MMU2 Cutter  

Re: MMU2 Cutter

I am not sure. When I look at some of my stringy filament, I have sometimes tried to think whether a cutter would help. This may have raised the idea of putting it on at Prusa.

I've come to the conclusion it wouldn't help me. If I'm not getting stringing, it isn't needed, and would actually likely be counter productive, as the nozzle withdrawn tip with the slight point is actually better for loading that a straight cut with sharp edges. If I *am* getting stringing, I don't think it would help much. If there is a string, it can potentially stay in the finda on unload, causing the filament to be over-withdrawn. Cutting at that point could potentially trim the tip of the string, but the damage is done.

Re: MMU2 Cutter

Unless a cutter was implemented at the extruder so zero retraction was required, just purge the extruder length of filament, there's no real benefit of the cutter. The filament tips and strings are whats holding everyone back from perfect prints and a cutter at the mmu unit does nothing to help those issues. The purge would be greater with an extruder area cutter but think of all the wasted filament in failed prints so far... I can't even imagine how much has been thrown away due to stringing and/or bad tips.

Re: MMU2 Cutter

I am really thinking that a cutter in the extruder area is a great idea and I would like to explore it. It would remove the unreliable ramming for all types of filaments and you would won the time associated.

The cutting blade would be between bondtech and E3D, like 65mm above the nozzle output (see picture below).

The things would be as follow:

- Printing with filament 1
- Stop extruding and retract 55mm of filament
- Moving to the purge bloc
- Perform cut, about 10 mm of filament 1 still in the extruder (amount to optimize to minimize purge)
- Retract filament 1 to the MMU
- Load filament 2
- Purge colors
- Print with filament 2

The filament is not so easy to cut, I tried on a table with a cutter by just applying a pure vertical force and you need a huge force, I think that a circular blade mounted on an excentric could do it easier with a little servo motor.
Whatever the PALETTE+ does it well and reliably, does anyone know how it works ? any picture ?

Does anyone see something really stupid about this idea ?

If not I'm ready to make tries on it

Re: MMU2 Cutter

Very interesting concept.

I just implemented the cutting in the MMU2 firmware rewrite if anyone is interested.

so far it is working great at cutting off a dodgy tip from a previous unload.

https://shop.prusa3d.com/forum/general-discussion-announcements-and-releases-f53/improvements-to-the-mmu-2-0-controller-firmware-t25189-s50.html

Rob

Re: MMU2 Cutter

A little bit of ignorance on my part but...Where does the piece that is cut off go? I haven't received my MMU to MMUV2 upgrade yet and have been wondering.

Thanks,

Neal

Re: MMU2 Cutter

I actually removed my cutter because it somehow got knocked and was digging into the plastic causing me to not be able to change filaments past #2. Haven't had problems moving between filaments in Single mode since (still experiencing ALL the other MMU problems though.)

Oh... and if you do this be extremely careful taking apart the MMU to that point. I saw that mine was hanging up, so opened to investigate and forgot about the cutter and sliced my finger. Not terribly bad, but just be careful.

Re: MMU2 Cutter

A little bit of ignorance on my part but...Where does the piece that is cut off go? I haven't received my MMU to MMUV2 upgrade yet and have been wondering.

Thanks,

Neal

This. Current users would know if the cutter is being used or not as there would be cut-offs in the MMU 'trough'....

Texy

Re: MMU2 Cutter

I also removed my cutting blade as it keeps comming out and jamming.

Re: MMU2 Cutter

A little bit of ignorance on my part but...Where does the piece that is cut off go? I haven't received my MMU to MMUV2 upgrade yet and have been wondering.

Thanks,

Neal

I'd like to know this too..

RE: MMU2 Cutter / Stainley Klinge

Hi, my cutter sits in a loose position and is of no use. it can't be placed in a stable position. any ideas?  currently I have removed it. 

MK3s/MMU2S - Dec. 2019 manufactured

RE: MMU2 Cutter

My cutter blade would occasional "catch" filament and pull it into the next tool position. This would cause the selector to jam. Then requiring the removal of the three screws holding the selector motor so I could remove the offending filament.

After the blade fell out mid print, I never reinstalled it. Have not had a related issue since. Other MMU issues yes, but not related to selector jams.

RE: MMU2 Cutter

the cutter can never be not enabled as its in a fixed position, any move of the selector in one direction will always cut whatever is in its path which should only be strings of filament that didnt create a nice tip.

RE: MMU2 Cutter

@jesse-hauf

I found it easier to clear jams due to the cutter dragging filament by releasing the lock nut attached to the selector (2 screws) that allows you to slide the selector along the shafts. Then use an allen key and needle nose pliers to clear the jam.

RE: MMU2 Cutter

In the 3.9.0 RC1 firmware I ran across a menu option to enable the MMU2 cutter. And on github there are revised MMU2 parts for the blade holder that holds the blade at a different angle. I printed and installed the revised parts but I haven't tried the new firmware switch yet. 

RE: MMU2 Cutter

Cutter works with 3.9.0 rc1 with little modification, I've tested it.

https://forum.prusa3d.com/forum/original-prusa-i3-mmu2s-mmu2-hardware-firmware-and-software-help/anyone-using-3-9-0-beta-firmware/