3DPrinting
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I don't see the full reason anywhere in the thread; the prime tower is essential to quality multicolour prints. Purging quickly shoots out a high volume of filament to quickly clear as much of the previous colour as possible, but then when it goes to start printing, the temperature and pressure are all out of whack and you get inconsistent flow.
So, if you skip the prime tower, you'll get globby over extrusions and gaps from under extrusion on the first thing printed in that colour each layer, which looks terrible.
That said, the prime tower can be much smaller than default. I set mine to 3mm³ of priming and it comes out 95-100% perfect, with only very occasional blobs on the edge, which pop right off with a fingernail flick (or a deburring tool, if you're fancy.)
Don't skip the prime tower. I did for a few weeks before cluing in to why I was getting 1 bad print on every plate.
I suppose if you're changing filament by layer, then you could maybe skip it, but then definitely don't print outer wall first or you won't get a clean print. But even then, a 3mm³ prime tower is tiny, so why risk it?
Hell, even the Snapmaker U1 uses a prime tower, and it has 4 hot ends; it's needed to normalize the flow after a temperature/flow change (being idle). I don't have one to test, but I expect it would greatly benefit from a bigger prime tower, since it hasn't just been extruding filament as purge to get things flowing. But that's just speculation, as I sadly don't have one to test with.
I have a U1 which is what prompted this post. But Snapmaker doesn't "use" a Prime tower. They took Orca and kept all the defaults. I was thinking that they might have intentionally kept the prime tower default because they don't have a real poop chute but only a poop bin which would quickly overflow if they primed into it.
I don't have one, but I expect they kept that default setting for the reasons outlined above, but because of a lack of poop chute.
I have a Creality Hi, and a 3D-printed poop chute off the side of the printer holds plenty of poop for typically-sized 4-colour full-purge prints.
For really huge prints, I empty once mid print, but those prints last for days anyway, so it's no big deal.
With no need for colour/material purging, I would expect a purge tray to be plenty for a multi-toolhead printer. I can't imagine it purges much?
The prime tower probably could be much smaller. Its size is mainly structural so that on a tall print it stays stable. But the poop tray on the U1 is pretty small. I could see it needing to be emptied after every large multi color print if it primed into the poop tray.
I suppose that makes sense. I almost entirely print short things, and when I do taller prints, it's always single colour because it's a functional piece.
I'm not interested in giant 3D print display art, personally, so I've never run into that challenge. Hell, I set my prime tower brims to 0 just to make it easier to get off the plate.