Help with stringing and blobs

[Adventurehill1 0]

Printer: Anycubic Kobra Max with Capricorn Teflon Tubing

Slicer: Cura 5.6.0

Filament: Overture PETG

 

I have been having problems with blobs and stringing for a good bit now, I think it has to do with my retraction settings, but I'm not sure what to tweak. For some reason I am also getting a lot of plastic buildup on my hotend and nozzle. Any help would be greatly appreciated.

PETG SupportCalibrationCube.3mf

[Slashee_the_Cow 409]

Always convenient when I find someone using the same brand of filament as me 🙂

 

PETG is inherently stringier than PLA which does make it annoying. Though it's great stuff when you get it the way you want it (especially when you want to build something a bit flexible and nail the right settings, though that can take a bit of trial and error).

 

For plastic buildup on the hot end and nozzle, I would say: double, possibly triple check your bed levelling and Z offset. If there's even a tiny bit of a gap between the nozzle and the top of your layer, it's going to be more inclined to stick to the nozzle because it's touching the nozzle and not the plastic/build plate.

 

Now, as for your print settings, I'd recommend the following changes:

• Material > Build Plate Temperature to 80 (if you can). First layer adhesion is important a nice hot bed is much more attractive to the plastic... literally.
• Material > Printing Temperature I use 235°. The information guide which Overture (very handily!) throw in with their filament says 230-250 for the printing temperature and 80-90 for the bed so don't be afraid to turn it up a bit more than that.
• Material > Printing Temperature Initial Layer to 240°. I run the first layer a bit hotter with almost any material, again, it's an adhesion thing.
• Speed > Initial Layer Travel Speed to 80mm/s. It's great you changed the speed already, but I think you just missed this one. Don't know why it doesn't change with the regular travel speed, you generally always want it to be the same speed or lower.
• Speed > Print Acceleration to 500mm/s². The longer you give it to stick to itself and not the nozzle the better, and when it starts accelerating is when it's most likely to be dragged instead of stick.
• Speed > Travel Acceleration to 700mm/s². I've had printers accelerate so quickly on travel moves that they've pulled PLA which hadn't quite set with them... a pretty impressive feat (thanks for making your printers so fast it's stupid to use their whole speed, Creality) and PETG is going to be worse than that.
• Speed > Print Jerk to 6mm. Corners (and starts and stops) are where you're most likely to lose adhesion so slowing down the corners (but not so much it nearly stops) helps avoid that.
• Travel > Retraction Distance to 8mm. Been a little while since I've used a printer with a Bowden extruder but that's what I used. Needs to be retracted further simply than something like PLA because it likely won't all come anyway and needs a little extra motivation. And if you think that's bad, don't even try TPU.
• Travel > Retraction Speed down to 45mm/s. Stringier materials are sort of like a rubber band behind held at one end (the hot end, in this case). If you yank it, you'll probably just break it (and if you break the connection with what's at the nozzle, it's not going to retract), but if you pull it slowly, it'll come with you.
• Cooling > Regular Fan Speed to 100%. You want this stuff to set as quickly as possible.
• Cooling > Initial Fan Speed to 0%. The first layer is an exception to the above rule (because the longer it's hot the more time it has to adhere to the plate).
• Cooling > Regular Fan Speed at Layer to 3. This is a combination of the above rules: needs to properly melt and adhere at the start, needs to properly set and stay in place as quickly as possible shortly after.

There's also just that due to its stringy nature, it will leave more strings behind than something like PLA, and that's unavoidable. But hopefully we can get it mostly blob-free.

 

Hope that helps.

[Adventurehill1 0]

I printed a simple calibration cube, rotated 45 degrees to test supports, and something very strange happened. I used the settings you recommended as well. You can see in the pictures that the top printed fine, but everywhere that I had support it seemed to under extrude and string. This almost seems like a slicer/gcode error?

[Slashee_the_Cow 409]

12 hours ago, Adventurehill1 said:

I printed a simple calibration cube, rotated 45 degrees to test supports, and something very strange happened. I used the settings you recommended as well. You can see in the pictures that the top printed fine, but everywhere that I had support it seemed to under extrude and string. This almost seems like a slicer/gcode error?

