Installed New Z-rods and Brass Nuts; Looking better now

Discussion in 'Calibration, Help, and Troubleshooting' started by JvdP, Mar 27, 2016.

  1. JvdP

    JvdP Well-Known Member

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    I'm one of the early backers so I had some trouble with my banding on my Z axis earlier.

    IMG_5083.JPG

    As you all know, the guys over at BigBox have shipped new parts to everybody that had this problem. This included new Brass nuts, new smooth rods and also some new printed parts to change the way the rods were mounted.

    I've had these parts lying around for a few weeks now and finally got the time to install them. I quickly did a Ø30mm hollow cylinder to test.

    IMG_0163.JPG

    As you can see, most problems are gone. However at the top (starting from about 235mm) you can see some banding occurring. I'm not even sure it's banding, it's just, uneven.

    IMG_0169.JPG

    IMG_0172.JPG

    What do you guys think of this? Is this comparable to your BigBoxes? Should I do more tuning? I'm considering loosening and tightening again the Couplers.
     
  2. Mike Kelly

    Mike Kelly Volunteer

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    Yeah adjust the Z threaded rods a bit so they move very straight and smooth with minimal to no wobble.
     
  3. mike01hu

    mike01hu Well-Known Member

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    It is repetitive, so I would suspect you already have the solution.
     
  4. R Design

    R Design Well-Known Member

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    I printed a 1cm diameter cylinder as a test.

    Towards the top it was clear that it was wobbling!
     
  5. JvdP

    JvdP Well-Known Member

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  6. Spoon Unit

    Spoon Unit Well-Known Member

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    @JvdP I'm running your test now. A Ø30mm cylinder, 280mm high. Running this test on the right-side extruder with the 0.6 volcano using E3D Everyday PLA.

    Too early to say, but so far so good.

    2016-03-28 22.52.42.jpg
     
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  7. Spoon Unit

    Spoon Unit Well-Known Member

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    @JvdP my print looks pretty solid

    2016-03-29 08.05.36.jpg 2016-03-29 08.05.45.jpg 2016-03-29 08.05.55.jpg 2016-03-29 08.10.09.jpg 2016-03-29 08.11.48.jpg 2016-03-29 08.10.56.jpg 2016-03-29 08.10.43.jpg

    The feel test says that there are some small variations end to end, but moving my hand around the cylinder at all points along the length it feels smooth.

    There's a clear couple of lines all the way from top to bottom at the front center and right center. Though they're really incredibly tiny, they do show up as you twist it and view the reflected light. I'm guessing they are backlash marks.
     
  8. mike01hu

    mike01hu Well-Known Member

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    It does look pretty good!
     
  9. JvdP

    JvdP Well-Known Member

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    @Spoon Unit So, I have looked at your tube (...haha) and it looks REALLY good. I'm positive that yours is better than mine.

    I've checked my threaded rods and the left one seems to be quite solid, it doesn't wobble. However the right one wobbles around 1mm. Do your threaded rods wobble? This could be part of the problem.

    Edit. By the way, I really, really appreciate that you went through the trouble to print this tryout for me! Best 3DPrinter community ever.
     
  10. Spoon Unit

    Spoon Unit Well-Known Member

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    Yep. My threads wobble a lot actually. There's two wobbles really. The first wobble is the wobble of the rod connector at the bottom. I guess this is somehow not fully square on to both the top and the bottom. Perhaps something I could look at resetting . In theory the bottom should be solid, and the top could be pulled up slightly more on one side than the other (maybe?) but then again that's a pretty solid thing so must be the bottom. The second wobble is the wobble on the threaded rods, but this only occurs when the bed is quite low. In this case, the top of the rod is unsupported anyway so it makes sense there's some level of wobble there. The bed should be hold in place though by the positions of the vertical corner rods.

    Any XY problems should really exhibit at all Z, so it seems you do have a Z issue somewhere. It feels like the problem they set out to fix is still somehow present for you when the bed is at the bottom. Perhaps you should unscrew the base and caps for the vertical corner rods and go back through commissioning for those. I can imagine that if they're not aligned well, they could rub more than they should as the bed gets lower.

    No worries for running the print. It's a great test case anyway and it provided me with a way to test the full Z range on mine for the first time so, it was due. Great that it could serve two purposes. Might be interesting to print one in each corner too.
     
  11. JvdP

    JvdP Well-Known Member

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    I'm surprised to hear your rods wobble as much as you describe. I was expecting them to not wobble at all. If you are considering "fixing" your wobble, DON'T! From what I can tell from your photos is that yours is about as perfect as you can get it and obviously the wobble isn't playing a big role.

    Although I agree with your theory that the smooth rods are supposed to garuantee X/Y stability, in practice the movement (wobble) of the threaded rod will effect the bed due to bearing clearance and flex. I suppose this will be different from printer to printer...

    I might be a little picky here on these Z-artifacts, but honestly I'm expecting more from the BigBox. I have a cheap H-bot style printer that is falling to bits lately, but it has given me better quality prints than the BigBox albeit the latter being 3 times the price... To me this is a great example where 4 smooth rods (more constraining) does not necessarily have to be better than 2 smooth rods.

    After my last rebuild I'm confident that everything is right because I did everything according to the wiki, according to my experience as well as according to the rules of engineering. Everything checked out and seemed right.

    I want to spend the little time that I have printing, not fault seeking and fixing the Z, especially not after E3D BigBox has claimed that it's all fixed. I struggle to see the point of simply dismantling and rebuilding the Z. I'd like to take a little more direct problem solving approach.

    At this stage my best guess is that there's something with the LM8LUU as the bed was still not moving 100% smooth when moving it slowly by hand. I will order new ones from a source I know is good (Misumi) and install these when I get the time.
     
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  12. Steve1334

    Steve1334 Member

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  13. moshen

    moshen Well-Known Member

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    Did you ever fix your issue? I am having the exact same problem with the banding/wobbling appearing at the top of the print (or when the bed is near the bottom). Have tried everything, and realigned things many times as best I can.

     

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