Ok. I misunderstood and was wrong. I apologize.
I am sufficiently embarrassed. Sorry for being harsh.
Again, apologies.
1 Like
Hi Jay,
Glad to see you are back. And passionate as always 
Regarding heat creep in a dissimilar material print with PETG as model material, I did actually have similar experiences as @RocketSled . His illustration below, tracking the root cause to the cold end fully matches my observations.
When I had those issues, it was fortunately enough to just set the Min/Max temps of both materials into the printable range for both (i.e. Min/Max identical for both PLA and PETG: PETG Minimum and PLA Maximum).
Since then, Bambu has however added a line to the Filament change code to always heat to 250° with PETG (which can be too much for PLA from my experience).
I think it is this one but have not had the case again to test.
I am however not convinced that this alone will always help. From my experience, the temperature range for the cold end is actually rather tight. And I have not had the opportunity or means to measure this critical part.
However, from Impact of the Fused Deposition (FDM) Printing Process on Polylactic Acid (PLA) Chemistry and Structure, there is a lot happening with PLA in terms of material behavior at pretty low temperatures that I expect are realistic to occur in the cold end when printing PETG. In particular the drastic change in heat transmission around the “cold” crystallization temp.
So it is rather important to keep the cold end below the crystallization temp.
Best wishes,
Eno
PS: It took me so long to go through various graphs and books that your response beat me to it 
I’ll post this anyway as it may add to discussions and understanding… Or at least to more question 
2 Likes
I’m glad we figured it out. 
1 Like
You know for about $50.00 you could put a temperature sensor or 2 or 3 all along the filament path and tell pretty conclusively what is going on in and around the toolhead.
I have a FLIR.
But I gave up on PTEG with PLA supports. Even if I solved the PLA jamming problem, an absurdly high purge volume is needed to ensure all the PLA is purged or the PETG easily breaks along layer lines. Faster to print without supports, and at higher quality, with parts broken up to minimize/eliminate overhangs and glued together after…
The AMS switchable filament is great for color printing. Less so for supports. For dedicated support material, to avoid cross contamination, IMO the printer really needs to have two dedicated printheads. Feed the AMS to one of them, you still get multi color printing, and feed the dedicated support material to the other.
1 Like
Just a thought, have you considering ABS+ as support for PETG?
I tried ABS+ before by mistake, constant clog with ABS profile but then I realized it was ABS+ and use PLA profile. Since then it printed flawlessly.
Have you tried using the same petg for the supports?
May be an apples/oranges comparison but I use the same PLA I’m using for the print for the supports. Works like a dream.
It’s the temperature delta between the primary and support filaments that’s the issue. So another type of plastic with a similar temperature profile to PLA doesn’t help. It’s not that PLA doesn’t work, it’s that PLA melts at too low a temperature.
Mostly, I just use the same filament for supports where I need supports. Doesn’t matter what the filament is, if flow and temperature are properly tuned, supports pretty much fall off and don’t mar the surface they leave behind.
But the quality of an overhang supported this way is inferior compared to a surface with dedicated support material. With dedicated support material you get an overhang that basically looks like it was printed on the build plate…
But most of my stuff is mechanical, not decorative. Can’t afford weakness from incompletely purged support filament. If it wasn’t for the purge requirement, though, I would always print with dedicated support material because the results are superior.
1 Like
@stewart
I got my problem solved by install an extruder cooler. It cools down the extruder effectively without needing any hardware changes. haven’t had any clogging problems while printing PLA since I installed it. I don’t want to leave the door open while printing cuz I have cats in house and an open chamber causes warping and other issues too. So… the extruder cooler is my best solution by far. I picked it up from x2hammer. Hopefully this can help you guys too.
1 Like
Been looking for something like this! I was just going to pipe in air from a laser air assist unit through a wye but this actuall refridgerates the air. Very nice. Wish it wasn’t so pricey though…
One thing that has not been discussed here is an additional source of heat in the extruder and that is the motor. I had many failures this week on a 22hr print and while clearing the last issue I touched the motor to see how hot it was and could not keep my finger on it for more than half a second it was so hot. Granted, there’s alot of poorly conductive plastic between it and the the drive gears but for that long a period of time with that much heat enclosed next door, I think that is a big contributor to this whole issue. That is, unless I have a motor that is running unusually hot. Mind you this discovery happened DURING a print while the motor was still under current, not after while it was not under current. I think this overheating even caused extruder to lose steps at one point and severly underextrude some sections. Thoughts?
