PETG Infill Rot

[pyronaught]

This is a frustrating problem I've started having recently when printing with PETG. I call it "infill rot," because once it starts it grows on each successive layer and has the appearance of termites eating the inside fill area. Once started, the print usually can not recover from this because it creates a rough surface that sticks up into the next layer and makes each successive layer worse than the last. The nozzle starts accumulating an excessive amount of blobs once this starts too. It's just a chain reaction that does not end well, and it can spring up out of nowhere on a print that has been going fine for several hours. I've even tried to recover a print in process by sanding down the rough surface in hopes that the next layer will be able to pave over the mess, but this has never worked. Once it starts, you might as well just cancel the print job because it will eventually self destruct.

The example here is e-sun PETG being printed at 255 temp, 4000 speed and 80% infill. I suspect the problem only happens on partial infills, as all my previous PETG work has been 100% infill and I've never seen this problem. At 80% I see it every single time though. I've tried different extruder temps and print speeds but just can't seem to eradicate it.

[Jules]

Good grief pyro, what the heck are you doing? I've never seen PETG do that....ever!

(Awesomely weird, actually!)

I know you were printing a lot of filter plates for your hydrogen generator and were pushing the speed to get them done in a timely basis, but it might be time to take the speed down to 3200 mm/min. Take the temp down to 245°. Maybe it's too hot for the PETG (burning it and turning it into cottage cheese). Lower and slower.

Maybe you've got some bad filament.

[pyronaught]

This isn't for the hydrogen plates, those were all ABS and 100% infill, 265 temp and something crazy like 8000 speed. But those all printed fine. This thing here is a thick walled shell that will be filled with plaster and used for pressing molds in a press. The wall thickness is about 1/2" and it damn near fills the entire build plate. I've taken the speed as low as 4000 and the temp as low as 250 but still get the problem. It looks like the infill traces break and the ends of the break flip up and cause spikes that then cause successive infill lines on the layers above it to also break and do the same thing. So it is a chain reaction that starts small and grows larger with each new layer. It might be caused by blobs on the tip sticking to the trace and breaking them. ABS never does this, which is why I've switched back to it and decided to do battle with the massive warp forces this part has to withstand at the corners. Even the PETG started to pull loose at the corners, but not as bad as ABS. It just seems that ABS is much better at healing over any defect that occurs on a layer compared to PETG. I can also print this giant part at 6000 speed with ABS, which makes a difference of about 10 hours compared to 4000. Going even less than 4000 would turn it into a solid two day print job.

But yeah, I've had more printing problems in the last week than I've had in the entire last year!

[Jules]

Yeah, you need to slow it down for PETG, and make sure you have enough adhesive on the plate. 3200 mm/min. 245° temp.
PETG sticks to itself very badly, causing all of those blobs to get dropped off into the infill if there is anything sticking up in it's way.....you need to spend extra time making sure the gap is perfect and the tension is correct, but once you get it dialed in, it's practically worry-free.

But it is slow.....you might want to keep working with the ABS, since it can be printed a lot faster.

[pyronaught]

Any slower and I just can't take how long the print time will be. I'll just stick with ABS, which also sands better than PETG and this part will require some sanding. PETG is very resistant to abrasion, which I suppose is great if you are making skid plates for skateboards but it sucks for sanding out defects. I also like that ABS cement works so well for gluing ABS parts together, whereas PETG is difficult to glue. Even with the correct Weldon cement for gluing PETG, it is a very thin glue that doesn't handle gaps or voids well and has a long clamp time requirement. With the failure rate I'm having on this 30 hour print, I've been recovering the incomplete prints by starting a new print where the old one left off and then gluing the pieces together rather than starting over from scratch. I've even considered just intentionally printing the model as five slices just to throw five printers on it in parallel. The female half of this mold is even larger than the 30 hour male half!

I was just curious if anyone had ever seen this infill rot problem, because it is a real show stopper.

[Jules]

Yep! That it is!

You know, for your warping problems at the corners......if you are going to keep printing things that span the entire plate, you really need to look into a MIC6 plate with a PEI surface on it.

Insta does the MIC6 plates - he might still have one available for purchase, and you can apply your own PEI surface to it. (Amazon sells them and the tape you use to apply it.)

The benefit to the MIC6 plates are a perfectly flat print surface that heats up all the way to the very edges of the plate. (No warping at the corners any more as the print cools there.) The benefits of the PEI sheet are....prints stick to it. No adhesive needed. They let go when it cools off. No muss, no fuss.

You print enough full plate stuff that it would be a good fit for you. (Note: You will have to reset your Z - they are pretty thick.)

[insta]

pyro you need me to print parts for you yet?

[pyronaught]

I have a PEI sheet on glass I've experimented with, but I don't get as good of adhesion with that as I do the 5 mil kapton with abs slurry. Also the adhesive backing used to attach the PEI is a lot thicker than that used on the kapton sheet and winds up adding high and low spots on the plate.

What I like about ABS slurry is you can control how sticky it is by the % of abs or the thickness of the layer you apply. There's the "nuclear option" where you squirt the abs juice on a hot plate where you know the perimeter will be and then you don't wipe it off. You just let it evaporate into a thick abs layer that acts like a brim and really grips the plate (see image below). You don't want to use that unless you absolutely have to though because the part is really hard to get off even even putting the plate in the freezer, then you have to wash the plate in acetone to get the mess off of it. But that nuclear option will beat PEI and rafts for holding the part down. The only thing stronger would be putting a raft on top of it.

However, this part I'm currently trying to print is so warp prone that it is even ripping itself off the nuclear option (see below)! Normally once a corner goes the separation will spread around to the rest of the part and the whole thing will eventually come loose, but the sides of the box shown below still hold it to the plate for the remainder of the print. The corners don't peel till about two or three hours into the print once the wall height has reached about 1/2" tall, which is weird because that frame is really strong at that point and really hard to bend by hand. I really don't fully understand the mechanism behind how so much bending force gets generated by ABS. I wonder if it is really that the corners of the plate are cooler or if it is just that corners on the part are the most prone to start pealing. If I put a circle of the same diameter it will never peel, and rounded corners also seem less likely to peel. My theory is when you have a sharp corner that goes to a point, you have a spot that cools a lot faster than other areas because there is less thermal mass at that point. Then once the tip of that corner comes off the plate, it allows it to cool that much more and the reaction feeds on itself.

[Jules]

I think you can use the ABS slurry directly on the MIC6,( right insta)? It's just flatter than glass, and it carries the heat all the way out to the edges. (Which you need for something that large.)

Talk to insta. He prints ABS on his MIC6.

[insta]

I think you can use the ABS slurry directly on the MIC6,( right insta)? It's just flatter than glass, and it carries the heat all the way out to the edges. (Which you need for something that large.)

Talk to insta. He prints ABS on his MIC6.

I print eSUN's ABS+ on MIC6+Kapton+nojuice.

ABS+ is the secret sauce though.