New MK3S and Linear Bearings  

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justin.pierson
(@justin-pierson)
Active Member

Hello everyone, I am trying to figure out an issue I am having with my brand new MK3S and its linear bearings.

I got my new mk3s about two weeks ago, the build went smoothly I followed the instructions and read the online guide and also watched a few videos on the gotchas. I took me about 6-7 hours (I had some extra tools to help) and after running the wizard was ready to print. I printed a few small items off of the card with no issues, and was ready to print a benchy and up to that point was very impressed (coming from a few ender 3 frankenprinters) by the quality, then the issues started. During the print of the benchy I noticed an scraping/rattling sound which sounded like something was loose and rattling (metal to metal) so I cancelled that print (after checking the LCD) and set out to go over all the steps again. I narrowed it down to the two bearings on the left side of the Y carriage, so I loosened and hand tightened the holders, pulled the rods and packed the bearings, this helped but after a few more minutes the scraping would start again. I eventually moved those two and swapped them for two on the z axis and that helped, but the noise never went away. I also noticed that the Y carriage had a little bit of play, you could wiggle the frame about 1-2mm, which on the Ender 3 meant you did something wrong and needed to adjust something. I contacted support they sent me some new bearings and those were a lot better. Here is what I have found so far and I wonder if anyone else is having this issue.

  1.  The original bearings seem to be misumi bearings, they have made in Vietnam and a W/M logo on them, and have a part of LMU8. After looking online I found a match to the picture.
    1. If you run these bearing along a rod, you can feel a slight resistance like something is binding up, this also creates a vibration down the rod and if you put any pressure on it the vibration gets worse. I had assumed there should be no resistance and they should be perfectly smooth. (otherwise why even use them?) More grease does not seem to help.
    2. Some of the bearings work better in one orientation when they are aligned with the casing facing up, and with these if they are not aligned this way the vibration is much worse.
    3. Other bearings vibrate no matter what and you can hear a metallic scraping.
    4. And there are a couple of bearings that just scrape and feel gritty along the rod.
    5. I even soaked one with IPA and repacked with clean freshly opened grease and that didn't help.
  2. The new bearing have no markings on them and are much smoother but still feel like there is some resistance if just slight (I have checked the rods and cleaned them)
    1. They don't seem to have that same issue where it need to be perfectly aligned problem as the old ones.

 

I am in the process of printing and setting PLA versions of these bearings (with PTFE lube) which from my initial tests seem to work perfectly and super smooth, I also ordered a set of the polymer ones to see if they are any better. Has anyone else seen issues like this? Other than experimentation and trial and error I am not sure what else can be done. Is this normal for these bearings? 

This topic was modified 2 months ago 2 times by justin.pierson
Posted : 11/07/2020 1:10 pm
Karl Herbert
(@karl-herbert)
Famed Member
Posted by: @justin-pierson

Hello everyone, I am trying to figure out an issue I am having with my brand new MK3S and its linear bearings.

I got my new mk3s about two weeks ago, the build went smoothly I followed the instructions and read the online guide and also watched a few videos on the gotchas. I took me about 6-7 hours (I had some extra tools to help) and after running the wizard was ready to print. I printed a few small items off of the card with no issues, and was ready to print a benchy and up to that point was very impressed (coming from a few ender 3 frankenprinters) by the quality, then the issues started. During the print of the benchy I noticed an scraping/rattling sound which sounded like something was loose and rattling (metal to metal) so I cancelled that print (after checking the LCD) and set out to go over all the steps again. I narrowed it down to the two bearings on the left side of the Y carriage, so I loosened and hand tightened the holders, pulled the rods and packed the bearings, this helped but after a few more minutes the scraping would start again. I eventually moved those two and swapped them for two on the z axis and that helped, but the noise never went away. I also noticed that the Y carriage had a little bit of play, you could wiggle the frame about 1-2mm, which on the Ender 3 meant you did something wrong and needed to adjust something. I contacted support they sent me some new bearings and those were a lot better. Here is what I have found so far and I wonder if anyone else is having this issue.

  1.  The original bearings seem to be misumi bearings, they have made in Vietnam and a W/M logo on them, and have a part of LMU8. After looking online I found a match to the picture.
    1. If you run these bearing along a rod, you can feel a slight resistance like something is binding up, this also creates a vibration down the rod and if you put any pressure on it the vibration gets worse. I had assumed there should be no resistance and they should be perfectly smooth. (otherwise why even use them?) More grease does not seem to help.
    2. Some of the bearings work better in one orientation when they are aligned with the casing facing up, and with these if they are not aligned this way the vibration is much worse.
    3. Other bearings vibrate no matter what and you can hear a metallic scraping.
    4. And there are a couple of bearings that just scrape and feel gritty along the rod.
    5. I even soaked one with IPA and repacked with clean freshly opened grease and that didn't help.
  2. The new bearing have no markings on them and are much smoother but still feel like there is some resistance if just slight (I have checked the rods and cleaned them)
    1. They don't seem to have that same issue where it need to be perfectly aligned problem as the old ones.

 

I am in the process of printing and setting PLA versions of these bearings (with PTFE lube) which from my initial tests seem to work perfectly and super smooth, I also ordered a set of the polymer ones to see if they are any better. Has anyone else seen issues like this? Other than experimentation and trial and error I am not sure what else can be done. Is this normal for these bearings? 

Normally there should be no problems of this kind with Misumi linear bearings. Anyway, I have completely converted to slide bearings. On the Z-axis Drylin polymer bearings ( https://www.igus.at/product/1195 ) and on the X/Y axis slide bearings made of brass/graphite or sintered bronze. In the german forum there are some discussions about this. When using slide bearings, it is essential that the rods are well adjusted and aligned and that the distances between the rod axes are correct.

https://forum.prusaprinters.org/forum/original-prusa-i3-mk3-hilfe-zur-hardware-firmware-und-software/kreischender-drucker/#post-224229

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 11/07/2020 9:36 pm
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