View Full Version : Linear bearings: I checked the X motions for smoothness while I had my belt off and

Joseph Shawa
09-25-2017, 8:39 PM
found that the motion wasn't what I would expect from a precision instrument so I tried to take it apart while on the rail and apply lubricant directly into it.... not knowing what I was getting into.
Fortunately I had the foresight to put a baking pan below and didn't feel quite the fool when the ball bearings started spilling out.
I took the rail off and slid the linear bearing off and proceeded to reassemble the thing.
Good thing I have high power glasses and a microscope as the parts in there a DANG SMALL!
About an hour later I got a hundred little tiny bearing back in and got it all back together and put it back onto the rail.....still not what I would expect. It was kind of a JITTERY grabby feeling. So going back to my skateboarding days when I used to replace my worn ball bearings with BBs and because they were slightly over sized the wheels would kind of turn with a bit of a un-smooth JITTERY feel. So I did to my linear bearing what I did back then and remove ONE ball bearing from each of the four slots. I tried it again and voilla! Smooth gliding with no loose play as one would expect from a precision device. Now, I'm not sure if they packed Four extra balls into it by mistake or they expected it to wear out and get smoother over time but I am much happier now with four less.

Kev Williams
09-25-2017, 10:10 PM
I just went thru this with my GCC as the rail bearing was pretty sloppy...

How old is the machine?
What did you lube the bearings with?

I just put my new bearing on last week. I'm sure it's doing what yours is doing; as you slide it along the rail, it's 'bumpy'... yes?

This issue is likely just bearing pre-load. Mine new bearing is very tight, to the point it sounds and feels like running fingernails along a washboard. The preload is due to the rubber seal/dirt wiper, which will wear down in time. The balls themselves will also wear down in time. How much time? I'm not sure, but my washboard noise gets a bit less each day.

So- by removing 2 bearings from each side you removed the pre-load, and it's gliding much easier. But, the 4 slots are actually 2 circular raceways, so each raceway is short TWO balls. One of the reasons my old bearing was so loose was it was spitting out bearings. There's 2 reasons these things will spit bearings: 1, Dirt buildup being forced into the raceways leaving no room for all the bearings, and 2, missing bearings, which leave a large enough space for others to easily fall or be pushed out. (This is what the bearing place explained to me). My bearing was spitting out bearings, because several months ago I'd taken mine apart to check it out, and didn't get them all back in. After that I found 2 bearings on the table at different times.

What actually wears out most in these bearings is the rubber seal. When new they're tight, then wear themselves down and pretty soon everything is snug without being tight and slides freely along the rail. Dust and dirt wear out the rubber and bearing balls after awhile, and the rubber hardens with age. I'm sure yours are still breaking in, and it might be wise to replace the bearings, at least 1 per side...

I was also told rail bearings do NOT like grease, or even much oil. Grease will cause the bearings to slide rather than roll, and grease collects dirt very quickly and force out balls. They like very light oil, and very sparingly. I was told to just keep the rail clean, and add some very light oil to the bearing maybe once per year. I can't argue with that, I've never lubed the rail bearings on my 13 year old LS900 and they slide like ice on ice with no free play..

Joseph Shawa
09-27-2017, 1:52 PM
Hi Kev. Nice response. Thanks for the info.

Yes. Same description of binding bearings. I have had the machine for 2 years but have done mostly cutting and little engraving. Just getting into 3D Maps. So, relatively little wear?
I can't see how having one less bearing will cause it to spit out bearings but right now I am happy with the results. Will let you know if I find any problems.
I used a Very light high tech spray from 3M.

Kev Williams
09-27-2017, 2:15 PM
- having less bearings just provides more room for them to escape - as long as everything is clean and rolling smooth they'll likely be fine, but check the bottom of the machine once in a while :)

Joseph Shawa
09-27-2017, 7:44 PM
Actually, in my bearing there are end caps and I cannot see a way for them to escape. They are sealed. The only time they escaped was when I took the housing apart.