SOLVED - Help me solve some Z Banding

mrehorstdmd

Try removing the wheels from the back corners. 4 wheels is an over constraint condition, liable to cause the bed to walk as it moves up and down. You really should only need the wheels at the corners closest to the leads screws that are on the right and left side in your first photo.

Phaedrux

@mrehorstdmd I'll give it a shot.

wilriker

@mrehorstdmd said in Help me solve some Z Banding:

Try removing the wheels from the back corners. 4 wheels is an over constraint condition, liable to cause the bed to walk as it moves up and down. You really should only need the wheels at the corners closest to the leads screws that are on the right and left side in your first photo.

Just to check if that was not lost in translation for me (and @Phaedrux already understood what you said anyway) and I am curious: are you proposing that on the backside the bed will only be "held up" by the leadscrew and otherwise kind of cantilevered mount only on the front side where the two leadscrews are?

deckingman

@wilriker said in Help me solve some Z Banding:

@mrehorstdmd said in Help me solve some Z Banding:

Try removing the wheels from the back corners. 4 wheels is an over constraint condition, liable to cause the bed to walk as it moves up and down. You really should only need the wheels at the corners closest to the leads screws that are on the right and left side in your first photo.

Just to check if that was not lost in translation for me (and @Phaedrux already understood what you said anyway) and I am curious: are you proposing that on the backside the bed will only be "held up" by the leadscrew and otherwise kind of cantilevered mount only on the front side where the two leadscrews are?

No I don;t think that is what is being proposed. The bed will be held up by all three screws and 3 point define a plane, so it will stay level. If I understand correctly, Mark is saying (correctly in my opinion) that you only need 2 linear guides to constrain any side to side movement. 4 is overkill and there is a risk of binding if they aren't all perfectly aligned.

deckingman

@phaedrux Given the problems you've had in the past with your OpenBuild wheels, are they all free to rotate? No flats like you've had in the past? Not over tightened the eccentric spacers by any chance?

mrehorstdmd

@wilriker yes, like a cantilever with an extra screw to hold up the free, bouncy edge.

Phaedrux

@deckingman said in Help me solve some Z Banding:

@phaedrux Given the problems you've had in the past with your OpenBuild wheels, are they all free to rotate? No flats like you've had in the past? Not over tightened the eccentric spacers by any chance?

That's the first thing I checked. Some of the Z axis wheel bearings were indeed failing and leaking lubricant similar to the ones I found on the X and Y axis. However even after switching them back to working delrin wheels and bearings there was no difference.

I should also make clear that the polycarbonate and delrin V slot wheels were not OpenBuilds. They are from Xinlong Factory on AliExpress. I have some OpenBuilds V wheel bearings on the way though. Even with the bad bearings the movement was smooth by hand.

@mrehorstdmd I understand the overconstraint situation, but with everything aligned and properly tensioned the motion is very smooth and low friction. But I will definitely give the 2 wheel solution a try later today.

Thanks for the feedback.

mrehorstdmd

It only takes a few 10s of um of error to create a visible defect in the print, which is why chasing this sort of problem is so difficult. You can't see what's causes the defect, so you have to use your imagination, test and test and test until you find/fix the problem.

Phaedrux

@mrehorstdmd Well I got a chance to remove the back wheels and test again. No difference.

My replacement pulleys, belt, pillow blocks and bearings have arrived though, so I'll see if that helps at all. Unfortunately the pillow blocks I received KFL08 and KP08 have very poorly inserted bearings. I've tried tapping them straight but it seems to be a losing battle. So I think I'll stick to the printed bearing blocks for now.

Now I'm thinking that I should have just ordered some replacement lead screws as well and just change everything out at once, rather than do all the disassembly and assembly again if this doesn't work. I was foolish and wanted to save $22.

Phaedrux

The openbuilds pulleys measure almost perfectly round to within 0.01mm. That's far better than the pulleys I had before, so that's promising. The 1534mm continuous loop GT2 belt from openbuilds seems to be of better quality as well. The previous belt seemed to have a bit of an odd cut angle to it. The new one has a flat cut edge and the teeth seem more pronounced. It also has the same texture and appearance to the genuine Gates belts I have. Though they don't have a stamp to indicate they are actually Gates belts. The new bearings are also higher quality. Completely silent and smooth and just feel more solid.

Really hoping this does it.

Phaedrux

I fixed it!! It took a better part of the day to tear it down and build it back up but at least now I can print without being ashamed of the quality.

Left is before, right is after. Same gcode.

I did a complete realignment of the bearing blocks and bed mounts to make sure they were lined up. I also tightened up the V wheel tensioners on all 4 corners and ensured that the bed raised and lowered smoothly and evenly by hand. Plus I replaced the 40T lead screw and drive pulleys with new ones from OpenBuilds. This time using a 20T drive pulley giving me a 2:1 gear ratio. The belt was also replaced. The cheap toothless flanged idler pulleys on the belt tensioner were replaced with flanged 605 bearings which ran much smoother and didn't rub the belt like the old idler did.

I don't know if it was just one or all of those things, but the banding is completely gone. I suspect that the biggest issue was the pulleys. There was visible wobble and movement with the old ones. That's all gone now. It's hard to put a finger on it, but visually the quality of the belt movement just looks better than before.

Thanks everyone for the suggestions.