Wish I had a good answer to that (and if anyone has one, I'd love for you to jump in and supply it), but I'm not sure if there's a way to avoid that, in my experience it's an inherently PETG thing. If you have Support > Enable Support Interface on (and it usually is by default) try turning it off (assuming your support is dense enough that you can bridge the gaps, but unless you've turned Support > Support Density way down it probably is) and set Support > Support Z Distance to 0.

 

Yes this means you're removing the support right from the model (if you use a pattern like Zig Zag it shouldn't be too hard to remove) which might cause a scar, but it also means that the model is sitting directly on top of something rather than having a chance to sag down to support. And trust me, it's a lot easier to file down a line or two from removing support than trying to sand a whole layer to get rid of a support interface. Unfortunately power tools are cheating and you will catch yourself out (my Dremel, using the highest grit disc I have, at the lowest speed, will melt the plastic and deform it).

[PizzaTijd 13]

Drying your filament might also help. 'wet' materials can also cause unpredictable/worse printing behavior.

Edited February 28 by PizzaTijd

[Slashee_the_Cow 409]

1 hour ago, PizzaTijd said:

Drying your filament might also help. 'wet' materials can also cause unpredictable/worse printing behavior.

Nice save! I have a filament dryer so I always forget that one. Materials like PETG or TPU are hygroscopic (they absorb moisture from the atmosphere) and when they're "wet" they really don't print as well because they're runnier and the extruder can't grab them as well, nor can the nozzle direct its flow as accurately.

• Some people store their filament in resealable bags and put desiccant in them - you can buy it by the bottle, and get stuff that changes colour when it's absorbed about as much moisture as it can. When that happens, you just need to put the desiccant in the microwave on low for a little while until the colour changes back.
• You could buy a filament dryer - I went for this option because I'm lazy and know I'd never get around to checking and "recharging" desiccant. Just turn it on and put your filament in there for a couple of hours before you start printing - many have little holes you can open to get the filament out so you can print it while it's in the dryer (you still need to give it a bit of drying time before you start printing).
• Some newer (and often fancier) ovens have a setting designed specifically for drying things.
  • Some microwaves do, but you don't want to put your filament in there, just desiccant.
• About all that's left is the cheater's way - heat your printer bed up to about 50°, lay the filament down on top and cover it with a blanket. Give it a couple of hours.

Something I wondered when I started using PETG and TPU was "how long will it last after I pull it out of its vacuum sealed (and moisture free) bag" or "okay, so I dried it, how long until I have to dry it again?". Answer's not so simple. Plus I'm really over-cautious. Depends on your environmental conditions - Australian summer, 100% humidity anyone? I'll trade you.

• Store in resealable bag with desiccant: it's pretty simple - unload the printer whenever you've finished printing with it and put it back in the bag. Should last long enough out in the open for any decent print. If it's properly dry, maybe a day or two, as I said, depends on environmental conditions.
• Dryer: I don't actually know because I haven't tried, but if I haven't printed with it within the last 24 hours or so, I'll give it a bit of time drying (because it's so easy, it'd probably last a couple of days being dried again) before I start printing (my dryer's display tells you the internal humidity). I usually print while it's in the dryer (and leave it on).
• Oven: Probably two or three days. Ask @GregValiant, he's the one with the fancy oven.
• Hot printer bed: It's not so great because while you need the blanket to keep the heat in, it also traps the moisture so it's not as effective as the other options. Should give you at least a day or two 

Edited February 28 by Slashee_the_Cow

[Adventurehill1 0]

3 hours ago, PizzaTijd said:

Drying your filament might also help. 'wet' materials can also cause unpredictable/worse printing behavior.

Thanks. I have a filament dryer, but maybe I let the filament sit out for too long between drying. I'll try it.

[Adventurehill1 0]

On 2/27/2024 at 11:44 PM, Slashee_the_Cow said:

set Support > Support Z Distance to 0.

 

 

Do you think I'd be ok to set the z distance to 0.2? The lack of a support roof seems to have cured my problem, but the support is difficult to remove.

[Slashee_the_Cow 409]

9 hours ago, Adventurehill1 said:

Do you think I'd be ok to set the z distance to 0.2? The lack of a support roof seems to have cured my problem, but the support is difficult to remove.

Can't hurt to try. Remember: small scale testing is your friend.