I finally got around to trying the 0.75mm nozzle on my Metal Plus. It arrived before the holiday, but I didn’t have the time to make a custom wrench for it (the flats appear to be just a hair too far apart for the quarter-inch open-end wrench I got at the hardware store).
It produces a better texture on t-glase than the 0.4mm nozzle, and it prints way faster (more than doubling the layer height will do that). The lower resolution doesn’t matter for a lot of prints — like this battery-enabled bumper for an arduino clone.
But. The PID parameters for the hot end definitely don’t have this nozzle in mind. Printing at full speed, temp was consistently 15C below setpoint (and that print eventually died with adhesion problems). I knocked back my printing speed by about 25% and got a print with the hot end only down by 7C. (In vase mode, where extrusion is even slower, the temperature was dead on. Go figure.)
It’s clearly not about whether the heater can keep up with the needs of the bigger nozzle (see where the temperature heads back up after dropping when serious extrusion starts). The algorithm simply has certain expectations about how much heat it has to pump into the hot end for a certain temperature increase, and they’re not being met. As the prints went forward, I could see the temperature going back up a few degrees, the PID backing off the heating rate so as not to overshoot, temp going down, repeat…
Given the big discrepancy, the dependence on flow rate, and the fact that I’m not going to be using the big nozzle all that often, I wonder whether I should spend a lot of time on tuning or just crank up the target temperatures when I need to. Any other big-nozzle dilettantes out there?