Hello everyone,
after much experimenting, I have drawn some conclusions about bridge management by Slic3r, that I would like to share to gather other users' feedback.
My setup: Prusa Mendel, K extruder, Melzi board with Sprinter firmware (the kit assembled by Heacent). Printing in ABS, 0.15 mm layer height with 0.3 mm nozzle, 240 degrees for all layers (use less and bridges will be damaged by subsequent nozzle passes, use more and the filament will soften, the extruder gear will dig a notch in it, and printing will stop). Using Slic3r 1.0RC2.
First thing I noted is that when drawing bridges Slic3r seems not to take into account that the layer height is not the same as in other conditions, since there is no material to spread it upon. Maybe I noticed this because I am using layers much thinner than the nozzle opening. In practice, bridges will snap unless I set an insane flow rate multiplier (at least 2.5, 3 works best). Anybody noticed this?
Secondly, it looks like that, when covering an infill area (in my case honeycomb), Slic3r correctly recognizes the area as a bridge area and sets the correct flow rate and activates the fan. But fails to use the (in my case slower) bridge speed, extruding instead at infill rate. This means that, due to the huge multiplier, lots of plastic are extruded, requiring a great amount of energy and potentially leading to hot end cooldown because of slow response of the PID controller, and thence filament block, notching and failed print. Or, if the printing goes through, at the end of the bridge layer (also due to PID inertia) temperature rises, exceeds 300 degrees, the idiot firmware shuts down the hot end and does not turn it back on when temperature drops, so again failed print.
Anybody can confirm this?
Edited 1 time(s). Last edit at 02/18/2014 04:27PM by jameson.