Filament brake suggestion
Hello all,
first of all - I'm completely new here, and not even yet new to 3d printing (just preparing what I intend to become the work area, reading up on Stuva enclosures and air filters,...), so if any of this is out of line, be sure to tell me.
But one of the main reasons why I'm planning for an i3 Mk3 was the MMU. Now I'm reading here that several(?) of the people who already have their MMUv2 operating seem to have problems that relate to the fact that this MMU has to push back the filament towards the spool when switching colours. For this, PR is suggesting a highly specific spool placement (which a lot of people, me included, simply don't have the room for) and a simple filament brake. I haven't been able to see anyting specific about this brake yet, but from the pictures I've seen here on the forum, it looks very simple indeed (KISS).
Idly thinking about this while waiting for my bus: how about a slightly more involved filament brake that would offer little to no resistance when pulling the filament, but high to very high resistance to pushing it back? Not strictly KISS, but could open up a lot of room for the filament routing. Basic idea would be something along a roller clutch/one way bearing/sprag clutch (on thingiverse), or like a specific type of clam cleat (Curryklemme in German, 
). As I'm not a mechanical engineer, I think you lot can come up with a simpler and better design for that - and hopefully something that is cheaper than a couple of bondtech gears on a roller clutch.
Hope you get this solved by the time I get my MMU 😉
Re: Filament break suggestion
But one of the main reasons why I'm planning for an i3 Mk3 was the MMU. Now I'm reading here that several(?) of the people who already have their MMUv2 operating seem to have problems that relate to the fact that this MMU has to push back the filament towards the spool when switching colours. For this, PR is suggesting a highly specific spool placement (which a lot of people, me included, simply don't have the room for) and a simple filament brake. I haven't been able to see anyting specific about this brake yet, but from the pictures I've seen here on the forum, it looks very simple indeed
The main problem the Prusa filament holders are solving is making sure that the filament doesn't tangle when it unloads. You don't want a lot of resistance when unloading the filament (in fact, you want as little resistance as possible).
The purpose of the brake is to keep the loop of filament from backing over the spool and possibly forming a knot. Instead it forms a loop in front of the brake, where it's less likely to tangle.
The actual placement of the filament spools isn't as critical as some of the early comments seemed to suggest. But the general advice is to get your MMU working with the recommended spool placement first, before you try changing things. That's because there are so many variables with the MMU that troubleshooting is a challenge, and it's best to start from a configuration that's known to work.
Re: Filament break suggestion
I think those cams (makes nostalgic for my sailing days) would be very effective at preventing pushback into the spool.
The other half of the equation is controlling where the pushed back filament goes. If it slides up relative to the cam, it'll break the braking effect. If it loops sideways, you'd need to make sure it doesn't catch on something, and when it gets pulled back in, avoid kinking the filament.
I like this approach, mostly because it looks cool: cool filament brake/guide
Re: Filament break suggestion
Ok, you (ok, TheBall) win. That looks both simpler and more reliable than anything idling around in my head right now.
Plus the idea of mounting the MMU inside/between the dry box and the printer box 😮
Re: Filament brake suggestion
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Thomas