Printing with PETG and supports using PLA

Bambu Lab X1 Series Bambu Lab X1C
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I printed a bracket using PETG and PLA for supports. The final reults was that the supports almost fell off and the resulting PETG looked great. But when I flexed the prints the legs cracked at the places highlighted in red. The rest of the PETG has good layer adhesion and it very strong. But the layer around where the PLA is used caused poor PETG layer adhesion/strength. Any hints on what slicer settings might improve things?

pla support2
pla support21438Ă—883 322 KB

Correction. Replaced the screen capture. I depicted an all PLA support. This resulted in an 8hr print! Here is the correct one, using PLA at the raft interface.

Notice that using Tree(auto) the upper tree doesn’t have a PLA layer. I don’t know why. Using normal support does apply a PLA interface at both levels.

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You most likely need to increase the flushing volume between PETG and PLA. I usually use 800 but have seen that others recommend 999.

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Also consider that it is breaking at the layer lines. Lay it on it’s back to strengthen the top rail to hook connection and the bottom of the hooks will likely break. Standing on end might work if side forces on the hooks are small.

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I don’t think it’s a layer problem. I can’t snap the vertical legs below the red line. Originally I used 2 wall loops and there was some infill and it was too weak. But that was my error. I increased to 4 wall loops to eliminate the infill. I did print the thing in PETG with PETG supports and it’s plenty strong enough. So I think that @EnoTheThracian might have the right idea that its filament contamination. I will try again with a higher flushing number and report back. Thanks for the tips!

The current flushing value between PLA green and PETG grey was 341

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It is the flushing volume. Support filaments mixed with the main filament causes this every time. I had this same problem.

Increase flush and/or the size of the prime tower

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Hi, I agree laying the back is better. But I am going to try printing it as before, I’m curious to see if increasing the flushing works. Maybe it’s something new learned .

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Ah, thanks. I am printing it now with flushing set to 850. I have not changed the Prime Tower. Top to bottom I see it’s default settings are 35, 45, 3 in general which setting(s) is the best to change?

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There is a bunch of math on this page. Prime tower | Bambu Lab Wiki

Basically you just need enough wiping to make sure there is no dissimilar filament left on the nozzle. The prime tower makes sure the tip of the nozzle gets wiped off nicely. Only a tiny bit of filament can contaminate the other filament.

I prob wouldn’t change the tower unless the flushing doesn’t take care of it.

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You are just doing dissimilar interface layers right?

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Yes, that’s right. I have just finished the print. Increasing the flush amount fixed it. The final result is fine. So something new learned. Thanks!

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Just keep in mind that Bambu occasionally changes Flushing defaults. Try to make it a habbit to check flushing volumes after each Studio update.
I know I am…
… trying that is :rofl:

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