failed bearings again MK3S  

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marzubus
(@marzubus)
New Member

I am on my second failed linear rod and bearing. There are deep scores in my upper linear rod and I can hear there is grinding. This is the 2nd bearing failure in under 40 hours of print, resulting in linear rod damage.

I greased the current bearing before installation according to https://prusacommunity.com/set-your-bearing-straight/ , with the included grease which came with the printer.  And it didn't last 40 hours before grinding.

Either the grease is not right, or the bearing and linear rod materials are poor / not matched in terms of hardness. So I am looking for alternatives. I have some Mitsumi linear bearings, but cant find information as to what hardness linear rods to match with them.

Has anyone with similar issues and replace the stock bearings with Mitsumi with success?

Posted : 07/09/2019 11:09 am
Robert-mm200
(@robert-rmm200)
Noble Member

Upper linear rod? X Axis?

I would suspect you are crushing the bearings. Loosen the screws in the extruder cover a bit.

Posted : 07/09/2019 10:15 pm
Tim
(@tim-m30)
Illustrious Member

The extruder can compress/bend the X-Axis rods due to plastic variation. This makes motion problematic and wears bearings.  Especially if you printed your own parts and didn't verify they meet the drawing specs.   Also, the bearings need to be cleaned then packed with grease. A dab of grease on the rod is not enough.  The community article has most of the bits right but I challenge the assertion Prusa bearings come with synthetic oil with PTFE; nor do they come pre-cleaned of machining bits.  My new Prusa kit bearings sounded like they had sand in them and were ruined along with the rods on the first print (yes, they got me the first time, too).  Replaced them with Misumi bearings, properly greased, they lasted longer, but on stock rods were loose to start.

Y-Axis bearing clamps - the U-bolt method - are way too easy to over tighten and damage the bearings.  I only go finger tight with mine.  Next set of bearings (already here) will use homegrown plastic holders. 

My impression (data set of 1 of 3) is using the Belt Tension numbers, try to get motion to be a frictionless as possible: numbers of 300 being the goal.  And yes, you can get close to 300 and have tight belts.

 

This post was modified 1 year ago by Tim
It is always wise to get more than one opinion......
Posted : 08/09/2019 3:22 am
marzubus
(@marzubus)
New Member

I am 100% certain nothing is over tightened.  And I have degreased and greased bearings very thoroughly.

My carriage parts were printed by Prusa, so if there is spec issues, I cannot know.  

Also belt tensions are ~290, So it’s on the looser end already.

i will order some mitsumi rods from UK.

Posted : 08/09/2019 7:09 am
andy.b17
(@andy-b17)
Eminent Member

I have the same on a 4 month old printer - Contacted Prusa last night and they are sending out 5 replacements!!

Posted : 09/09/2019 3:51 pm
Tim
(@tim-m30)
Illustrious Member
Posted by: andy.b17

I have the same on a 4 month old printer - Contacted Prusa last night and they are sending out 5 replacements!!

5 bearings for a 10 bearing system ... cool; especially when you need a minimum of 6 for the two horizontal axes.

It is always wise to get more than one opinion......
Posted : 09/09/2019 8:17 pm
Robert-mm200
(@robert-rmm200)
Noble Member

I would not expect them to replace more than the damaged parts...

Posted : 09/09/2019 8:31 pm
andy.b17
(@andy-b17)
Eminent Member

I know i was asked if it was one or two x bearings that failed and as I couldn't be sure if one or both were at fault the support guy said he will send 5 🙂 the Prusa support is amazing.

 

Shame it hasn't helped my regular jams and blockages.

Posted : 09/09/2019 8:36 pm
Tim
(@tim-m30)
Illustrious Member

Well - maybe they are getting better - they just laughed when I asked about my shot bearings at 3 months.  Same for the heavily scratched PEI sheet and a bad spool of filament (only 5% of the filament was shot, but it was a serious waste of time, effort, and source of much frustration).  

It is always wise to get more than one opinion......
Posted : 10/09/2019 12:07 am
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