LM8UU on 5/16" rod?

Has anyone tried these bearings on a 5/16" rod? Are they just too big?

I'd rather avoid having to source some 8mm smooth rod here in the US.

If not, does anyone know if there are there linear bearings that will fit 5/16?

I was able to find suppliers for SW4 ball bushings (1/4 or 4/16 inch) and SW6 ball bushings (3/8 or 6/16) inch, which would imply that the part you're looking for would be a SW5 ball bushing.

Unfortunately, googling "SW5 ball bushing" doesn't come up with any useful hits, so I suspect that no one makes one that size.

Since the Chinese bearing manufacturers seem to focus on metric parts, I suspect that switching to 8mm rod and bearings would be less expensive than switching to 3/8 rod and bearings.

Another option would be to build Sells style bearings - you'll find that they slide along the rail more freely than LM8UUs do, but getting them fitted without side play can be tricky.

It will do fine. You will have an additional slop of +/-0.03125mm, but this is below the repeatability of the machine.

Ok, thanks - was able to get the 8mm's relatively inexpensively (12 for under $25, shipped).

I shouldn't worry about that amount of slop, I guess. Didn't even think to calculate difference against the machine tolerance...

Edited 1 time(s). Last edit at 08/10/2011 06:18PM by TheCase.

I think it's still a good idea to find 8mm rod for them, if you can. The lifetime of the bearing will likely be shortened by using 7/16" rod, because the bearing won't have its proper preload.

You might be right. I'm not sure if its because they are poorly made bearings (China), but they certainly don't seem to travel as smoothly as I would have thought.

Perhaps they are just packed with thick grease that needs to be worked out or something...

I just happen to already have some 8mm smooth rod on the way... we'll see how they perform on that...

I find they run very rough when new but soon wear in and become very smooth with use (on 8mm rod).

Edited 1 time(s). Last edit at 08/27/2011 04:52AM by nophead.

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[www.hydraraptor.blogspot.com]

Finally giving the 8mm rod a try.

nophead, I think "very rough" is an understatement! I don't think they will ever run smooth. At least not to the point where they will move freely under their own weight.

I was already getting some backlash with the bearings with the 5/16" rod - the Y-axis was just a bit sticky and you could tell it would jerk from a dead stop on small distances. This feels like its 10 times more stubborn. I think I'll hit the rod with some steel wool and grease it up really good - perhaps time will tell.

Like nophead, my LM8UU bearings were very tight when I first installed them - lubing up the rails with some silicone/teflon spray helped a bit, but there was still a lot of friction. Running some prints loosened things up to the point where the x-axis will move under gravity now if the belt is removed.

Finally printed up the LM8UU X carriage - replaced the 5/16" X rods with the 8mm and went for it. I'm still doing my best to ignore that it snags like hell, and also the fact that two little balls popped out of one of the bearings... (good thing I ordered 12 bearings and I only really need 11).

Initial prints are my best ever! All perimeter walls on the X axis are damn near perfect. The stepper has yet to slip (my biggest fear) - and I didn't even have to turn up the pot on the driver.

Thanks for the reassurance folks! Now to print the new Z carriage parts!

Edited 1 time(s). Last edit at 09/16/2011 02:05AM by TheCase.

Wow. One of the bearings is cutting a groove in the smooth rod.

I just put one of Greg Frost's LM8UU carriages on 5/16" rod and there is quite a bit of slop. Once you magnify it by the length of the hot end it's too much to print. I happened to have a full set of 8mm rods unused so I swapped them out and the difference is night and day. There is still more slop than 5/16" rod with 5/16" brash bushings, but of course the motion is also much smoother. I think with 4 LM8UU the slop could be reduced.

TheCase Wrote:
-------------------------------------------------------
> Ok, thanks - was able to get the 8mm's relatively
> inexpensively (12 for under $25, shipped).

Where'd you find your 8mm rod? I'm in the states and having trouble sourcing some.

I got the rod from lulzbots,

[www.lulzbot.com]

But it was much cheaper ($25) when I bought it a few months ago. So it didn't matter that I didn't need the threaded rod from the set.

If you have a Fastenal in your area, you should be able to special order in-store to avoid the shipping charges.

[www.fastenal.com]

You'll need 3 pieces.

TheCase Wrote:
-------------------------------------------------------
> I got the rod from lulzbots,
>
> [www.lulzbot.com]
> et.html
>
> But it was much cheaper ($25) when I bought it a
> few months ago. So it didn't matter that I didn't
> need the threaded rod from the set.
>
> If you have a Fastenal in your area, you should be
> able to special order in-store to avoid the
> shipping charges.
>
> [www.fastenal.com]
> =46956&ucst=t
>
> You'll need 3 pieces.

Fastenal close by.
Thanks!!!

Has anyone tried the adjustable type of LM8UU with the slit in it?

Ebay calls it LM8UUAJ, but it also might be called LM8UU-AJ or LM8AJ.

It seems like maybe you could just clamp it with a hose clamp to remove slop on a 5/16" rod.