PETG infill failure  

RE: PETG infill failure

PETG has to be printed slower than PLA. Much slower.  This slowness allows time needed for the layers to bond properly.  Try starting with the supplied Plicer PETG profiles.

PETG also doesn't like having fan on. Again, a fan robs heat needed to make the weld work.

All print moves are determined by jerk, acceleration, and peak speed settings. A short run never reaches peak speed. Longer runs have a chance. So yes, you will see speed variations based on part size.

I can't even print PLA infill at 200 mm/s ... so remove that concept from your mind.

Setting volumetric limits (two places) to 4 mm3/s is an easier way to deal  with limitations. But even then you can still exceed "time on target" needed to complete the weld, and why setting the actual print speeds is almost mandatory for larger parts.

RE: PETG infill failure

Posted by: scott.b47

[...] My first guess is that I'm simply printing too fast. The profile I'm using has an infill speed limit of 200mm/s and a max volumetric flow of 8mm3/s.

That's very likely the issue, especially with a sticky material like PETG. PETG really wants to stick to whatever's hottest. If it doesn't lay down cleanly on the lower layer with good inter-layer adhesion, it'll curl up and find the hottest thing, usually your heater block or nozzle. Go too fast, and it doesn't adhere well with that previous layer. With PETG:

• Use minimal cooling (only as much as you have to, rarely more than 50%). This promotes inter-layer adhesion.
• Slow down. The default Prusa uses 8mm^3/s MVS, which sounds like what you're using. Also cap maximum speeds (incl. infill specifically).
• Consider a silicone sock for your heater block to help keep filament from accumulating there and eventually snagging lifting infill.
• Consider a coated nozzle. for the same reason I've had good luck with E3D nickel-coated copper and P3-D's coated Apollo series.

Previewing the model showed multiple areas of infill reaching 125mm/s with these settings. Interesting the whole infill wasn't like this. Some of it was at 30, some at 70, and some at 125. 125 appears to be about where the volumetric rate capped it. So here are my questions:

1) Why does the infill speed vary layer-by-layer? My naive assumption would have been that infill would have generally been set to the same speed. 

You're seeing to effect of Max volumetric speed (MVS) kicking in I suspect. It may vary depending on what features are being printed, as they may have different extrusion widths. The slicer will use speeds up to your individual speed settings up to the point that the Speed X Layer Height X Extrusion Width exceeds MVS, at which time the slicer will reduce speeds. That doesn't mean it won't hit higher speeds than your filament will print well at, and 200mm/s is way too aggressive for most filaments. AtomicFilaments doesn't list a maximum recommend print speed, but for PETG, I suggest:

• Dont' try gyroid infill. It's too delicate. I go with good old Grid for PETG most of the time. Nice, simple and straight lines.
• Keep speeds to 70-80mm/s until you gain confidence with the specific filament.
• Knock back MVS a bit (0.5mm^3/s) if you experience extruder clicking or jams.

Keep in mind, there is a minimum layer time setting that will also throttle speeds back. If your layers are small, this can kick in if set too high.

2) Is it better to limit my infill speed in `print settings` or to limit my volumetric rate in `filament settings`. I could set 60mm/s in the former, or set 4mm3/s in the latter and achieve approximately the same effect. Perimeters aren't affected by reducing the volumetric rate because they're already printing at a lower rate.

Both, honestly.

• The MVS setting will keep you out of trouble overall. I set 11.5mm^3/s as my limit in my Print Settings tab (corresponding to the E3D V6 MVS rate with a bit of safety margin), and adjust it for each specific filament in the Filament Settings tab. This way, if any of my settings result in excessive speeds, it'll throttle back, sort of a governor (like on the old go-kart tracks).
• Meanwhile, your specific speed settings for each feature let you maintain quality and maximum speeds. I'd cap infill and do a bit of experimentation. Keep external perimeter and infill speeds nice and low for smooth finish quality.

3) Anything else I should look into?

