Sticky LM8UUs

I've just started building my Mendel90.

I'm currently working on the X idler assembly. After fitting the 2 LM8UU bearings I tried them out with a straight rod. I imagined the action would be silky smooth. It wasn't. Many sticky points. I could stand the rod vertically with the assembly stuck.

I used a different rod. Same result.

I forgot the idler assy and tried a single bearing on its own, just on a rod. Still many sticky points. Tried another bearing. Bit better. Still nowhere near silky smooth though.

If I use more than very gentle force everything is fine, the stickiness is fairly easily overcome.

Do I adjust my expectations and plod on, or should I do something to these rods/bearings to hopefully ease them up?

Yes linear bearings are quite lumpy when new. They get smoother when they have been run in.

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[www.hydraraptor.blogspot.com]

Thanks Chris. Expectations have been adjusted!

I think the reason is because linear bearings don't have a cage to separate the balls like rotary bearings so they rub against each other.

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[www.hydraraptor.blogspot.com]

Thanks Chris.

I spent a few minutes sliding the bearings to and fro and that helped marginally. Rotating the bearings on the shaft helped quite a lot. Nothing outstanding though. I expected a motion like the glide of my lathe's tailstock; these LM8UUs, even when not sticking, have a definite vibration - very off-putting!

I also hunted for lubrication tips. Not finding anything definitive, I decided to not use any and see how things go.

They come with lubrication. If they dry out (which the X axis ones tend do do from the heat of the bed when printing ABS) then I add car engine oil.

Yes they do vibrate and are noisy. The alternatives are bushings, which have slop, and ball bearings used as rollers like the original Mendel. They work very well but fell out of favour due to the complexity and cost.

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[www.hydraraptor.blogspot.com]