Large infill top layer almost immediately gets ruined trying to bridge

Question

Info about the prints:

• Using PrusaSlicer with 0.1 mm layer height
• Using PETG, 1.75 mm
• 240 °C nozzle, 90 °C bed
• 0.4 mm hardened steel nozzle
• Printing at 40 mm/s
• 9 top layers, 7 bottom layers
• Using 15 % infill (slightly more than recommended, trying to keep this low for weight)

Here's a timelapse of the full print (I don't have footage of each individual layer being added, but this somewhat shows what's happening)

I've done some research, and I think the general term for this anomaly is called "pillowing", but I think what I've encountered seems to be a much more significant and harmful version. Essentially, it seems to nail the infill parts relatively well, not messing up any of the thin walls, but right as it tries to bridge over them, it seems to fail, creating these odd chunks of chaotic shards. This eventually gets refined as more top layers are added, but I don't want to simply add more top layers, as it seems that 0.9 mm should be enough for most applications. This would probably be a lot more inefficient w/ more top layers, so I'm just trying to figure out the root of the issue.

I've also seen some resources saying that the temperature used is too high and that the temperature is too low, but those seem to have different-looking problems. I'm not sure as well whether the hardened steel nozzle demands a higher temperature as this is one of my first couple prints w/ it. Other than this pillowing problem, the walls seem to be smooth and well-defined, so I'm not sure whether I should change temps.

Answer 1

From what you've seen, it's not a high enough value for the infill, as it results in the pillowing you are experiencing. As you are describing that bridging the infill is problematic, the two are directly related.

You may be able to mitigate the problem by increasing the infill value or by changing the infill to a different pattern.

If weight is that critical, something has to give way. I would expect very little increase in weight by changing from 15 percent to 30 percent. Your slicer will provide estimates, allowing you to compare the existing print weight in the slicer and existing print weight for increased infill (or different pattern) and determine more accurately the change.

Also consider to print a temperature tower for your printer with the steel nozzle. This will ensure that your bridging is being performed at the best temperatures.