Damage to linear motion rails / Bearing wear

[benkrall]

I am posting some pictures of damage to the steel linear motion rails. The bearings are digging and compressing the linear motion rail enough to pile up material outside the bearing contact area, and send foil-like steel material off the axis and onto the work.

I am having this issue on the INSIDE of the A-axis rail, the OUTSIDE of the Y-axis rail, and the TOP of the X-axis rail, and not for the entire length of the rails, just parts where the bearing/rail alignment is somehow off.

Additionally there is a lot of "clicking" and "creaking" that I have narrowed down to several linear motion carriage bearings, which I assume are totalled inside.

The axes all seem to be operating well even though the rails are getting damaged. Everything is still cutting dimensionally with no noticeable issues like missed steps.


Can anyone give any advice why this might be happening and how I can solve it?

• I am going to replace all the linear motion carriage bearings, hopefully today. Except for the ones that are build into the carriage, I don't see how to replace them.
• Should I also FLIP the linear motion rails so that the undamaged parts are contacting the bearings?
• Do the bearings need to be changed to 10mm wide or more, to provide less loading on the steel rail? The loading somehow is damaging the rail.

Thanks for your advice!

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[ger21]

It's happening because you have hard bearings rolling on soft steel. And there is probably some minor misalignment.
It's a low cost linear rail system, using components that are not designed to be used that way.

I would flip them around to use clean edges, and align everything as good as you can, so that the bearings are perpendicular to the steel. That's about all you can do. If they get too worn, replace them.

[benkrall]

I would flip them around to use clean edges, and align everything as good as you can, so that the bearings are perpendicular to the steel. That's about all you can do. If they get too worn, replace them.

Thanks,

OK - so it's relatively normal? I am having trouble understanding what's the threshold of when this is a problem.

I can't measure much of a difference in thickness with calipers on the rails. The bearing clicking is more worrying.

My instinct is to work on it now but would some people keep running it like this no problem?

BK

[FineLineAuto]

Thanks,

OK - so it's relatively normal? I am having trouble understanding what's the threshold of when this is a problem.

I can't measure much of a difference in thickness with calipers on the rails. The bearing clicking is more worrying.

My instinct is to work on it now but would some people keep running it like this no problem?

BK

Ben,

Normally I see that happen when the bearings are over tightened against the rail or they are cracked. Did you check for hairline cracks along the bearing face? I would swap the bearings out for new ones when you get a chance. Also, are you keeping the bearings clean of debris?

I can send you some new bearings.

[benkrall]

Ben,

Normally I see that happen when the bearings are over tightened against the rail or they are cracked. Did you check for hairline cracks along the bearing face? I would swap the bearings out for new ones when you get a chance. Also, are you keeping the bearings clean of debris?

I have had trouble getting the right tightness on the bearings. Sometimes the lower bearings do not spin even though they contact other places on the rail. I have allowed it a little less tightness against the rail since not all the bearings always contact fully. My Y-axis rails are as flat as I know how to get them. There may be tiny high spot but the missing contact on the adjustable bearings is intermittent.

I don't see any cracks in the bearing face for sure

I wipe the bearings and rails clean regularly to remove everything

I'm in the process of replacing all the bearings and flipping the linear motion rails so the loaded side is the best surface.

What is the critical dimension of the carriage bearing vs. the linear motion rail?

I would like to tighten the lock washer completely against the carriage to eliminate any possibility of wobble from the lock washer only contacting the bearing in one spot. (the GREEN dimension) But if I tighten it fully, the bearing overhangs the edge of the motion rail which does not seem right. (this is the BLUE dimension)

Thanks,
BK

[FineLineAuto]

I have had trouble getting the right tightness on the bearings. Sometimes the lower bearings do not spin even though they contact other places on the rail. I have allowed it a little less tightness against the rail since not all the bearings always contact fully. My Y-axis rails are as flat as I know how to get them. There may be tiny high spot but the missing contact on the adjustable bearings is intermittent.

I don't see any cracks in the bearing face for sure

I wipe the bearings and rails clean regularly to remove everything

I'm in the process of replacing all the bearings and flipping the linear motion rails so the loaded side is the best surface.

