SBR20LUU seal interference

[threedee]

My bearing block is double length, two cartridges.
The interference is starting after moving it along fast, as if rubber catches the rail and bends in introducing friction. It is a medium sized laser cutter, not much load, but i need it as "freewheeling" as possible. The gantry is moved by nema17 motor, so any interference is not good.

I have "exercised" the bearing a bit by moving it by hand, it loosened some. Torqued the retaining set screws etc. For now its good, but i just want to know what happens if i remove/cut grease seals.

[Lee Roberts]

Hiya, yea just found your other thread about rebuilding it (Rebuilding terribly engineered laser cutter) so got a better idea what your dealing with now...

You can't take the rubber seals out as they keep the balls retained but you could trim the outer most part that is bending, the bit that rides the rail and stops swaf getting in.

Non of the ones I've handled had this problem and I've handled quite a few!, I'm wondering if they've used the wrong size rail and that's the real problem, can you mic the rail and get a proper dimension off it ?

If you look at the rubber seal on the ends of the bearings (where the snap ring lives) it should give you the sizing, something like SBR12UU.

They may have done something stupid like used 12mm bearings with 1/2" rail... I could be wrong.

[threedee]

You're mixing things a bit - original rail is hanging rail (support only on ends), just a 12mm round bar. Original bearing is LM12UU but its 57mm long (double cartridge as well ?).

The rail i'm replacing it with is supported SBR20 with 20LUU bearing.

Dont have a micrometer, but original rail is spot on 12mm. Bearing is still a bit loose though...
Using genuine Mitutoyo 150mm vernier caliper.

[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...