Hi! Looking for some advice here from friendly local experts.
I’ve printed this with Elegoo Neptune 3 Pro, 0.4 nozzle, Elegoo PETG filament, no enclosure. Using PrusaSlicer.
This print is basically all walls - the hex grid is thin. It’s 2mm thick and each segment is 1.5mm wide. I set 3 layers for walls in slicer. It was printed vertically, just as seen on picture.
The solid part of the print (back wall) came out just fine, but the hex grid part came… dirty. On the picture, there are a few hex segments that just broke off during the print at the base of vertical segments. And the rest of them have small loops of filament that stick outside of the intended surface, to the sides.
My suspicion is the print temperature is too low. I’m printing at 230, which is the low end of 230-260 range of the filament. But in my previous tests I noticed stringing that starts around 240, so I did a few other prints that were just fine at 230, and I made it my default temp for this spool.
Or is it just too fine detail for my printer with PETG? Or something else that I am missing?
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Late to the party, but…
How well tuned is your printer? This whole print is a torture test with lots of retractions and thin walls. For things to go well you will have needed to dial in flow rate, print temperature, cooling, and retraction. As someone else said, if the nozzle catches on an unsupported lever arm (aka one of the vertical pieces before a horizontal bridge has been completed) it can/will break it off.
If your printer has never pulled off this type of print before I suggest running through some basic tuning tests before worrying about potentially wet filament unless you live in a very humid environment. I live in a temperate climate where it doesn’t generally get that humid. My printer and filament live in my basement, which has a dehumidifier in it. I’ve never dried a role of filament and I leave spools unfinished for 6+ months. That’s not to say that you never should dry your filament or that doing so won’t improve print quality. I’m just trying to say that I have not experienced a higher rate of print failure with older spools.
Thanks again for the valuable feedback! I printed it again with higher temperature, 240. It didn’t change much, overall. Same print errors remained, however I got a few less of broken hexagons, so overall the print feels more sturdy.
Looks like the majority opinion here is to blame that all on wet filament. I don’t have the right equipment to dry it, so I’d probably just avoid printing similar parts with this spool, and take more precautions when it will be time for a next one. My drybox spool holder build is almost ready.
Looks like a filament moisture issue to me. PETG can get real weird unless it’s really dry. Temp is also a little low, but drying the filament will also fix the stringing issues you were seeing at 240
Yes. This absolutely looks like a moisture issue. Drying the filament will almost definitely help.
Thanks! I think I unpacked this filament about a month ago, and it was on open air for about two weeks, in 40-50% humidity. then I put it into a dry box with a box of silica gel, and it stays there at about 20% humidity. Until I take it out for a print. Is silica gel good enough for drying? I don’t have the drying machine.
Silica gel has worked pretty well for me to keep a spool dry for a couple months, but I’ve never tried to dry a “wet” spool with it, so no idea. I’ve dried petg spools in the oven before, and it worked out. Can’t remember what temperature, but I’m sure that’s floating around on the internet somewhere.
Also the silica gel only keeps stuff dry if it’s dry itself. You can also heat that in the oven or a microwave to do that.
So yeah I’ve found petg (or at least the cheap stuff I’ve bought) to be kind of a pain. But if you’re almost neurotic about keeping it dry, you can get some super nice results. I only use it if I really want something to be clear
In the oven??? But wouldn’t it just melt? I have a gas oven, I don’t think it can go too low. But I will look it up. Maybe microwave is a way to go. Thanks for the tip.
A lot of people use food dehydrators. You can even get a spool holder that feeds the filament to your printer and dries it at the same time.
Microwave will not work. Unless you’re incredibly careful/lucky, you’ll ruin your filament. You can use your printer’s heated bed to dry it. Look up how to do it online, but basically you lay it on the bed, put a box over it to enclose it, turn the bed to 55°, and let it dry like that for 10 hours. That’s for PLA though, so you may have to go hotter for PETG.
Silica gel works to keep it from getting wet, but it won’t work to dry it, since the filament wants to hold on to that water. The only way to get the water out is to use heat. (Or maybe a vacuum chamber, but heat is a lot easier.)
Yeah, my oven is electric. Internet says 65C, which is conveniently as low as my oven goes
Yes, I second making sure the filament is well dried before printing. It usually fixes issues like this for me.
It looks to me that more is going on here than just how dry the filament is. I see a lot of deformity on the underside of overhang structures which makes me think that the temp is actually too high for the speed that your printing at. I would guess as the plastic went down it was curling edges upwards into the height of the next layer and eventually the nozzle hit this plastic that was too high causing some damage. What speed are you printing at ? Petg likes to print real slow in my experience. Like 20mm/s or less gives it more time to cool. I go as slow as 5-10mm/s when I’m using a large nozzle, but with a .04 you can go faster. Lowering the nozzle temp will reduce the puddling and curling up effect.
I don’t dry filaments because I don’t care that much about things being perfect. If my plastic is going down goopy, I just turn down the nozzle temp until it isn’t… I’ve come to accept that things often print better if I set the print speeds to be slow. It gives the layers more time to cool before the nozzle comes back around.
Thanks for another interesting point. It is faster than you are suggesting. My slicer settings for “external perimeters” is 25 mm/s and for “perimeters” is 40 mm/s. There are no other type of movements on these hexagonal structures.
I may try slower printing at some point, but it’s already a 7 hour print 😄
HUMIDITY
My guess is mechanical stress during the print.
Think of your print object as a lever. The attachment to the print bed is the fulcrum. The taller the object gets, the longer the lever arm and the more potential for movement, especially while the plastic is still warm and soft.
On the other end of the lever is the nozzle spitting out melted plastic. The melted plastic is sticky (PETG in particular is kind of like chewing gum at print temperature). As the nozzle moves across the printed surface, the sticky plastic pulls on the previous layer, exerting a lateral force (you can watch this happen during the print, it’s most obvious with tall thin parts). If there isn’t enough contact area between the topmost layer and the one below it (which in your case it appears those parts of the hexagons have very little contact with the layer below) then the top layer can be ripped off.
Basically the individual limbs of the hexagons are too thin, and the angles are too steep. As the print gets taller the whole thing will flex more, making failures more likely near the top.
That also makes sense. I imagine if there is a way to increase adhesion between layers that would help with such problem
How long has your filament been exposed to air? It looks like blobby wet filament to me.
2-3 weeks before I put it into a dry box with a bunch of silica gel
