PETG is an interesting material, which has the ability to look really great in a variety of projects… But boy, it can also be a pain to deal with. Basically put, here are the three rules for getting a good clear result with PETG:
- Print HOT – My spool said 230-250c, but I only started getting good results at 255c or so. Build plate at 100c.
- Print THICK – Cloudiness comes from one of two sources, too much speed (more on that below), or air in the print. Printing with 100% infill, and thicker layers (even up to 0.2mm) provides less places for air to sneak in and cloud up the print.
- Print SLOW – PETG seems to go white/cloudy when it’s extruded too quickly. Keep in mind that you likely want to track the total volume per second (the thicker your’re going, the slower you want to move the print head). Be sure to check both the speed of your print, and infill. I aim to have a total print speed volume of 1.5mm^3 per second or so.
The whiter print on the left is PETG at higher speed, with 20% infill. The print on the right is the same spool of filament at 100% infill and a slower speed. Unfortunately for the right print, I had forgotten to slow down the infill speed.
If at all possible, print in orientations such that the printer is putting down as much in a single contiguous pass as possible. This stuff gets brittle when it cools, and so the print head can easily damage a part if it’s moving between pieces.
Are you seeing stringiness? The print head is moving too fast.
Is it trying to stick to the nozzle, where it will burn? That’s pretty much PETG doing what PETG does. Try to give your nozzle a good cleaning if possible between prints.
Be patient. I know a lot of people who say that each spool of PETG can be different, and since the stuff loves moisture, it can vary greatly depending on printing conditions. When in doubt, slow things down and try again.
Polishing – I was able to polish some using Brasso. I still need to try using toothpaste to see if that helps at all. I’m working on a larger piece to see how it finishes. The stuff is quite a bit harder than PLA, so it’s something of a chore to sand.
Here’s a successful print. The part is about half an inch thick, and we’re looking at the build-plate side of the print. This is before any cleanup or polishing.