Issue with different material supports

[JustVic]

How do you print supports with a different material? I’m trying to print PETG while using PLA for the support interface

And here’s what I’m getting: after the material switch (PLA → PETG), the PETG layer simply doesn’t bond to the previous layer

I’m printing on a Bambu Lab P2S.

I print PLA at 220°C with the fan turned off, and PETG at 245°C with 40% cooling. Turning the fan off for PLA didn’t help at all, and the AUX fan keeps acting up (for some reason it’s almost impossible to fully disable it), Speed - 100 mm/s

I came up with the idea to add a modifier for the layers where the filament change happens and the support interface is printed. I set the temperature for those layers to 260 degrees - no results

Below I’ll show examples of my filament print profiles

Regular PETG profile

PETG profile for modifier

[Bullocks]

Set your purge to the maximum allowed. Material changes need to be very thoroughly purged.

[JustVic]

Changed 219 to 900, going to test it now, I’ll be back in a few minutes))

[Bullocks]

I’d change it to 900 in both directions, but lets see how it goes. (the cell listed 630)

[JustVic]

Unfortunately it didn’t work. The model is just as fragile and broke with almost no force

[JustVic]

Hmm, maybe the mistake was that I only changed the purge for 1 filament, while the modifier uses 5 at that time. Going to print again

[Bullocks]

Are the 3 layers where both are being printed still stringing off and unadhered to one another? Hard to see.

This specific test object is gonna be fragile to pressures acting in that little wedge, and will need to pry the support interface off lengthwise. But youll need to be the judge of what is too fragile and what isnt. Imagine this was wood, and you just cut that wedge with the grain the same way this hole is “with the grain” via z. It’s a perfect lever against that rigid body.

[JustVic]

Well, WE DID IT! It really was my mistake – I changed the purge for the wrong filament the first time. Thanks so much for the tip! I spent half a day experimenting on this. Now I’ll roll back my experiments with modifiers and turning off fans in the profiles

[RocketSled]

You need massive amounts of purge going back to PETG. The slightest amount of PLA will contaminate the next layer and the print will be significantly weaker. Since PETG is generally used for functional parts, you usually can’t afford the weakening. It will look just fine with insufficient purge, until you stress it.

I gave up using PLA for PETG supports. I went back to designing my prints so I didn’t need it. Everything I printed with PLA support broke when I used it.

Split it model and flip the top over so there are no overhangs, bond the two halves together afterwards with MEK.