What is the critical dimension of the carriage bearing vs. the linear motion rail?

I would like to tighten the lock washer completely against the carriage to eliminate any possibility of wobble from the lock washer only contacting the bearing in one spot. (the GREEN dimension) But if I tighten it fully, the bearing overhangs the edge of the motion rail which does not seem right. (this is the BLUE dimension)

Thanks,
BK

Ben,

The bearings won't all touch at the same time because each side of the gantry is over constrained with 2 carriage. This is normal and shouldn't affect the operation as long as some of the bearings are contacting the rail throughout the entire process. I would roll the gantry along the rail until you find the tight spots and adjust the carriage bearing according to the top rail.

[benkrall]

This is normal and shouldn't affect the operation as long as some of the bearings are contacting the rail throughout the entire process. I would roll the gantry along the rail until you find the tight spots and adjust the carriage bearing according to the top rail.

Thanks,
So is it OK to completely tighten the lock washer flat against the carriage, or is it more important for the bearing to be completely in contact with the rail:

lock washer tension to position bearing flush


lock washer tightened to carriage


or should I look for some shim washer solution to allow the lock washer to be tight and the bearing positioned exactly on the rail?

I can see the bearings wobbling back and forth when the axis changes direction, since the lock washer seems to create a fulcrum. Maybe this is not even a big deal but I thought it was contributing to the rail wear

Thanks again for your advice

[Eldon_Joh]

I don't know what i would do in your situation.

one thing i would consider is doubling the number of bearings, which would require drilling more holes. the holes don't have to be aligned perfectly, if for example, in post number 5, first photo, you install a set screw where the green arrow is in the block of aluminum "A" you can then adjust the set screw to push the bolt around inside the hole.

the lock washers could be replaced with beleville washers or just get rid of them and use regular washers.


definitely use an oil stone, or a fine file to remove the metal shavings, burs and high spots from the steel linear surfaces, but if that metal is yielding under the cutting force (which i doubt) then only by doubling the number of or using larger diameter bearings will solve the problem.

my guess is the metal is yielding only where it is under a lot of static load, so just stone off the burs and replace the bearings as needed.

[benkrall]

but if that metal is yielding under the cutting force (which i doubt) then only by doubling the number of or using larger diameter bearings will solve the problem.

my guess is the metal is yielding only where it is under a lot of static load, so just stone off the burs and replace the bearings as needed.

Some of the wear on rails could be due to operating loads, but I don't really run at high IPM speeds.

The carriage is pre-drilled so I can't really add any more bearings. I don't think this should be needed, tons of people running this system with the regular CRP carriage.

If this is the expected wear condition then that's fine, I'll monitor the bearings and buy new rails when needed. I just don't know anything about the wear conditions & risks cause I'm new to this.

I also don't want the machine to eat itself or knock out of true because of some burr on the rail somewhere. Also there are a few tight clearances in other places that would be disastrous if they connected at running speeds. So really don't want anything to move around

[benkrall]

Here are some pictures of how I ended up doing this.

• cleaned, deburred, flipped, rotated X,Y,A axis linear motion rails
• replaced all bearings with ABEC-9, probably super cheap but seemed to have less runout
• replaced upper/outer bearing hardware with different lock washer setup, this positions the bearing exactly on the rail but allows it to be fully tightened very parallel to the carriage

• fully tightened lower/inner bearing hardware to provide clearance vs. aluminum frame. well it would be better if the bottom bearings were fully on the rail but it's probably fine, since there's not enough clearance to put 2 washers.

I also don't want the machine to eat itself or knock out of true because of some burr on the rail somewhere. Also there are a few tight clearances in other places that would be disastrous if they connected at running speeds. So really don't want anything to move around

so, this may have been totally unnecessary but the axes are rolling smoothly now and the bearings are not clicking or wobbling out of alignment at all.

[benkrall]

so, this may have been totally unnecessary but the axes are rolling smoothly now and the bearings are not clicking or wobbling out of alignment at all.

So has anyone else had this kind of alignment issue with the old style FLA kits?

I have no frame of reference about why these clearances seemed so off with my build

[alan_3301]

Totally normal for that setup. skate bearings on CRS isn't really a precision system, but it works amazingly well for what it is.