TPU head sitting and oozing after tool change
So I've been experimenting with TPU (Overture HS TPU) on the XL for a few weeks now, and I have been noticing that in multi-tool prints it will switch to the TPU head, and then sit in the corner, sometimes for like 30+ seconds while it oozes out a ton of TPU, and then resume printing. It only does this on the TPU head. Other heads just start printing right away once swapped t0.
The oozing is all piling up in the corner since I keep the TPU on Tool 5, and it hasn't ruined a print yet, but is still concerning and it is causing lots of stringing on the edges of the TPU part of the print because it keeps oozing on its way over to the part.
I can't figure out why it just sits there for so long. Is it just getting up to temp? It seems like it's hot enough since it's oozing a ton. and if that's the case, why haven't I ever seen it do that with the other tools? It prints cooler than PETG.
I'll try to get a video of it happening on my next print if I can't fix it before then.
Thoughts on what settings to play with?
RE: TPU head sitting and oozing after tool change
Is this only on tool 5? Can you try changing the filament type to something non-flex under Filament Settings -> Advanced and try again? AFAIK this setting actually doesn't do anything, but acts as a filter whether to execute some filament specific gcode. Also check the custom gcode for your filament for any weirdness.
I can assure you I've never encountered this, using the profile for Fillamentum 98A (with some retraction and temp changes), on tools 3-5. It should wait for temp in the dock, definitely not over the print surface.
RE: TPU head sitting and oozing after tool change
Is this only on tool 5? Can you try changing the filament type to something non-flex under Filament Settings -> Advanced and try again? AFAIK this setting actually doesn't do anything, but acts as a filter whether to execute some filament specific gcode. Also check the custom gcode for your filament for any weirdness.
I can assure you I've never encountered this, using the profile for Fillamentum 98A (with some retraction and temp changes), on tools 3-5. It should wait for temp in the dock, definitely not over the print surface.
Apologies for the late response.
I tried switching the type in my profile to PLA instead of FLEX, and it still waited after the tool change, which surprised me greatly.
I got a video of it happening this time though. (here's a link, the forum doesn't want to upload the video for some reason) Next time, I'll try to look at the temperatures to see if it's waiting for that or not. That still wouldn't make sense to me though as the printing temp I have it set to is below PETG's printing temp, and it never waits when it switches to PETG or PLA, which is very weird since I triple checked that tool 5 is set to PLA, both in the slice and on the printer, yet it still waits after changing.I think my next test will be with the same G-Code file, but this time load actual PLA into tool 5.
Also, something I should clarify; I am not printing with a wipe/purge tower. I don't see why that would cause this, but should I try a print with the purge tower just to rule it out?
I also looked at the custom G-Code as you recommended and did not see anything out of the ordinary, but I've attached a screenshot of it just in case as I am not super knowledgeable about G-Code.
RE: TPU head sitting and oozing after tool change
I don't think it has anything to do with the wipe tower. Since changing the FLEX setting had no effect, there's no filament specific GCODE or possible hidden firmware voodoo left. I'm just guessing now, but apart from some defect in that toolhead's dwarf board, the only thing I can come up with is heat creap or a faulty fan.
Unfortunately M142 is not well documented (at least I couldn't find much in the wiki) and Prusa specific, I don't know what exactly it does and when it gets executed. But lets just assume for now that it waits for <36°+some tolerance to be reached in the heatbreak, by controlling the heatbreak fan speed. Lets also assume the fans spin down a bit, or completely, when parked. If the filament is very heat conductive and still in the hot melt zone it would then start to heat up the heatbreak while in the dock (FLEX don't get pulled out 20mm like other filaments on park moves, I tried changing this but only got clogs). This would explain why it only happens with TPU. You could change it to S45 or something, should still be safe enough (but treat this like any other advice by random internet person). If it works then that's the cause.
Could also be your heatbreak fan is obstructed or failing and it doesn't show with less heat conducting filament. The TPU 98A I'm using seems to be a better heat conductor than PLA and PETG (based on how long it stays hot to the touch after extruding).
RE: TPU head sitting and oozing after tool change
Also I just remembered someone here had a missing grub screw for the heatbreak sensor. Can you double-check if it's there and tightened? If not, your heatsink temp is not properly measured. There's a nice breakdown video of the print head on youtube by Chris' basement. You should be able to reach that screw without disassembling anything.
RE: TPU head sitting and oozing after tool change
I still think it has something to do with my TPU profile, because last night I just tried setting tool 5 to the stock Prusament PLA setting, and, printing the exact same object as before, and it never waited.
But, you mentioning the fan made me remember that I also have had a puppy error a few times when booting up the XL. I know that is a communication error with one of the heads, but I never really investigated my machine as it doesn't happen very frequently and when it does it's always when booting up and power cycling once seems to take care of it. Probably a semi-loose connection from when I assembled it.
Do you think that could be the issue though?
I guess to rule out that, or a faulty fan or something, I could try moving the TPU to a different nozzle.
Will probably try that tonight if I get time, and then look into the puppy error and grub screw.
RE: TPU head sitting and oozing after tool change
That sounds like a plan. I cannot really comment on comms errors, because there anything is possible 🤣
RE: TPU head sitting and oozing after tool change
Update: I have tried 3 more things.
I printing with PLA loaded into tool 5 instead of the TPU (but kept the profile the same), and also tried printing with the TPU on head 3 instead of head 5. Both tests resulted in the head that was set to my custom TPU profile in slicer, waiting after a tool change. This lead me to think my profile is the issue, so to test that theorey, I tried chaning all of the tools I was using to my TPU profile, (modifying only the temperatures so there were no clogs)
This resulted in every tool waiting after a change, which I think proves that it is the profile.
Now, I have no idea what setting in the profile would be causing it to wait, so I'm open to suggestions to try there, but at least I've narrowed it down.
RE: TPU head sitting and oozing after tool change
Well, then grab one of the stock 95A profiles as a template (e.g. BASF), then measure&adjust diameter -> print&adjust temp tower -> print&adjust stringing test, then slowly increase volumetric flow until it fails. Good luck 😉
No idea what the reason is for your problem, it seems like there's nothing left that can cause it.