How to work with PETG? Settings, caveats, etc

Question

We've been doing some printing with PETG filament on Ender 3 Pro printer and the result were awful:

Here are settings we used:

• Extruder: 240 °C
• Bed: ~70 °C (± 10 °C)
• Speed: 80 mm/sec

There are a few types of problems that we had:

1. Initially filament did not stick to the bed - those 3 items in the middle of the picture are example of this issue. This got fixed by increasing temperature of bed to 80 °C.
2. At some point a piece would get dis-attached from the bed and would move around together with the extruder around - two prints in the upper right corner of the picture were cancelled for this reason.
3. Models are very rough, like a cheaply made snowball - that tiny model in the upper left is suppose to be a cattle-bell. Could you tell?

Additional info

Filament that we used indicated

• extruder temperature 230-240 °C
• printing speed 40-90 mm/sec
• no info about bed temperature

Question(s):

• What are some optimal, tried and tested options for printing PETG? _{(Temperatures, speed, etc)}
• What are some caveats/difficulties of working with PETG to look out for? _{(For example, I've read that PETG likes slower speeds. Is that true?)}
• Is it possible that the model of 3D printer does not work well with this type of filament? _{(I don't have much experience printing so I can't know)}

Answer 1

Slow down!

80 mm/s is much too fast for PETG. Try 45 or 50 mm/s instead, even for infill, supports, and other less-visible areas.

Answer 2

The Ender 3 can print PETG alright - in some regards, such as warping and adhesion issues, even better than PLA. But you do need the right settings. 230-240 °C is too low, especially at the extremely high speed you're trying - you're going to get serious under extrusion and likely stringing.

My PETG settings are 80 °C bed, 250 °C hotend, and normal 30/60 mm/s speeds 40 mm/s print speed for everything, and lowering fan speed to 40 % or lower (ideally off entirely unless you find you need it). Full speed fan will prevent bonding, and is not needed to avoid warping like it is with PLA.

Also make sure you have the first layer set to print slowly (30 mm/s or less), and make sure your gap between the nozzle and bed isn't too wide. You also need the nozzle to be primed well before the actual print starts. A skirt can do this but I prefer custom start gcode to print a thick priming line at the edge of the bed. Mine is based on Ultimaker Cura's default but only goes one direction rather than reversing and moves a lot slower.

Answer 3

None of your prints look like they are sticking well to the bed. You didn't specify the bed material. For many bed types, you might have success with Aqua Net hair spray.

Like any material, if it isn't solidly sticking to the bed, the print won't be good.

This probably is not related to your problem, but you may need to reduce the drive gear pressure or "pinch" of the filament. PETG seems to be softer than PLA or ABS, and I've had problems where it was rolled out like pie crust by the filament feed gear to the point where it would not feed. Reducing pressure, reducing retraction, and increasing the minimum extrusion between retractions helped.

Answer 4

The real problem was that I damaged the nozzle (most likely while cleaning it) in a way that increased the size of the hole. So, too little filament was coming out of too big of a hole, which caused such poor models. Replacing the nozzle fixed the problem.

I do not remember the settings of the top of my head. Generally advised settings for PETG (whatever they were) worked fine.

Answer 5

I just made an account to point out that you will scorch your PTFE tube if you listen to anyone here telling you to print at 250+ C. I have done this, it is a bad idea without an all metal hotend.

Not a lot of dumb things on here will actually give you cancer, but cooking your PTFE-liner will.

Answer 6

I use a fine round brass brush, similar to what you would use to clean a gun barrel, to keep my nozzle clean. The brass is softer than the nozzle material, so it doesn't damage it, and the bristles grab strings easily - you barely have to touch them.

I'm using SUNLU PETG filament in my Ender 3. It sticks VERY well to the "Creality Original Ultra Removable Magnetic 3D Printer Build Surface". I'm set at 70 °C on the bed. Get your height set well. I had a ton of issues with nothing sticking until I got it dialed in. Now, it almost sticks too well. I often have to remove the magnetic sheet in order to get larger prints off it.

Answer 7

55 mm per second is the highest I would go with PETG. Cleaning the nozzle more often helps. Also check your PID for the nozzle temp, it could be inconsistent and PETG can be very finicky with temperature.