Linear bearings

I am trying to use linear bearings Lm8uu on my x axis smooth rods.
They slid very rough by themselves and are very hard to move when attached to the x axis base plate.
The rods are imp and measure 7.65mm not chromed.
Any suggestions how to make them slide smoother?

Try a drop of oil, I use precision 8mm rods without issue, if anything 5/16 rods should be loose.
They feel worse on the base plate because you get the combined resistance and it's unlikely the rods and bearings are accurately aligned.

LM8UU's will not ride properly on 5/16" rod. Even if everything is aligned properly. They require a properly sized rod for the ball bearings to seat properly in the channels.

You must use Metric Tool Steel Tight Tolerance Rod with these
bearings. (McMaster Item 88625K67 - 3' lengths)

In the US McMaster-Carr on www.mcmaster.com is a good source
for the Metric rod: pick a distribution point nearest you. I used eBay
for the bearings, with free shipping from China/Hong Kong.

Thanks for the help, I will try metric 8mm rods and post the findings.

ooh...did I purchase the wrong rod then? I didn't bother with the annealed variety, considering the low expected loading, and just purchased the McMaster part #3180T14 to save a few dollars. Bad choice, or negligible difference?

"You must"

xiando Wrote:
-------------------------------------------------------
> ooh...did I purchase the wrong rod then? I didn't
> bother with the annealed variety, considering the
> low expected loading, and just purchased the
> McMaster part #3180T14 to save a few dollars. Bad
> choice, or negligible difference?

If that's the part number you purchased, you spent a lot more than you really needed to. But the part number you listed will work perfectly fine, and is in fact higher tolerance than what most people use.

xiando,

looks like you have the more expensive, 'harder' version, of 8mm stainless rod. you should be fine. you could save a few dollars ordering the other part number.

biggest issue i would see is trying to use 5/16 with 8mm bearings. Even with 8mm rod, my ebay bearings aren't exactly smooth as silk.

"biggest issue i would see is trying to use 5/16 with 8mm bearings. "

I agree. there's too much play and the bearings can''t seat properly, leading to slide rather than roll. One could argue that he could get away with the printed bearings, but I don't want this to devolve into a specious debate.

"and is in fact higher tolerance than what most people use."

yup. I'm fully aware of the difference. Sorry, I was trying to be tongue-in-cheek regarding the "you must" comment accompanied with a very specific part number, but perhaps a bit too dry about it... There is no "must" aside from 8mm smooth rod (not btw limited to steel rod with certain restrictions) and a particular persons' expectation of performance and operating environment, in part only limited by available kitting.

Okay, got my new 8mm rods in.
It is worse now then with the 5/16" rods.
Any ideas?

Have you packed the bearings or otherwise lubricated them? If so, my guess would be that they're misaligned, the rods are misaligned, or both are.

Slauziere,
How are your prints?
With a rough x I don't get good precision.
Any thoughts on bronze / brass bushings

Take your caliper and measure between the rods at each end of the X, mine read 42.38mm & 42.25mm and it's SMOOTH as glass, I use Royal Purple Max Gear 75w90 as my lube... (it makes a difference for sure), if your not sure how to use a caliper correctly, you need to wiggle the caliper back and forth with pressure on it until you see the LOWEST measurement, that is the correct measurement. I would guess these cheap chineese bearings have quite a bit of "slop" so you can actually get away with quite abit of miss-alignment, so yours is either drastically bad, or your looking at a badly printed X carrage...