Z axis banding worse at top.

Discussion in 'Calibration, Help, and Troubleshooting' started by moshen, Jul 14, 2016.

  1. moshen

    moshen Well-Known Member

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    Finished building my preorder BigBox 1.1 and have been trying to tune out some z-banding. In my test cylinder I have the light to highlight the surface quality. Near the bottom the quality is good and gets progressively worse near the top. You can also feel this by hand, so it's not from how the lighting is. I was pretty careful during the comissioning to make sure nothing was binding.

    Anyone have suggestions on what to check? Thanks!
     

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  2. PsyVision

    PsyVision Moderator
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    Put the bed all the way to the top and then move it all the way to the bottom (move in 3x 100 chunks for example) and watch the top of the couplers between Z-motors and leadscrews. Check to see if they stay absolutely level or whether they move around.

    Mine weren't that well tram and caused extra banding.
     
  3. moshen

    moshen Well-Known Member

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    They seem ok to me, but I'll check again to make sure. What did you do to fix that, just loosen and screw back in again?
     
  4. PsyVision

    PsyVision Moderator
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    Yes basically.

    The other thing I did was to put a bearing in the plate at the top of the leadscrew to hold it in place whilst doing the adjustments. This helped to keep it central. I then removed it afterwards.
     
  5. moshen

    moshen Well-Known Member

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    I've re-commisioned everything and reseated things many times. The bed slides smoothly on the rods. Still have issues with banding at the top of the print. Really pulling my hair out over this. Since it mainly happens near the top this makes me think it's something with the motor/coupler connection when it is printing high. The z wall is perfect at the bottom of the print and when the bed is up high where the lead screw can move freely on the horizontal plane. When the bed is near the bottom it gets more constrained.

    I've ordered two plum couplers. It will take a few weeks to arrive and we'll see how it helps.

    If you print a 280mm high 25cm diameter cylinder in spiral mode do you consistent walls all the way along the length of the print?
     
  6. PsyVision

    PsyVision Moderator
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    I got my BB just before Xmas and spent days printing prints like this for the exact same reason... Google+ has the evidence. It prints good now yes. My problem was the couplers as described earlier. I did buy some plum couplers at the time but never tried them.
     
  7. moshen

    moshen Well-Known Member

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    Well so far I have disassembled and recomissioned all the rods, couplers, motors many times. Trying to get things as parallel as possible, looking for wobbling, etc and still no progress at all. Layers are perfect the first 4 inches then the banding starts getting progressively worse. Still points to the coupler/motor being the issue with it getting progressively worse when the bed is at the bottom but I just can't figure out where the misalignment is. My Printrbot Simple Metal is printing much better at this point. So frustrating.
     
  8. moshen

    moshen Well-Known Member

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    Can someone else try printing this test tower (1cmx28cm) attached and upload a photo with it lit like I have (to show ridges). Print only one wall thick and it should take 30 minutes at 40mm/s. I've tweaked and reseated for hours and no matter what I do the walls are perfectly smooth for the first few inches then progressively gets worse. I'd just like to see that a well tuned BigBox can actually do this test well .. consistent walls top to bottom. Thanks!
     

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  9. mike01hu

    mike01hu Well-Known Member

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    g
    In my opinion, that part is too long and too small in cross section to achieve stability over the length. As the print gets higher, filament drag from the nozzle will pull the piece and cause the distortion you are seeing. You should increase the cross section and use infill to provide lateral stiffness.
     
  10. moshen

    moshen Well-Known Member

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    You were right on that particular part. Instead I printed the 30cm cylinder again, with three layers and some cross section infill to make it stiff. Unfortunately I still get the progressively worse wobble as the print gets higher. I also tried two different couplers, a non helical and now I have a plum coupler installed. Still the same issue.

    My theory is the bed is wobbling and as the bed gets lower, the angle of wobble from the print head gets magnified. Thus it starts off great and gets worse. My bed runs very smooth so it could just be the play in the bearings (which are upgraded Misumus).

    Can someone try printing a 30cm cylinder in spiral mode and see if they get consistent walls top to bottom? The quality of the wall is great for the first few inches and I'd like to have that be consistent. I'm just wondering if this is fixable or just the limitation of the design. My Printrbot Simple Metal can only print 6" cube, but it uses two 12mm thick z rods and two spread out bearings on each rod. So rods are thicker and the supported bearing length is longer - leading to superb z walls over the entire height. It's possible the four 8mm rods and much smaller supported length with one bearing on each rod may not be enough for such a tall build volume?
     
    #10 moshen, Jul 24, 2016
    Last edited: Jul 24, 2016

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