X axis top rod damaged 2nd time.  

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cmc
 cmc
(@cmc)
Active Member

I have had a prusa mk3 printer for 5 months and about 400 running hours.

About 2 months ago i discovered damage on printer guide rod on X axis and figured that bearings can get damaged etc so ill just order new rods and bearings and swap them. This was done and i expected everything to be ok. 

Using new X axis rods I now have less than 30h of print time and all ready the top rod has gotten damaged.

Since print time is extremely small I am afraid there is something I am missing.

All replacement components are ordered from Prusa so whatever material issues are they should be managed by original manufacturer so i dont think this should be the problem.

Compared with the last time the rod got damaged, the location is 90' different. It was lubed well as can be seen from the image and also when doing assembly there were no bearing balls lost

Could anyone help me out to find the source of why my guide rods get damaged?

Posted : 10/03/2021 5:51 am
Diem
 Diem
(@diem)
Honorable Member

Is it only in the one spot?  I would expect a broken-bearing scrape to be longer ..?

Cheerio,

Posted : 10/03/2021 7:28 am
cmc
 cmc
(@cmc)
Active Member

@diem

The scrach mark runs for the most of the area my printer covered on last print. It comes and goes at spots.

Allthough when i think about it, the scratchmark looks different than last time, because it is not fully continuos as it has spots that are not damaged (yet) but generally covers the full range of motion.

My problem is that bearing is brand new and it would be a bit fast to start scraping. Also different from the last time is that i dont hear any noise from the bearing while at the last time it had some scraping sounds from time to time.

Posted : 10/03/2021 7:34 am
Clarmrrsn
(@clarmrrsn)
Honorable Member

Could this be a misprinted carriage?

Unlikely to be 2 sets of bearings bad, I would suspect the carriage case as well.  The part that holds the bearings.

Or rod holders? Can you measure rod spacing to see if even at both ends, maybe rods are not parallel?

This post was modified 3 months ago by Clarmrrsn
Tank you very much!...
Posted : 10/03/2021 9:20 am
Diem
 Diem
(@diem)
Honorable Member

@cmc

It does seem unreasonably unlucky (not impossible) to get the same rare issue twice in quick succession but this is the sort of damage that might be caused by one cracked ball in a linear bearing.

If this is the case it would be worth talking to Prusa chat (Log into your shop account, go to support, chat is at bottom right in most browsers.) and asking if they can think of an underlying cause.  They will want to see photos.

Cheerio,

Posted : 10/03/2021 3:06 pm
cmc
 cmc
(@cmc)
Active Member

@clarmrrsn

This is one of the possibilities. I do have Caliper to measure distance but i am not sure i can get reliable measurement of how parallel they are in the other axis.

I will look in to this.

Posted : 10/03/2021 5:13 pm
cmc
 cmc
(@cmc)
Active Member

@diem

It seems to be reasonable move to do. Thank you for suggestion.

Posted : 10/03/2021 5:14 pm
Clarmrrsn
(@clarmrrsn)
Honorable Member

@cmc

Any further with this?

My curiosity is getting the better of me.

Tank you very much!...
Posted : 13/03/2021 11:55 am
cmc
 cmc
(@cmc)
Active Member

@clarmrrsn

I have sent request to support but have not gotten any reply-s.

For now the plan is to Redo the cabling to have simpler access to the carriage/removal and i am ordering new guide rail and bearings again. This time i will also replace the parts holding on to the bearings to remove possibility that those are to blame.

Also i have an idea of doing a cleaning to the new bearings and implement more lubrication adding to there but since i have no idea what went wrong i just try things and see if anything goes better.

Posted : 13/03/2021 2:56 pm
Clarmrrsn
(@clarmrrsn)
Honorable Member

@cmc

Go onto the chat feature on the EStore (appears in bottom right on EStore page)

You will get a reply right away.

Far better than an email.

Tank you very much!...
Posted : 13/03/2021 5:20 pm
Clarmrrsn
(@clarmrrsn)
Honorable Member

@cmc

Sorry that should read EShop

Tank you very much!...
Posted : 13/03/2021 5:26 pm
MrBleadd
(@mrbleadd)
Active Member

Today the same happened to me too.

Just a normal print, then suddenly I heard a scratching noise. I checked the upper X-Rod while printing and saw a small scratch mark, about 5 mm wide. This already happened to me once, the support was very nice and sent me a replacement. Since then I took extra care of this upper rod, it still happened tho(after 300 hours of printing). I don't know what I did wrong. I did regular cleaning and greasing of the rods.

