PETG Infill Rot

[petej]

Over the past week I was having lots of problems printing PETG -- nasty tangles on the third or fourth layer of a large print, and the nozzle was getting furry with clumps of filament, causing more messes. On day five I finally took a long look at the printer and realized that when I leveled the bed I'd rotated the outer fan away from the extruder. As a result, the PETG wasn't cooling quickly after it extruded, so it turned into squishy snakes looking for trouble.

I changed the fan position and started another print. Issue gone.

Perhaps you need to adjust your fan position or its speed.

[jimc]

pyro, i have seen petg infill do that many times. that is or actually was a big problem when petg first started coming into the 3d printing scene and before we figured out how to print with it. you have a couple problems here causing that. #1 your printing too hot. drop your temp from 255 to 240-245. i assume you are using s3d? if so dont use rectilinear infill. it only prints every other layer. if you want to use rectilinear then you need to bump up your infill extrusion width to 140%. basically rectilinear prints every other layer so your bridging on all those little infill squares and since petg doesnt bridge well it breaks apart and starts this downward spiral where it just gets worse and worse. the lower temps help it bridge better so its less gooey. the 140% infill width extrudes more material so it will bridge better as well. i usually use fast or reg honeycomb. it wont have this problem. i only use rectilinear on very high infill, 80% or better.

[pyronaught]

What thickness of MIC6 are you using? It looks like you don't see the high tolerances on levelness until you get to 3/4" or thicker. At 1/4" I'm seeing .015" tolerance, which is no better than glass. Not that I think it matters much, glass is plenty flat. You can have a super flat plate and all that accuracy goes out the window as soon as you put a sheet of adhesive over it. The high thermal conductivity of aluminum is nice to have though. It looks to me like the heat bad under the build plate spans the entire plate though, so I don't see how the corners would be cooler unless you are way out on the very edge.

[pyronaught]

Over the past week I was having lots of problems printing PETG -- nasty tangles on the third or fourth layer of a large print, and the nozzle was getting furry with clumps of filament, causing more messes. On day five I finally took a long look at the printer and realized that when I leveled the bed I'd rotated the outer fan away from the extruder. As a result, the PETG wasn't cooling quickly after it extruded, so it turned into squishy snakes looking for trouble.

I changed the fan position and started another print. Issue gone.

Perhaps you need to adjust your fan position or its speed.

Well, I've completely removed the lower fan on all my printers. I thought only PLA required them. Maybe that's the issue?

[jimc]

No fan needed with petg. Only on maybe very tiny parts where heat soak would be an issue. A fan may cure your issue but only because your nozzle temp will drop about 10 deg with it on. Just forget the fan, lower your temp and change your infill pattern. Your mic6 sould be flatter than that. It really depends on how your sheet was stored. If the shop you bought from had the sheet leaning against the wall for the past year then your going to lose the flatness. It should be within .001-.002" across the surface

[Slipshine]

What thickness of MIC6 are you using? It looks like you don't see the high tolerances on levelness until you get to 3/4" or thicker. At 1/4" I'm seeing .015" tolerance, which is no better than glass. .

I have a tendency to agree with this. My mic 6 plate is .012 inches out on one side fortunately the other side was within .005. My first glass plate was within .003 .
The backup glass plate I have is about .006 . I went to the Mic 6 thinking I would go to a prox sensor for the z axis and after 3 years the glass started pulling chunks out of the surface.

For the extra pound of weight the Mic 6 adds if I had it to do over I would probably just put the .03 PEI over the glass.

[pyronaught]

pyro, i have seen petg infill do that many times. that is or actually was a big problem when petg first started coming into the 3d printing scene and before we figured out how to print with it. you have a couple problems here causing that. #1 your printing too hot. drop your temp from 255 to 240-245. i assume you are using s3d? if so dont use rectilinear infill. it only prints every other layer. if you want to use rectilinear then you need to bump up your infill extrusion width to 140%. basically rectilinear prints every other layer so your bridging on all those little infill squares and since petg doesnt bridge well it breaks apart and starts this downward spiral where it just gets worse and worse. the lower temps help it bridge better so its less gooey. the 140% infill width extrudes more material so it will bridge better as well. i usually use fast or reg honeycomb. it wont have this problem. i only use rectilinear on very high infill, 80% or better.

That is strange about rectilinear skipping layers, I've never noticed that before. I've always used rectilinear for everything. The only other option I see is concentric though. I'm getting the problem on 80% infill too. What speed are you printing PETG?

I'm still nervous about nozzle jams with PETG, which is the second biggest problem that has been killing my PETG prints. At least with ABS it is easy to recover a partial print left by a nozzle jam by starting a new job that prints the remainder and gluing them together. I don't think you could reliably do that with PETG.

Just ordered some ABS+ to try.

[jimc]

Sure you can glue together perg parts together. I dont print with support so my parts are always glued. For the infill, concentric is only top and bottom surfaces. Look at the drop down for infill patterns. Choose one of the honeycomb patterns. You should only get jams with petg if you tension screw is too tight. In 40-50 kg i have had maybe 1 jam. My print speed is 3600mm/min with a .5 nozzle. I can print at that speed up to maybe a .75 ext width

[pyronaught]

Sure you can glue together perg parts together. I dont print with support so my parts are always glued. For the infill, concentric is only top and bottom surfaces. Look at the drop down for infill patterns. Choose one of the honeycomb patterns. You should only get jams with petg if you tension screw is too tight. In 40-50 kg i have had maybe 1 jam. My print speed is 3600mm/min with a .5 nozzle. I can print at that speed up to maybe a .75 ext width

I was running an old version of S3D that didn't have the new infill patterns. I installed v3.0 many months ago but it doesn't overwrite the old version and doesn't update any of the start menu or desktop icons so didn't even realize I was running the old version. So I'm running 3.0 now and tried the honeycomb infill but the g-code parse time when preparing to print was outrageously slow and then ran my computer out of memory. The grid pattern was very fast though, will that one work?

3600 mm/min is just too slow and would take three days to finish the part. Even at 6000 it takes almost two days to finish, so that's as slow as I want to go. I'm guessing the non-rectilinear infill patterns are going add a bunch of time to the print as well.

[jimc]

Ok you need to download the latest s3d release. Its 3.1. 3.0 had lits if bugs. S3d never over writes the old version so you can always go back. As for your speed, your probably better off with an e3d volcano. It will exctrude way faster. You can only push filament through a hot end so fast before the back pressure takes over and you strip it out. All depends on your layer height though and extrusion width setting. 6000 would be no sweat at .15 mm for instance but not at 0.3. Its just too much material. Fast honeycomb is as fast or a touch faster than rectilinear.