3D Printer Problems - LM8UU bearings

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Will McElderry

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May 19, 2015, 9:22:14 AM5/19/15
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Hi All,

I've had a couple of issues with my Y axis intermittently on my prusa
i2, and today I've got to the bottom of it because it's not intermittent
any more... The LM8UU linear bearings on one rail like going in one
direction but not the other. They resist quite firmly when pushing one
way, the other direction they glide like normal. That happens even after
disconnecting them from the Y carriage - so it rules out misaligned rods.

They used to glide fine after both build & recent rebuild (partly
inspired by this issue but it was intermittent then and consequently not
identified).

I'm guessing lubrication may help, but a little puzzled by the specific
issue and not sure if replacement would be better in the long term (is
it possibly a sign of damage - perhaps caused by not lubricating to date?)

Rebuilding will be painful - I've just rebuilt once and I'm going to
have to rebuild to lubricate - should I just replace now?

Has anyone had any issues like this or knowledge of best way to treat lm8uu?

I've just read:
http://reprap.org/wiki/Linear_bearing

That indicates some bearings are packaged in 'cosmoline' to avoid
rusting which is sticky. Mine were packaged in some liquid, I'd assumed
it was lubricant...

Anyone got any thoughts?

Thanks,

Will.

Colin Jones

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May 20, 2015, 8:34:00 AM5/20/15
to north-ea...@googlegroups.com, wi...@mcelderry.com
I've seen this on the LM8UUs from China. Some will move freely, some only one way. Some are happy to rotate both ways on the bar, others one way only.
A slightly smaller or smoother bar will free them up. I bought extra and matched them up to the bars.

If you don't want to dismantle the printer, try rubbing down the bar with fine emery. A bit of oil would help also.

Cheers,
Colin

Will McElderry

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May 22, 2015, 4:32:42 AM5/22/15
to Makerspace
Thanks Colin,

I'll give this a go and see what happens (and report back in case it helps anyone).

I've got some more lm8uus on order too, so I'll have a backup plan.

W.
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