Replacing polymer bearings on the X axis on the Mini

Hello this is my second day as a 3D printer owner and need some basic help. Bought a used Mini that was listed as having possible issues but was not testing. Figured I would roll the dice and fix it myself. Well I ran into a couple that I could see very quickly after messing with it a little.

The big one is the X axis the extruder runs on move jerky as I found when I tried to run my first print and it had issues making it over to the cleaning pad to clean and run calibrations, then it would try to touch the end of the bed to calibrate and miss and just dig into the bed. I checked the belt and gears and they looked fine with no slipping. I thought maybe the motor but when I turned off the system and moved the extruder by hand I noticed it didn’t glide on the rails all that well and felt a little sticky especially compared to the Y axis when pushing the bed. So I figure now it is the polymer bearings and thought either I need to adjust them or replace them.

Lulzbot does not specifically list replacement bearings for the Mini in the parts list so not sure if they sell them in a size for the Mini or not and need some guidance on where to find them. Also if at all possible some instructions on replacing them or if possible just readjusting them. Not brave enough yet to rip it apart just yet without first seeing if someone with more experienced has some advice as this does not look to be a simple part replacement.

Thanks in advance for help.

The Mini uses 8mm rods, so you are probably going to want an Igus LM8uu bearing. THe exact ones used in the Mini from the factory are listed in the BOM file (Bill of Materials) which can be opened by Microsoft Excel

Thank you piercet, I was able to find the part based off your link on Amazon.

I spoke with support and described the situation and said the unit he had felt a little sticky when moving the extruder by hand compared to moving the bed and said I should try replacing the motor first with one of the new ones they offer on the site:

Regardless the PEI sheet needed replaced so figured I would just add it on as well and see what happens, worse case I have an extra motor laying around. But has anyone changed out these bearings on the Minis before if so I would be interested to know if there is any documentation on it in case the motor is a dead end.

Okay just messing with the X axis again and noticed something, its not just jerky when sliding the exturder back and forth but I noticed most of the problems sliding back and forth took place at the first two inches on the left of the axis where home is. When the extruder got within two inches of the wall it would noticeably slow down and struggle to get to the end.

I tried to move it by hand left and right and noticed with just enough force to move the extruder it would slide with some resistance till it got close to the wall and then I would have to exert enough force to move the extruder that it would lift one side of the frame off the table.

Does anyone else notice this when pushing the extruder back and forth on the X-axis on their minis? I am still not totally convinced it is going to be fixed by putting a new motor on it. Even if it does fix it by having enough force to push it to the end I would still think it would effect the print having uneven resistance across the X axis.

If it’s getting difficult to move when it gets closer to the motor or idler side of the X axis, that can indicate an allignment issue. Either the motor is out of position (does the mini have adjustment slots there?), the motor pully is too far in or out on the shaft, the idler bearing is out of allignment for some reason. The belt could be in the wrong spot on the x carriage belt clamps too. Check the belt allignment when you get close to where it is getting difficult to move and see if anything looks off.


in Addition to piercet’s suggestions:
there is a chance that the X assembly is not leveled.
Can you check distance of Extruder to bed on left and right side? They should be almost the same.

All the Best

I have replace those bearings before and I do not remember ever finding anything to follow. But the top pair can be a bear to remove! I would say look very closely at the X axis parts and make sure one or both of them are not cracked/broken from the sounds of the issue you are seeing.

+1 I also agree that it sounds like an alignment issue if it only sticks near the homing spot. I highly doubt a new motor is what you need, but that is just my opinion and i could be wrong.

But in the off chance that you do need some new bearings here are your options:

LM8UU compatible mini parts. Although the ball bearing mod will work it will eventually chew up the soft steel rods that are default.

STL for experimental 3d printable linear bearings. I’ve heard that the 8.1 ID file may work well. I just received a free sample of IGUS new tribo filament that i plan to try soon.

Just wanted to thank you guys for the support and trouble shooting this issue, and to post an update on my progress. So I bought a caliper and measured the bar spacing on the x-axis and they came out very close to even so neither side looked to be off. So I decided just to wait for the new motor to show up and give it a shot before I tried anything else. When it came I took off the belt to replace the motor I tried moving the extrude along the bars and it ran smooth! So then the checked the metal bearings adjacent to the motor on the other end of the x-axis and they moved fine as well so the only other thing attached to the belt was the motor so I felt pretty confident at that point it was the motor as support suggested.

Got it switched out and was finally able to make my roctopus! Printed a few more things since with great luck.

Good to see you got it working :wink:

I replaced my Y and X-axis bearings (with LM8UU ball-bearings) today using Biolumo’s 15mm OD edits of the bearing holders on thingiverse and must say this is one hell of an upgrade for the mini! Rotational (bed) and Z-axis slack are drastically reduced (if not gone) now.
It was a pain to get hold of the parts (especially the hot inserts since I live in Europe) but it was worth all the hassle and wait.

Make sure you replace the rods with harder rods as well, or you’ll be replacing the rods and the bearings in a few months.

I carefully read up on the topics and did, thx! The hardest part of the upgrade was shortening the 35cm rods I ordered. Never would have thought I’d need an angle grinder for a 3D printer upgrade :wink:

You would be suprised how many of them can use that haha! It’s the ones that require a cutting laser that should start to worry you

So two questions.

  1. why replace the polymer bearings? My understanding they are superior to the Ball bearing ones?
  2. what does replacing or upgrading the X axis stepper do? Is it more accurate? or just a replacement for a bad stepper?

For me, the “slack” in Z-axis was unacceptable high. I could push up the extruder with the tip of my finger easily and I had non-flat finishing layers on top. I suspected this was due to drag forces tilting the extruder depending on the print direction. Also, when removing a print from the bed I could easily rotate the bed some. Although I never did any scientific research, the results seem to have more precision and printing seems more “rigid” and precise. I admit it’s mostly based on gut-feeling, but for me, it feels good and that’s also an important part of my 3D print hobby.

I can’t say anything about replacing the x-axis stepper, only the dampener on Y. That’s a big gain in terms of print noise and added a lot to the WAF of the Mini.

Can you please share source for rods appropriate for use with the steel ball bearings?

I’m from Europe/Netherlands so I don’t think my resource is of any use to you, but the good news is: just any hardened steel rods (of the correct diameter) should do the trick.

Know if Lulzbot Mini is shipped with the equivalent “Standard” or “High Precision” itWorks bearings?

Mini 1 would have been the standard RJM IGUS bearings. I don’t know about Mini 2. Regardless, if you are going back with IGUS bearings, go with the RJMP “precision” style. They fit the rods much better.