Extruder "Retract amount before wipe"-option and underextrusion
Some info to begin with:
I have a Prusa MK2.5S + MMU2S and I do multicolor prints occasionally. I have been using my own post-processor (filaswitch) to add the tool change gcode since it has been more reliable than what PrusaSlicer does, although last time I tried PS MMU handling, it worked ok for a short print.
About a year ago I noticed that I got some quite severe underextrusion in some parts of the models; some paths started 'late'. At that time I tuned some settings (Retract amount before wipe was one) and got rid of the problem, until I tuned this setting again few days ago. Basically changing the RABW from default 0% t0 something like 60% fixed this issue completely.
Here's couple of pictures of the problem. From left to right: single color print, dual color print with RABW 80% and dual color print with RABW 0%.
Edit: hit enter in wrong place, adding pics etc...
Best Answer by Spegelius:
Well I finally did what I should have done in the beginning had a good look at filaswitch output gcode. Turns out there was a bug in filaswitch code. Hard to believe, I know :). Ain't the first, ain't the last...
The bug was in a bit of code that I added few years ago for making sure that there aren't any 'incomplete' retracts. I can't even remember why I added it, maybe some slicers were behaving badly at that time or something. Anyways, the "Retract amount before wipe"-setting caused the retract to be split in multiple commands, some during wipe movement and some regular extruder move. Filaswitch calculated the retract amount correctly, but in the last check compared it in wrong way -> the residual retract was done twice -> gaps in print. That's why changing RABW to high number fixed this, most of the retract happened before the check.
I can't remember why I fixated on blaming other things than filaswitch when I first noticed this issue. Probably just assumed that it's just a random bug and since RABW-setting fixes it, moved on. Clad that I revisited this and found the actual issue.
RE: Extruder "Retract amount before wipe"-option and underextrusion
Ah ok so I can't edit the original message again. Nice.
Well here's the info I spent 15 minutes writing only to be greeted with some timeout...
Picture of single color print, no issues, RABW 0%
Pictures of dual color print, underextrusion. RABW 0%
And finally same dual color print, but with RABW 80%
So quite severe issues in some places. So far changing the RABW setting has made any difference. I tried disabling linear advance because I thought that it might be freaking out for some reason, but didn't do anything. And since this issue has been here before Arachne was a thing, I really have no idea what to change... Also the strange thing is that single-color print works fine, but with multicolor this starts happening.
Anyone else seen this?
RE: Extruder "Retract amount before wipe"-option and underextrusion
Oh and when I first stumbled on this behaviour, I also tried setting this option 100%. No underextrusion, but it seems there's no wipe at all. I guess "Wipe while retracting" and 100% retract before wipe means there's no wipe to do...
RE: Extruder "Retract amount before wipe"-option and underextrusion
Well I finally did what I should have done in the beginning had a good look at filaswitch output gcode. Turns out there was a bug in filaswitch code. Hard to believe, I know :). Ain't the first, ain't the last...
The bug was in a bit of code that I added few years ago for making sure that there aren't any 'incomplete' retracts. I can't even remember why I added it, maybe some slicers were behaving badly at that time or something. Anyways, the "Retract amount before wipe"-setting caused the retract to be split in multiple commands, some during wipe movement and some regular extruder move. Filaswitch calculated the retract amount correctly, but in the last check compared it in wrong way -> the residual retract was done twice -> gaps in print. That's why changing RABW to high number fixed this, most of the retract happened before the check.
I can't remember why I fixated on blaming other things than filaswitch when I first noticed this issue. Probably just assumed that it's just a random bug and since RABW-setting fixes it, moved on. Clad that I revisited this and found the actual issue.