Pause for filament chanage behavior
I frequently print two-color models where the printer pauses between layers for me to change filament. When I do this, I have the following observations/dislikes:
1) mid-print changes provide a "Purge More" as an option, and I frequently need to do this. But unlike a normal filament change, I don't have option to say "Stop", it's now good. Would be great if it worked just like extra-job filament change.
2) When I do finally say the color is correct, it squirts out another. ~2 cm of filament that just dangles from the head. Always a waste, and sometimes it causes problems with the print or is left "hanging off". I have to grab it with a pair of needle-nose from a moving target. I don't see a need for this, so can't we get rid of it?
RE: Pause for filament chanage behavior
All reasonable suggestions but this is a user-to-user self-help forum, and Prusa devs are not known to hang out here. If you want to get your ideas in front of Prusa eyes, you're better off creating an "issue" on their Github site: https://github.com/prusa3d/Prusa-Firmware-Buddy
Formerly known on this forum as @fuchsr -- until all hell broke loose with the forum software...
RE:
That extra purge of filament is so that you don't end up with a spot of no extrusion on your part. You'll notice that after the purge even when the extruder stops the filament keeps oozing. This will lead to a void in the extrusion on your part. Therefore after you say it's good it'll push out a little more to make sure the nozzle is completely primed.
All you need to do is have a wire brush in hand under the nozzle and when you click ok it'll purge into your brush and then off it'll go with nothing dangling.
Another option is to use a purge tower. Then after the filament change it'll go over to the purge tower before going back to your part.
So in a nutshell that extra little purge is needed unless your ok with a small gap of no extrusion on your part.
You can see what this gap would look by pausing your print. The nozzle will park and continue to ooze after the pause. After you hit resume if you watch closely you'll see that when your extruder returns to your part it will travel a small distance and nothing will come out of the nozzle. This is the exact reason I recommend if you ever need to pause a print, do it during infill.
You can also see this when the nozzle prints the purge line at the beginning of the print. If you notice it always travels a small distance before filament starts coming out. This is not because the extruder is not moving, it's because the nozzle is not primed. The effect of this is worse on filaments like TPU and PETG which tends to ooze more than PLA, however it still happens.
RE: Pause for filament chanage behavior
The other thing is that neither of those points have anything to do with Prusa slicer. Those are both determined by the firmware in the printer. All the slicer does is command the filament change. Once it’s started the mechanism the printer follows to archive this such as purge lengths etc are up to it.