Can't get the filament blades to stay in place
 
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wdgeek
(@wdgeek)
Eminent Member
Can't get the filament blades to stay in place

Have been trying for the past two weeks to get the 2 blades that are used to cut the filament to stay installed. After using the MMU3 for a while eventually the blades would fall out of the holder and cause problems. I have tried a half dozen times to reinstall the blades but despite really tightening the screw that holds the blades in place to the point that I'm afraid I will break a part, the blades just will not stay in the holder and would eventually fall off and jam the MMU3. I eventually just took them out to avoid having a failure due to the blades falling off.

Has anyone been able to successfully install the blades without them falling off the holder? Seems like this is a design failure. 

BTW, when the blades were installed and working, they seemed to work well to "cut" the occasional "string" of filament just due to the back-and-forth movement of the MMU3 when changing filaments. 

Posted : 14/11/2023 8:37 pm
3Delight
(@3delight)
Moderator Moderator
RE: Can't get the filament blades to stay in place

No problems like that here.  Though I did have to shave a little bit off of the selector body to allow them to fit in the recess... The tolerances are very tight.

Posted : 14/11/2023 8:48 pm
wdgeek
(@wdgeek)
Eminent Member
Topic starter answered:
RE: Can't get the filament blades to stay in place

Are you saying that by "shaving the selector body" you mean that you made the "recess" where the blades fit, "deeper"? When I installed the blades, they seemed to fit perfectly, but I suppose by making the recess deeper it would help keep the blades from "slipping" out of the recess. If that is what you did then maybe I should try that.

Posted : 14/11/2023 10:09 pm
3Delight
(@3delight)
Moderator Moderator
RE: Can't get the filament blades to stay in place

Not deeper, but wider as the blades were pushing too hard against each other causing them to bow upwards and fall out.  This bowing also prevented the cover from being tightened sufficiently to hold them in.  This may not apply to your scenario but take a good look at how well they fit in the recess and whether trimming it would help them fit.

Posted : 14/11/2023 10:12 pm
wdgeek
(@wdgeek)
Eminent Member
Topic starter answered:
RE: Can't get the filament blades to stay in place

My experience was different. As far as I remember the two blades fit perfectly into the space provided. The blades were flat and the blade cover seemed to fit properly when tightening back down. I will check your suggestion and if the blades fit properly I think I will try to make the recess slightly deeper to see if that would help keep the blades in position without sliding/slipping off. Thanks for the information. Next time I feel like dealing with the blades I will try to see if a deeper recess will help.

Posted : 15/11/2023 5:14 am
Thejiral
(@thejiral)
Prominent Member
RE: Can't get the filament blades to stay in place

I don't know if the MMU3 blade mount differs much from the MMU2 but I simply removed the blades altogether, after they made more troubles than they are worth. They are designed against stringing rather than cutting solid filament. However for reliable operation one should aim for stringing free filament exchange anyway. Once there are strings appearing, things usually get messed up rather sooner than later anyway, blade or no blade. 

Mk3s MMU2s, Voron 0.1, Voron 2.4

Posted : 15/11/2023 7:39 am
wdgeek
(@wdgeek)
Eminent Member
Topic starter answered:
RE:

Yes, I completely agree. String free filament tips are the preferred solution. I print with Overture PETG exclusively. I've found that tips from the Overture PETG seems to vary. Sometimes they are horrible and sometimes they are perfect. I have not been able to figure out how to get them consistently string free. (close but not consistent).  In any case my short-term solution (which might turn out to be permanent) is to take out the blades. Printer still works well without the blades. When I was running the MMU2, I could never get consistent results, so I was just using it as an easy way to change the filament to one of the five colors. And even then, it would sometime be super frustrating with jams and errors. Never could ever print any multicolor print of any complexity until I tried again with the MMU3. I was able to print several multicolor prints (Multcolor benchy, muticolor lizard) but the blades dislodging really caused a lot of problems. I am currently using a REVO ObXidian nozzle with the MMU3 and it works well so far. I tried using the blades with the MMU2 but it never worked, so I never used them. I just figured with the new design of the MMU3 Prusa would have improved the knife system. I guess that is not the case.

This post was modified 3 months ago by wdgeek
Posted : 15/11/2023 9:23 am
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