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End of tether finally reached....  

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AndyInSwindon
(@andyinswindon)
Trusted Member
End of tether finally reached....

So, a 35hr print, started on Thursday evening, expected to finish last night.  Woke up this morning to find the printer bleating for attention, MMU2S requires user attention blah blah.

When I had left the printer before going to bed, there was around an hour left to print.  I examined the MMU2S - no fault found, reset it (as in primed it ready to continue), at which point it stated that the print was finished, 100%, despite it clearly not being the case.

Having wasted half a reel of filament, and many many hours on this print, the MMU2S is coming off.  I need a functioning printer that I can rely on.  If the MMU2S can't even cope with single filament mode, I'm no longer wasting my time.  I have a door that needs propping open, I can use it for that.  I am running a business, not a satellite R&D lab.  £10 of filament down the drain. 

I know that this sounds harsh, on another forum in the early days, when I asked about MMU2S issues, my mental capacity and parentage were questioned.  However, when you buy a car, you expect to drive it off the forecourt, not have to tinker around with the engine and fuel to get it to work.  And when it gets you 10 miles from home and breaks down, and the gps insists you're home.....!

No, I'm not selling it.  That always seems to be the answer from many.  However, this has now become far too tedious.  It took me 35hrs to print a 5 colour benchy last week.  Really?  35hrs?  Who has that much time on their hands!!!

This is probably more of a rant and a report on my experiences with the MMU2S than a query for technical help.  So I apologise if this offends anyone, it's really not the intention.  And if you have read this far, thanks for sticking with it. 

Posted : 25/01/2020 9:41 am
AndyInSwindon
(@andyinswindon)
Trusted Member
Topic starter answered:
RE: End of tether finally reached....

Ok, time to swallow a bit of pride/humility on this one.  I've just stripped down my Mk3S to remove the troublesome MMU2S unit.  Whilst removing the bondtech cover in order to swap it back, I have found the bondtech gear bearings to be seized.  So whilst it isn't an MMU2S fault per se, it's still galling that the print failed so close to the end of a 35hr print.  And really? £35 for a bondtech set from Prusa?  All I need are the needle bearings. 

Question is, what has caused them to fail :-

1. Lengthy print time?  (Unlikely)

2. Differential in feed speed from MMU2S and take up speed from extruder placing extra stress on the bearings? (also unlikely)

3. Poor quality needle bearings?

4. Idler tensioned too high? (Maybe)

Still, a frustrating and expensive resolution regardless.

Anyone else seen these fail?

 

Posted : 25/01/2020 1:54 pm
vintagepc
(@vintagepc)
Member
RE: End of tether finally reached....

Why were they seized? Were they full of junk (e.g. filament dust?) or did the plastic cage crack?

Lack of lubrication?

One possible contributor is the metal rod in the door has a tendency to come unmounted on one side; this causes the door side to sit at an angle, uneven loading will very likely kill a bearing in short order.

Posted : 25/01/2020 3:21 pm
AndyInSwindon
(@andyinswindon)
Trusted Member
Topic starter answered:
RE: End of tether finally reached....

@vintagepc

Hi vintagepc,

plastic casing was fine, shaft was in place, and bearings were lubricated when assembled - and this machine has far fewer hours than my other unit.

Still, lesson learned, just another item to throw into the mix, and I am going to find a supplier for the needle bearings.  I appreciate that Prusa sell the entire kit, but the gears are absolutely fine.  I don't need the whole thing.

Posted : 25/01/2020 4:34 pm
AndyInSwindon
(@andyinswindon)
Trusted Member
Topic starter answered:
RE: End of tether finally reached....

...just had a look at the needle bearings on my other Mk3S.  It has 58 days of print time, 2.5km of filament, and the Bondtechs look as good as the day they were installed, and the bearings run beautifully.  Compared to the Mk3S with the MMU2S installed, which has about 1/3 of that usage, it's night and day.  Has anyone noticed extra wear on Bondtechs with MMU2S units installed in comparison with single filament systems?  It would stand to reason that the MMU2S units do get extra abuse due to increased load / unload operations rather than just spinning happily in one direction for hours on end.

 

Posted : 25/01/2020 4:55 pm
vintagepc
(@vintagepc)
Member
RE: End of tether finally reached....

I have an MMU2S, have done quite a few prints on it and have noticed no issues. All was well when I recently rebuilt my skelestruder after some maintenance.

Posted : 25/01/2020 5:17 pm
Ken G.
(@ken-g)
Eminent Member
RE: End of tether finally reached....

So far my needle bearings look good and I don't have excessive wear, I did make a couple of changes to the MMU, but I suspect most people have by now. I changed out the plate where the FTFE tubes come in with pass through adapters so the tubes will no longer get pinched. I also replace the PTFE tubes with larger internal diameter tubes.

 

My MMU has been working for a bit with no issues. I probably should not tempt fate like that tho.

Posted : 26/01/2020 3:24 pm
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