Polycarbonate Mess

[LEGOManiac]

This is 3DPC’s PC+ filament 240C/120C.

On the first attempt, it shattered the glass (2nd time in a week), although I think this time it was caused by the high bed temperature specified on the filament roll, combined with the fact that I’m in a cold basement and the glass overhangs the bed by several cm which could cause a substantial temperature variation between the middle and the edges.

After switching to a magnetic build surface, which has to be clamped down because the glue wants to separate those temperatures, I printed a model overnight. It had some obvious defects on the surface but the oddest one was that it seemed “squishy” like the 20% density cubic infill was missing.

I printed another and watched it:

Strangely, the tree supports came through undamaged. The damage seems limited to the infill.
Then came the time to put infill over the area that was supported by the tree supports. This also got gouged out.

I’m at a total loss as to what’s going on here. I had changed the infill to 50% density and triangles, hoping this would make it more solid.

As you can see, it’s almost as though the nozzle was digging out the infill as it went along and depositing it as a steady shower of plastic bits all over the build plate. The fact that entire sections of infill where hollowed out in this way explains why the previous attempt felt spongy. On the second attempt it didn’t even manage to complete the outer shell.

Does anyone have any idea why it’s behaving like this?

[Jason]

that is bizarre, I have never seen something fail like that before.

If you print the same print with PLA would it be successful? I’m curious if the PC is warping differently than the PLA and causing the issue?

Just an initial thought.

[Glenn]

Does it seem like the filament stopped sticking to itself while it was extruding?

Maybe the print shrunk away from orwarped away from the nozzle?

[kitedemon]

I have see PC lift in places and not others. I wonder if it lifted and caused the nozzle to catch in the higher parts and miss the adhered spots?

[LEGOManiac]

Thank you for your respective inputs.

The model did not warp. Indeed, I had a heck of a time getting it off the build plate.

I wouldn’t describe it as shrinking or warping away from the nozzle, in fact quite the opposite. It’s the infill repeatedly colliding with the nozzle that was breaking small bits of it off, ending up with the infill being hollowed out.

The bizarre thing is, it didn’t happen with the tree supports, which were undamaged (Photos 1 & 2).

The fact that the pieces of infill broke off so easily means they were obviously not firmly attached to the layer below (although that should have applied to the tree supports as well). I’d have to check the settings; perhaps the infill prints faster than the tree supports.

While the tree supports came off cleanly, the dome they were supporting is also a mess. It’s my somewhat amateur opinion that it indicates the filament was too cold as there are clearly areas where it came out as a string rather than sticking to the layer below.

I’m mulling a theory around in my head that, because the build plate had to be very hot, the initial layers came out fine since contact with the hot build plate kept the filament from cooling too quickly.

When it gets up into the infill, it’s away from the heat of the build plate and more acutely influenced by the much cooler basement air temperature. I’m thinking this would cause the filament to solidify before it had properly bonded with the layer below making it easy to flake off on impact.

Mind you, that doesn’t explain why the tree supports were not damaged.

Does anyone care to comment on the theory?

I don’t have an enclosure, but it makes me wonder: for those who have printed ABS, does it behave similarly if printed without an enclosure? PC is the only non-PLA filament I have ever used.

[Glenn]

@LEGOManiac

When it gets up into the infill, it’s away from the heat of the build plate and more acutely influenced by the much cooler basement air temperature. I’m thinking this would cause the filament to solidify before it had properly bonded with the layer below making it easy to flake off on impact.

On mine when the nozzle hits the infill it’s with a lot of force. I use gyroid now mostly because the pattern doesn’t have places where the path crosses itself on the same layer. Also I learned that you can increase the thickness of the infill “strands” and cut way back on the amount of infill you need and still have the same strength, also better speed. I can see if a material is brittle it could fracture when the nozzle hits the thin infill strands

[TurkeyOnRye]

@LEGOManiac

When it gets up into the infill, it’s away from the heat of the build plate and more acutely influenced by the much cooler basement air temperature.

I’ve actually had a similar failure to this! Not nearly as drastic though. I stopped the print when I noticed some of the infill was getting scrapped and chipped by my nozzle, but my trees were also fine. I found it super strange because I use z-hop specifically to try to avoid that!

I was printing in ABS when it happened, and adding a quick enclosure seemed to solve the problem. My guess was that it was cooling down at different rates in the denser areas of the print, leading to uneven cooling and some buckling of the infill/walls.

Not sure of your having the same issue or if an enclosure might help. Just wanted to chime in.

[ElrinV]

I think your intuition is correct with the cold temperatures. PC likes the air as hot as possible. I print PC at 50C enclosure temperature, and would print at higher air temperatures if I could. Also check your part fan settings - fan should be off completely (except a little blip for overhangs).

Try to close up your printer - even an unheated enclosure would make a huge difference.