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Solved Misaligned Print

Discussion in 'Troubleshooting' started by 4sfaloth, Jun 23, 2020.

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  1. 4sfaloth

    4sfaloth Member

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    Hi all,

    In my last print I've noticed heavy misalignments in-between layers. I've attached a picture of it. Some misalignment can be seen in the trunk, but the worst is at top branches where it's a huge mess (but if you look closely you can see heavily misaligned layers).

    I noticed during the print that for some reason it seemed to be printing faster than I'd ever seen it before, in particular in what regards direction changes.

    Most of my prints are significantly smaller than this, and I use a different profile which has much more strict speed and acceleration restrictions.

    1. Do you think limiting accelerations and/or speed will help with this?
    2. Does this also mean that I have a hardware issue (I think belt tension might cause this, right?), or can it just have been bad luck that this particular model made the printer move faster and/or shift directions particularly fast?

    Thanks in advance
     

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  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Probably, this is a classic example of axis drive slip/skip. The speed and acceleration will affect this because with less of both the changes in direction and speed are not as sudden so less force applied to the drive and it will slip/skip less.

    Your last part I already mentioned in the first reply, but I would be certain that you have at least one component loose in the driver for whichever axis is doing the slipping (and it may be both X and Y -- I can't tell from the picture). Things like the belt tension is too loose and the belt is skipping gears. The gear on the motor drive shaft is loose and slipping (there are set screws on those -- tighten them and use loctite). Lastly it could be bad/weak stepper drivers on the RAMPS. Those are what turn the commands from the Arduino into the current that drivers the stepper motor. Too little current and the steppers will miss steps.
     
  3. 4sfaloth

    4sfaloth Member

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    Hi @mark tomlinson , thanks for stepping in once again.

    I've attached a picture of a new print which illustrates the issue even better. You can clearly see a big misalignment in the beginning, and 3-4 smaller ones nearer the top.

    It seems to me that it's the Y axis slipping.

    From your post I believe you mentioned three different possible causes for this:
    1. Loose belt
    2. Loose/slipping gear on the motor drive
    3. Bad/weak stepper drivers on the RAMPS
    is there any way I can distinguish in-between these possibilities? I really did not want to start messing with any of those without being sure there's a problem with them

    I'm a bit concerned with the third possibility, because I do think the printer is making a weird crackling noise which sounds electronical in nature and I'm pretty sure it didn't do that before (at least not so loud). I tried to record the noise in a video but I'm not sure if it's very clear what I mean: https://imgur.com/a/SFwNn2F

    Besides the above I'd like to pose two more questions if you may:
    A) As you can see I am using a second glass bed clipped to the original ones using some binder clips. I've been doing this for over a year without any issues I think. Do you think it's possible that top bed is slipping with respect with the other one?
    B) This print (as well as many others before) was performed with a Raspberry Pi controlling the printer. The PI is running a tool called octoprint which basically allows it to control the printer, as well as providing live feed via a WebCam and making timelapses etc... If the PI is overburdened (for example because the camera has too high resolution and/or frame rate) is it possible that could make these symptoms on the print?

    In the meantime I will try another print with reduced speed/accelerations.

    Thanks once again
     

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  4. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    I agree now that I can see it :) The Y is slipping.
    Loose belt is easy to check, just tighten the adjustment screw for it (it is on one end of the rail under bed) there is a screw you can adjust to tighten the belt. Lift the bed while while doing it and you can watch the belt and see it get tension.
    You can (with the bed lifted) check the sprocket on the Y motor shaft and see if you can turn the sprocket on the shaft while holding the shaft in place. If it moves at all then that is bad -- check the set screws.
    The last thing to check is the stepper driver chips and honestly as cheap as they are (from Amazon for example they are <$2 each*) I would just swap the Y axis stepper driver with a new one -- OR as a test swap it with the X driver and see if the problem moves to the X axis :)

    I can't really make out the sound you are referring to but if the stepper motor is dropping steps (which could happen if the stepper driver for one axis is getting weak/tired then it will make a grinding noise each time it drops a step.




    *one example: https://smile.amazon.com/HiLetgo-Stepstick-Stepper-Printer-Compatible/dp/B07BND65C8 just search for A4988 and you will find a number of sellers.

    No, I doubt that would have this effect, but if it does you should be able to make some alignment marks on the glass bed / bed frame and then check them after a failure to see if it has shifted any. Maybe use a grease pencil or a magic marker...

    Nope (and that is the very setup I use myself on almost all of my 3d printers).
    If the pi were slowing things down the Arduino board on the printer would simply print slower :) with perhaps small pauses.
    It would not cause a print defect like that.
     
  5. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    If you have been printing a long enough time and never had to adjust any of the belts or cogs then that is most likely the issue. Something just got mechanically loose. I need to periodically check all of mine as well (which is why I really do suggest loctite on the screws). The belts can stretch, but the GT2 timing belts they use are pretty robust and take a long time to do any stretching
     
  6. 4sfaloth

    4sfaloth Member

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    not sure what you "long enough time" would be :)
    I've had the printer for almost 2 years now, and never made any adjustments to the belts/screws.
    As for use rough estimate is about 7.5Kg of filament and 760h of printing (this does not include misprints etc...; also it is based on slicing time which are sometimes underestimated, so the real value is most likely a bit larger).

    In the meantime I've printed a few more minis with the acceleration restrictions and they all come pretty well with no misalignments. So I guess the issue is not yet pretty bad, and only reveals itself in faster prints. I'll continue printing slowly until I can take a couple of hours to make the recommended adjustments.

    I don't think I'll replace the motor drivers for now; they are cheap alright, but I really do not like to open up the entire printer and mess with the electronics :p
    If this continues to happen after the mechanical adjustments I'll consider it then

    Thanks for all the help
     
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  7. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    For your usage, that is a bit long. Probably once a year would be good for checking everything,
     
  8. 4sfaloth

    4sfaloth Member

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    Alright I believe it's done.
    Just to make sure, you're talking about the screws signaled in the attached picture, right?
    Only the only signalled in red seemed to be attached to the belt, but I suppose that's normal?
     

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  9. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Yes, one of those screws has the belt attached on the other side. Lift the magnetic bed a little so you can look under it and you will see which one has the belt. The adjustment screw is at one of the rail ends.
     
  10. 4sfaloth

    4sfaloth Member

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    yeah, that's what I did. Ok thanks :)
     
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