View Full Version : SBR20LUU seal interference

19-07-2019, 02:06 AM
Rebuilding laser cutters Y axis.
Bought 20mm supported round rail and a bearing block with 2 cartridges in it.
The motion is being restricted by rubber seals rubbing against the rail.
Axis at the moment is driven by nema17 motor and that kind of interference may impact motion.
Can i remove the side seals off of the block ? Or at least trim them back a bit ?
Or is it just my inner idiot speaking ?

Bearings were cheap, can always replace, just wondering by how much would it impact running it in smoky environment with occasional manual wipedown of the rail.... Dont want to destroy the only one i got at the moment.

Lee Roberts
01-08-2019, 12:02 PM

The rubber seals are designed to be a snug fit and "rub" the rail, the friction from this wont be anything to worry about...

when you say restricted...by how much? are you sure something else isn't amiss?

Yea you could remove the seals from the SBR bearing units, first though have you checked the little grub screws on each unit to make sure they haven't been over tightened, these allow you to take up slack in the bearing fit and if you go to far it starts to bind.

Just find the sweet spot and then keep checking regularly as part of maintenance for this rail system, use oil after the wipe down.

You can see what I mean in the pic below.

01-08-2019, 02:09 PM
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
01-08-2019, 06:52 PM
Hiya, yea just found your other thread about rebuilding it (Rebuilding terribly engineered laser cutter (http://www.mycncuk.com/threads/12856-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.

01-08-2019, 07:07 PM
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
01-08-2019, 08:30 PM
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...

01-08-2019, 08:59 PM
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...