Just a couple:

• When you start to hear it rub against the infill, dial back speeds using the front panel and you may be able to complete a print that's at risk of failure.
• On the 1st layer, you might bump back the nozzle temp and increase the bed temp to encourage the filament to go for the print surface instead of the nozzle.
• A few other notes here.

I see a slight bit of variation between PLAs, but the copolymers like NGEN and PETG really seem to need a specific profile for each brand of filament. Each one seems to have a bit of "personality". For ease-of-use, stick with a brand you like. Otherwise, spend an hour or so doing a bit of calibration for each new brand.

RE: PETG infill failure

There is no universal formula the PETG filament itself, every manufacturer can and does use a custom blend of raw materials.  the blends can vary a lot in melting temp, best extrusion speed, glass transition temp. also the added materials like pigment sparkles and fibers will affect those parameters. it's a good idea to create a a custom filament profile for at least every brand you print with and even the specific filament model and color. 

RE: PETG infill failure

Thanks for the responses, they are helpful. I did reprint the part this morning with the 4mm^3/s volumetric limit and it did print fine. I think 4mm^3/s is perhaps a bit slower than it needs to be, as it was a case of me erring well on the side of caution. Maybe trying the print somewhere in the middle, around 6mm^3/s would be s useful data point. The silly thing is that the lower limit doesn't even add a significant amount of time to the print. It's 4 minutes difference on a 4 hour print. If the difference between complete success and epic failure is a less than 2% increase in print time, then it seems like the 4 minute increase is a small price to pay. 

I should have mentioned in the OP that I am running a sock, and I am running a plated nozzle (E3D Nozzle X), though I haven't taken a close look at the quality of the plating lately. Probably worth a look to see how it has been holding up. I do use grid infill for my PETG prints. I do have the fan limited to the automatic 30%-50% that was inherited from the Prusa PETG profile.

I suppose part of my confusion in the OP is that it seems like there are filament-determined properties (maximum infill speed) that end up going in the print settings tab. I would have expected all filament-determined properties to go into the filament tab, so it's easy to confine the settings in one place, and easy to change filaments. I was trying to fold everything I needed into the volumetric limit, since that is in the filament tab. I'll just have to wrap my head around needing to create both customized print settings and customized filament settings to accommodate some of these materials.

Scott

RE: PETG infill failure

Posted by: scott.b47

[...] I suppose part of my confusion in the OP is that it seems like there are filament-determined properties (maximum infill speed) that end up going in the print settings tab.

The only one I'm aware of is the Max volumetric speed setting under Filament Settings->Advanced. I do wish there were more filament overrides though. 

[...]  I would have expected all filament-determined properties to go into the filament tab, so it's easy to confine the settings in one place, and easy to change filaments.

IdeaMaker is another free slicer with some really good ideas. One is that you can override any other setting in your filament profile. This is really handy for when you're using an experimental filament with odd requirements. My perfect slicer would allow any tab to include overrides on any of the others. Sometimes you want to adjust your extrusion widths depending on the nozzle mounted for example.

I was trying to fold everything I needed into the volumetric limit, since that is in the filament tab. I'll just have to wrap my head around needing to create both customized print settings and customized filament settings to accommodate some of these materials.

I've found a middle ground. I keep a "quality" and "speed" set of profiles for each layer height. I generate a lot more layer height profiles than I need, but I like to tinker. Those to categories set the speeds, with the quality set being very conservative. Then I set MVS under filament to whatever's appropriate. This has kept me from too many iterations of settings.

RE: PETG infill failure

the nozzle-x is a coated steel nozzle - you will need to raise the printing temps. (probably around 20 deg from whatever the default is for the selected filament). i expect if you examine your latest prints you will find the plastic is dull not shiny and the layer adhesion is not very good.

RE: PETG infill failure

Im using a nozzle-x and i havent had to change my print temps at all.  I mainly print pla at 210 and thats working fine with the X.