Use Case:
I am printing with PLA in extruder 0 and PVA in extruder 1. I have my retraction settings working quite well and I'm using a combination of a skirt and the prime tower to guarantee the first layer of the prime tower is fully extruded. I don't need much of a prime tower. My smaller prints get by fine with a prime tower that's only 6-8mm wide.
However, PVA is sort of brittle and weak compared to other materials. And as such, when the prime tower gets taller, the tiniest lateral friction applied to the top layer by a passing extruder nozzle or dragged oozing filament, results in significantly higher and higher torque applied to the bottom of the tower, as it grows taller. Eventually, it snaps near the bottom and after that, the print usually fails, due to the strings that fall from the now vacant tower area building up chaotically enough to cause other problems. As I have good adhesion, the break is usually a few layers up rather than from the bed itself. One might imagine that even a solid PLA tower might eventually fail at the bed, with a tall enough tower, as found in modern printers with big Z axes.
I can print a wider tower to get wider base layers that will better withstand torqing from lateral friction higher up on the tower. However, the amount of filament that it takes to fill in such a tower makes such a solution cost prohibitive, slower to print, and is less than ideal. And really, I don't need to prime THAT much filament. Certainly not higher up on the tower. Again, I get along fine with a 6mm tower for actual priming purposes.
Not so great alternative:
I can use an ooze shield instead which doesn't suffer the same geometric torque in most cases. However, the ooze shield changes the amount of filament that is primed based on the shape of the print at any given height. Whereas the prime tower is constant. The prime tower is a better solution for priming. And the ooze shield is a better solution for, shielding from ooze. I should not be using an ooze shield as a prime tower.
Failed Approach:
I tried using multiple processes at different heights (both with the wizard and manually) to get a tapered tower. However, the tower width doesn't seem to respond to such a change properly. (v4.0.1)
Feature Request:
I'd like to be able to specify the infill density of the tower, such that I can specify a wider tower when I need to make it wide, to withstand torqueing; and can reduce the infill so as to avoid wasting too much filament on its interior, while getting the benefit of the better geometric distribution of forces to the base.
Additional Idea:
It might be even better to be able to specify both widths and infill density at different heights, such that I can specify a base that tapers in and out and becomes more or less dense as I deem neccesary. That way, I can try and find an ideal tower footprint and desnsity profile for whatever filament combination I'm using.
Additional Idea:
It might be better to be able to choose a different shapes for the tower, that can better brace it from more angles. For example, an N-pointed star which would result in wider radial fins around a core. Or a cylinder?
Additional Idea:
The same kind of sequential infill angles control I get on the support might be useful here. For example, I use 0,45,90,45 to keep my support building triangular lattice to get better bracing in arbitrary directions. The existing tower seems to go 45,-45 which means the lattice is orthogonal and could be weak in some cases.
Re: prime tower infill setting
No answer yet... Mmmm.
I've got the very same issue as you. Once colours start switching, It starts building this huge blog on one corner, until it gets big enough to offer resistance to the nozzle, and then, eventually, break the tower at the weakest point which was, for me, printing the benchy, around 6mm high where colours start to mix. I combined the wall AND the prime tower, because I believe they are complementary, one ensure oozing control, the second ensure colour transition. But yet it broke. The part itself got quite a decent result (up to the break point when it goes Armageddon.
I tried random starting points but they apparently don't apply to the prime tower. Until I moved it from north-east to north. Then I managed to have the prime starting points distributed between two corners. I'm going to try. It might be just enough to prevent the accumulation effect.
If that fails, I dont know what to do next.
I've got the very same issue as you. Once colours start switching, It starts building this huge blog on one corner, until it gets big enough to offer resistance to the nozzle, and then, eventually, break the tower at the weakest point which was, for me, printing the benchy, around 6mm high where colours start to mix. I combined the wall AND the prime tower, because I believe they are complementary, one ensure oozing control, the second ensure colour transition. But yet it broke. The part itself got quite a decent result (up to the break point when it goes Armageddon.
I tried random starting points but they apparently don't apply to the prime tower. Until I moved it from north-east to north. Then I managed to have the prime starting points distributed between two corners. I'm going to try. It might be just enough to prevent the accumulation effect.
If that fails, I dont know what to do next.
