw it out and use a new one. They are so cheap it is not worth my time to spend much fiddling with them. However, it is worth learning how to do it so that you more fully understand the system (if for no other reason) :)

    https://www.pololu.com/blog/484/vid...limit-on-pololu-stepper-motor-driver-carriers

    P.S. if the steppers are running a bit hot, heatsinks are available from Amazon that you can slap on them to assist in cooling them down. I used that approach on our Delta because it really did need to push more current to the steppers (6 foot worth of travel on the axis)
     
  8. joea

    joea Member

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    I'll turn on captioning and give that link a good look a bit later on. Also found a post, here somewhere, about methods of adjustment. May just try the "by ear" method (my term).

    I did put the dial indicator on the bed and it seems to move and return, in 1mm increments at least, just as it should. Certainly not proof it is perfect under the stress of constant running.

    Gave some thought to swapping the drivers around, but that is probably not really going to prove anything. Also gave some thought to tweaking the Y driver to max but paused. I suppose that can hurt nothing for a 25 minute print. To monitor motor temp I would have to rig up a monitor of some kind, or put the printer on a raised platform and monitor by feel. The potential for "shock and awe" notwithstanding. Hmm, I do have a IR "gun" thermometer around here somewhere.

    By "steppers running hot", do you mean the drivers or the motors? If drivers, are there better heat sinks from those supplied?
     
  9. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    I meant the motors get hot. The stepper drivers have heat sinks but with or without them they self-limit the current based on the heat they are "feeling" :) Without heat sinks on the drivers they will run at about 1 amp and with heat sinks closer to 2 amp.

    If the stepper motors are to hot to lay your hand on comfortably, then they need heat sinks or to drop the current.
    Here are some sinks that work: https://smile.amazon.com/BNTECHGO-Aluminum-Heatsink-Cooling-Silicone/dp/B01HSBM72W

    Same style I used on my delta (I even put TWO on each stepper with that one).
     
  10. joea

    joea Member

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    They appear to mount on the sides of the motors?

    So, to my thought of tweaking the existing Y driver and testing that way?
     
  11. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Yes, they mount to the side or rear of the stepper motors themselves.
    Sure, you can try tweaking the current up on the Y driver (that video I linked has instructions)
    It has been my experience so far that once I need to tweak the current output on a driver to push more current -- I will soon be replacing that driver*. Just FYI :)


    *Your mileage may vary, void where prohibited by law, etc
    just stating my experience.
     
  12. joea

    joea Member

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    While waiting for Amazon to ship the drivers (and stop trying to get me to go Prime), I was poking about and noticed the Y Drive belt seems to be rubbing on the upper "guide" of the drive motor pulley.

    There seems to be plenty of space on the lower (motor) side of the pulley, suggesting a slight mis alignment of that pulley as the belt appears to run centered on each of the idler bearing thingies. However to the extreme of motion it appear to ride up on the rear one as it nears the rear attachment point.

    I guess the simple question is, could this be contributing to my dimensional difficulties and what is the proper way to get at the pulley set screws to adjust the distance. Hoping not to have to remove the bed.
     
  13. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Yes, it could contribute by increasing the required motor drive current :)

    Post a picture of the problem is we can get a perfect idea of where you are looking.
    If the picture can't be scaled down, use imagur or flickr to host it and post a link
     
  14. joea

    joea Member

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    View from front. Motor pulley is center, front idler to left. The set screws may be accessible via a cutout in the base.


    20191125_140933 (Small).jpg
     
  15. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    OK, this used to be in the FAQ :)
    What has probably happened is that the gear on the Y stepper that pushes/pulls the belt has slid down on the stepper shaft and when that happens (since the alignment is no longer centered for the belt) it will ride up/down in the race for the pulley(s) and rub causing issues like you describe.

    Remove the bed (magnets should let you pop it free) and watch the belt as you move the bed back and forth. Should be an easy fix. The drive cogs (and pulleys for that matter) have set screws that hold them in place on the shafts. Those can get lose over time (I suggest loctite when you reassemble)
     
  16. joea

    joea Member

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    Do I need to be concerned about wires, heater, sensor, etc when removing the bed?

    I did manage to get the set screws loose and move the pulley, but it's turning out to be problem trying to tighten them.
     
  17. joea

    joea Member

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    Well, that was a lot easier than I feared. Test print may tell something, later on.
     
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  18. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    As I think you already found out -- no :) Just be careful and you will be fine.
     
  19. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    It can be fussy trying to get to the set screws among the belts :)
     
  20. joea

    joea Member

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    Not so easy after all. Turns out, I could not get the set screws tight enough. They would not bear on the shaft. Seems the pulley was on upside down, I guess since forever.

    Took me a while to clean up the pulley bore so it would fit on the shaft. Had to completely release the belt to get they pulley off and on. I figured the belt tension was no big deal, and did it by feel.

    Since then I've not been able to get a good print with the calibration circle. And now, got a printer shutdown, with hardware-error.PNG

    The extruder fans appeared to be running when I caught this error.
     

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