Have you ever checked the bearings that are on the 2 thicker rods on the back?
Maybe there is something going on with those, (or one of them).
I can remember that the bearings on those rods need some time to stop sounding as if there's sand in them. Some sewing machine oil might help on the two silver shafts.
On my heated bed kit that is.
Edited by GuestIt's most probably the sound of the linear bearings at the 2 sides of the z screw. There's no fix, they have toons of balls and they self lubricate. It won't affect the quality since they are linear. Some make more sounds than other in my 3 printers umo+.
Those are ball bearings falling as neotko mentions. It's fine. However you want to grease the screw but not the linear bearings. And no oil is needed. If you have horizontal banding where you have underextruded layers it might not be the Z stage but just typical underextrusion. But if you have *overextruded* layers alternating with possibly underextruded then indeed you probably have Z bearing issues.
please post a photo of a part you printed with "banding" to distinguish.
The fix for the Z bearing banding issues is to take them off your plate and clean them out thoroughly getting all oil and grease out. Oil can actually jam up the bearings a bit. But I'm not 100% convinced that's your banding problem.
Sorry for the long delay, but thank you everyone for the replies. I'm convinced the linear bearings were an issue. FBRC8 was great and shipped out replacements fast.
[media=8839]This is a sample of the banding I was seeing[/media]
Then I dismantled the rods and linear bearings and discovered a good bit of static friction needed to be overcome before the beaings would slide down the rods. Once the bearings were rolling they'd keep rolling pretty well, but getting them started took too much pressure I thought. So I soaked the bearings in parts-cleaning solution, let them dry completeley, bathed them in sewing machine oil, packed them with grease by filling the cylinders with grease and forcing the rods in from each side of the cylinder, and cleaned off the excess. Now only a little pressure was needed to start the bearings rolling.
I reassembled the machine and printed some new parts, and the layers were much more even. I don't have any "after" shots with me and I'm overseas, but I'll shoot some when I get home in a couple weeks.
Maybe grease is a bad choice long term because it may gum up and cause sticking again, but for short term things did improve. I'll install the new bearings when I get home and see how they perform.
Chris
Edited by GuestThe fix for the Z bearing banding issues is to take them off your plate and clean them out thoroughly getting all oil and grease out. Oil can actually jam up the bearings a bit. But I'm not 100% convinced that's your banding problem.
I was finally able to disassemble my newer UM2 and install the new Z-bearings that FBRC8 sent. These new Misumi bearings are much better than the originals. My non-exact measure of excellence for these bearings: I'd hold one bearing horizontal in one hand, slide in a rod, and see how much I'd need to tilt the bearing to make the rod start sliding. The results were a few degrees for the original bearings, and I couldn't make the rod be still with the new bearings. It was like first time trying to ice skate... no matter what I tried, that rod would slide one way or the other.
After installing these into my system, the new UM2 system was now printing better than my older UM2. So I did a tune-up on the old system, and both are performing very well now.
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What model bearings you got? Sounds very interesting. I lov some misumi with my 3d prints 
This is the fantastic part FBRC8 sent:
C-LHFSW12 exactly, I was just checking the cad file from misumi vs the ultimaker 2 linear, misumi it's 1mm shorter on length. And the step file seems to fit like a globe.
Left Misumi Right Um2 step file
Thank you very much!
Edit: Wow 13€ each. Sure quality has a price. The C- version it's 7€ each... I will have to try, sure they must be better than the 2€ each I got.
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DAFUQ - You need to create an advanced account to order from Misumi. And not only that, they have two other account types and you can't upgrade from them to "advanced". I guess they don't really like customers. Rather old school purchasing agents who order 200000 pieces at once...
Btw. I think I have the same issue. Posted it here.
DAFUQ - You need to create an advanced account to order from Misumi. And not only that, they have two other account types and you can't upgrade from them to "advanced". I guess they don't really like customers. Rather old school purchasing agents who order 200000 pieces at once...
I had to pay 20€ for delivery... It should be cheaper for you since you are closer. And sinceI also ordered gears, they sent it onanither delivery so 20€ more... And I did choose the wait for all option. They indeed only care for 200000 orders. At least when my bed falls by itself I'm happier XD but they can be a pain. Too bad igus doesn't sell this bearings, not only they have a faster pay system, but they send much cheaper and they care for small orders. I got some shafts from igus and the quality was pretty good.
Btw @nicolinux you said you had igua filament. Maybe you can print them...
And if you are willing to check if they fit...
Igus has no balls XD
I wonder how much noiseless can they be...
Edited by Guest
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Hm, the problem is - I could live with the actual ones but I want them to be as perfect as possible. I originally though to print the z-nut too, but now I've ordered a new one for 5€. So I'd rather not print the bushings. The Tribo filament is hard to print with and for a simple linear bearing I had to do a crazy amount of iterations... I'd rather use this filament for some other lower priority purpose 
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For my tests on the faulty one. The linear bearings ain't a problem 'if' the nut it's perfect. If the nut woobles it leaves room for the bearings to stuck the z. If you never had z jump the bearings much be quite ok for the wooble nut you have.
Get the nut, if it doesn't wooble it will improve your lines already. A really bad bearing would have made big z jumps on your nut (lol).
But I can haz both for extra awesome printing qualities, right? 
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And if you are willing to check if they fit...
Igus has no balls XD
I wonder how much noiseless can they be...
Btw. I've used the igus linear bearings on a Delta and they were very silent. On the UM2 z-stage it doesn't make sense since the z-motor/thread is quite loud and one doesn't hear the linear bearings anyway.
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Indeed. That's what I aim too. That's why I changes my shafts to misumi, bearings, gt2. Any extra allows me to print a bit faster without loosing quality. My next step um2 hotend on umo+.
But yeah, misumi it's a pain but they deliver.
euhmm,..... ordered the bushings, delivered two days later and delivery costs € 0,00.....
Yeah @nicolinux also got delivery for 0€
Misumi must charge extra for spain customers
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Have you ever checked the bearings that are on the 2 thicker rods on the back?
Maybe there is something going on with those, (or one of them).
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