Now I am thinking about using a linear Rail instead of replacing the upper rod with a new rod again. I don't wanna deal with that again. I know from work that linear Rails are not easy to destroy, they run 24/7 the whole year. just a bit of grease now and then. 

These would be the mods:

X-Axis mod: https://www.prusaprinters.org/prints/16838-prusa-mk3-mk3s-mk3s-x-axis-linear-rail-guide-upgra

Y-Axis mod: https://www.prusaprinters.org/prints/5620-prusa-mk3-mk3s-y-axis-linear-rail-guide-upgrade

What are your thoughts?

Posted : 16/05/2021 6:58 pm
JoanTabb
(@joantabb)
Moderator

@mrbleadd

Tom Sanladerer did a similar upgrade, he was not impressed, he believed that the rails over constrained the axis... 
might be worth watching the video on Youtube!

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 16/05/2021 7:45 pm
--
 --
(@)
Illustrious Member

The first question I have to ask is if the bearings were cleaned and degreased before adding lubrication.  If these are typical Chinese bearings, they come filled with machining debris and not cleaned and washed. 

Posted : 16/05/2021 8:00 pm
MrBleadd
(@mrbleadd)
Active Member

@tim-2

Prusa shipped me some with the new rods. I degreased them and filled them with grease (from Prusa), removed the excess grease.

@joantabb

Yeah I have seen his video, the Y-Axis is not a problem for me. I just like the looks of it. The X-Axis is the real problem, that is why I want to do the mod, replace the upper X-Axis Rod with a linear rail. 

Posted : 16/05/2021 9:14 pm
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 --
(@)
Illustrious Member

@mrbleadd

Over tightening the extruder case will crush the linear bushings and cause them to seize. That is about the only thing  - besides not cleaning them properly - that will cause them to fail prematurely. 

The bearings will last a long time if installed properly. They can carry the load of the X and Y axis with ease.

ps: there is one design flaw in the extruder - if the end supports are not printed to match the extruder - the rods will be deflected as the extruder moves back and forth, this can place undue stress on the bearings and destroy them. Black residue on the shafts in a sign of this (rubber seals are abrading).

This post was modified 1 month ago by --
Posted : 16/05/2021 9:30 pm
MrBleadd
(@mrbleadd)
Active Member

Yeah that is what I also found after searching through the forum. I loosened the screws an rotated the rod. Now the screws are just touching the backplate with just a little pressure on the bearings.

Let’s hope I didn’t crushed too much, they have to survive at least a couple of print, I need to print some stuff for university. Really bad timing I would say 😛

 

but the X-Axis mod still looks interesting to me. 

Posted : 16/05/2021 9:44 pm
MrBleadd
(@mrbleadd)
Active Member

@tim-2

There is actually always a bit grayish  black residue 

Posted : 16/05/2021 9:46 pm
MrBleadd
(@mrbleadd)
Active Member

@tim-2

So it should be good to check if that’s the case (if I have the problem caused by the design flaw). 
Thank you very much ^.^

Posted : 17/05/2021 7:25 am
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 --
(@)
Illustrious Member

@mrbleadd

If you look at the X support brackets, they are printed in orange on a printer. The profile is that the center distance of the rods is set by the Z -axis. Fairly accurate machined interface. The extruder is printed in black on another printer, but the rod spacing is based on the printer's X or Y calibration, which is not nearly as accurate as Z. Plus, the buildup is not layers, but an extruded length: shrinkage is different. If a person is lucky, the extruder comes off a well calibrated printer. If unlucky, you get a major undersized case that causes problems.

If you clamp the extruder down onto the bearing so it fits into the recess available in an undersized case, it will compress the upper and lower bearings and seals between the the rods. The issue is the rod spacing is wrong - not the bearing diameter. This is one reason why releasing the extruder case screws will help reduce drag on Mk3S printers - it allows a bit of space for the bearing to ride up out of the case and move closer to the ideal rod spacing.

The first sign the of excessive wear is the seals abrade and the black dust from them fills the grease leaking from the seals leaving that grey-black oil film.

You can measure for this easily: Measure rod to rod at both ends of the X-Axis, then with the extruder in the middle of travel, measure the rod spacing next to the extruder bearings.  The bearings are spec'd with a 8.000 mm 0/-0.009 mm tolerance. So any rod deviation from true (all three measurements equal and exact) can't exceed 0.009 mm or the bearing will wear abnormally.

This post was modified 1 month ago 2 times by --
Posted : 17/05/2021 7:43 am
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