SBR20LUU seal interference

[Lee Roberts]

Ahh ok, don't know what else to suggest then mate sorry, assuming you've checked for crap in the ball circuit's...common problem with the cheaper stuff...

[threedee]

At this point i'm committed to replacing rail/bearing anyway.
As for SBR20LUU, all balls are moving freely as much as i can tell by moving them with my finger. Doesnt look to be snagging anywhere, rail is clean and without scratches and definitely hardened (cutting it to length was a pain).
Is plastic ball housing a norm in bearings of this kind ? How much more expensive can 20mm LUU get ? Are metal housings a thing in these ? What even constitutes quality bearing of this kind ? I've no idea, never have been this involved with linear motion before...