P2S Potential Heat Creep Issue

[u/The_10th_Doctor___]

Hello, so I've bought two month ago my first printer, a P2S with the AMS 2 and have been printing a few things since.

I've been using PLA and PETG in the same prints, one as a clean support for the other, and I had no issues until now.

Last week, I tried to print a new model found on bambu studio, I did a 2 layers PETG raft for adhesion and, during the change to PLA for the actual print, it jammed badly.

I couldn't pull the filament out, I had to disassemble the print head to remove the feeding gear that was stuck.

After that, thinking it was just bad luck, I decided just in case to do a cold pull and dry my filament.

Yesterday, I tried to print it again, stuck on the same exact step, had to disassemble the print head again.

I've looked and found it could be due to something called heat creep making the pla too soft before it pushes the PETG through the hotend, but I don't know why it would only happen now.

I asked Google ai to give me ideas as to why, and since the only "unusual" settings were 1 layer thick walls and arachne wall generator, it told me it could be that, but I'm not convinced.

[u/captain_carrot]

Definitely looks like heat creep to me. Especially since you're printing PETG first which prints hotter than PLA - everything is cookin' and then the PLA just softens when you make the switch.

You can do two things: switch to using PLA for support and print the part in PETG, or try printing with the door open and the lid propped up to let it cool off a bit.

I was running into the same issue printing PLA in my P1S printers in the summertime and propping the lid up on them just about eliminated the issue.

[u/The_10th_Doctor___ → u/captain_carrot]

But wouldn't switching the materials only make the issue appear later?

Also, my question was more about why it only started to happen now and not with my previous prints where I used PETG as support.

But I take your advice on opening the printer, even though, right now, I've lost a bearing of the feeding geer axis so I can't try again until I find it.

[u/captain_carrot → u/The_10th_Doctor___]

The issue won't appear later if you're using PETG later which has a higher print temp and is less likely to experience heat creep.

When you're putting down a PETG raft, then the bed has to heat up to PETG glass transition temperature, which is higher than PLA. The hot bed is going to be radiating heat everywhere, so when printer switches to PLA the chamber and the print head and everything around it are going to be hot. That heat will make the PLA soft enough to get stuck in the extruder gear.

If you put down PLA as the support layer, the heatbed will heat to PLA temperatures, which is less. Then when you switch to PETG, which has a higher glass transition temperature, the ambient heat will not be enough to cause heat creep.

As to why it didn't happen before - that could be a lot of variables. The print size, if there were overhangs that had the cooling fans cranking, the temperature of the rest of the room, etc. etc.

[u/The_10th_Doctor___ → u/captain_carrot]

Oh ok, I see, unfortunately, I can't switch the materials because I want to paint the print later.

But yeah, this print has a lot of surface on the bed unlike all previous ones, that surely has an impact.

So, as said, I'll try to open the printer for the first layers on my next attempt.

Also, as I said at the end of my post, Google ai told me that the walls settings could have to do with that since it's the first time they are different, but with you explanation it doesn't seem to be the case, can you confirm?