linear bearings

How lose should the lm8uu bearings be? I'm thinking mine are too tight. On a vertical rod, the bearings will stay in place with the weight of the motor instead of sliding down.

Linear bearings are meant to run precision hard ground shafts Thompson is a brand. People here use stainless round stock or people use drill rod: or cold roll nothing but the precision ground shaft is correct

This is what I'm using: rods It's supposed to be precision ground. From what I can tell it appears to be.

Edited 1 time(s). Last edit at 10/09/2013 12:09AM by nemo000111.

There is an online bearing Company called vxb they have bearings and shafting under linear bearings cheap. And if you need to cut them you have to use abrasive cutoff wheel a saw won't cut through hardened outside

Edited 1 time(s). Last edit at 10/09/2013 12:22AM by cnc dick.

Thanks. I looked at them earlier and they were rather pricey ($6 per bearing and the rods cost about 5x as much as what I got). If I have to go that route, so be it though. I'm hoping I got a bad batch of bearings (ebay). Based on the calipers I've got, the rod is within spec. Anybody have any experience with the rod I'm using? Ultimately though, is is only an interim setup. I'm building the prusa i3 boxed version and once it's up and running I'm going to design and print parts to use a square aluminum tube frame.

The rods you bought our annealed the outside is not hardend. Plus you would need a good micrometer to do the measurement buy the correct rods

Yes, those bearing seem unusually tight.

The rubber seals on those cheap LM8UU bearings are very sticky. I've noticed they slack off a lot after a few days or more. I'm also using inexpensive drill rod. I've checked them, they are accurate, but each batch is slightly different. The bearings usually have a bit of play in them, they are not very accurate overall.

If any contamination gets into them, they can bind up pretty bad. They then need to be flushed out to work properly again.

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Yvan

Singularity Machine

meassure rod diameter, it should be about 7.96-7.99 mm. also, try cleaning the bearing and put some grease in. maybe you got some dirt(dust, sand etc) inside bearing..

I too use O1 drill rod. Eventually the bearing will wear tracks into the rods, but they work to get you going. Form my LM's I like to lube them with some thin oil (not WD40) and then take a spare piece of rod and run them up and down by hand several times to loosen them up. You will be able to feel the difference, if not keep going until you do. Also, I try to rotate them around the rod to encourge any stuck balls to spin freely. The pacing grease they use can get stiff and collect dust so worst case would be to soak them in degreaser then reapply oil. Also, same some trouble and make sure the end of your rod has a chamfer to prevent knocking the balls out of the LM's when you slide them on.

I did just buy some stainless rod from SmallParts on Amazon to replace these, but the printer is still printing well so I haven't done it yet.

-Jay