Roughness in Chinese HGR20s

[rocketflier]

Ordered a set of aliexpress HGR20s (they're the wide so that might not be the right designation) rails/blocks (2&4) for way way way too cheap. I only ordered the one set figuring it was too good to be true so I'm good with fiddling.

Some of the blocks have a distinct bearings moving feel and don't seem to slide that easily. I want to say they have a detent feel to them as it feels like it stops every <whatever the diameter of the BBs are>.

Initially I thought maybe lack of grease, but that showed up last night and that didn't help. Although my hands are silky smooth this morning.

Having no experience with this style of bearing, what should I be expecting in movement? Slides easily with finger pressure? No bearing movement feel at all?

If I pick 1 set up by a block such that the 800mm rail is verical, should the rail & other block slide down?

I didn't get a chance to research bearing size/preload, any good links for rebuilding/sizing?

thanks!!

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[rocketflier]

Well, I managed to knock out 1 ball, drop it to the floor twice and find it both times. It popped back in.

I wiped down 1 rail and greased and ran each block back and forth a bunch of times. There is still the feel of the balls moving, but the detent feeling is now very minor.

After watching more videos, I don't think they're as smooth as the original HIWIN. Most of the videos were the small setups 12, maybe 15s they were whizzing back and forth with a finger.

I can pick up the rail vertically with all 4 blocks on the 1 rail by one of the blocks. So it does take a bit of force to get them moving.

Debating ordering my Z set from another source for comparison. I've seen BST mentioned and did order a ballscrew set from them. Also auto-overstock. Thoughts?

[ger21]

If they are preloaded, like it sounds like, they won't feel smooth until they have a load on them.
I've heard that some of the chinese bearings can have metal chips in them, and are much better after cleaning. But cleaning them can be difficult, without losing all of the balls.

[jahnj0584]

basically all china parts get better after a cleaning, but the linear rails are never as smooth as hiwins. Ive tried both

[louieatienza]

basically all china parts get better after a cleaning, but the linear rails are never as smooth as hiwins. Ive tried both

HiWin is Taiwanese...

Usually, if the bearing races are smooth, the issue may be the BBs rubbing against each other. I would check the mfr's recommendation for grease/oil. High-speed low load applications may require oil instead of grease. I have some LM rails and blocks form H.S.A.C. and they're as smooth as the HiWin ones I have. Not as nicely ground as the THK rails and caged ball blocks I own however.

A lot of industrial machines go through a "warm-up" cycle before parts are actually machined, which is akin to stretching out before exercising. The LM system may perform differently once the parts have warmed up and the lubricant has a chance to flow, as opposed to just sliding back and forth with your hand...

[jahnj0584]

Never said they werent, but the offbrand ones are most likely china or asian at minimum.


Also be aware that Automation Overstock makes their own Hiwin dimension rails, in an ISO factory for a very reasonable price. I will be trying them on the next build for sure.