PETG Collecting on the Extruder

Question

I have recently bought a spool of eSun PETG. So far I really like the filament. My only complaint is, I get lumps of charred filament deposited on my object. The slicer I used is Craft Ware and I have played with the Far Travel -> Elevation settings. I have noticed that this helps but then I have little to no adhesion to the print surface and my supports do not stick to the raft. Does any one know how to mitigated PETG from collecting on the extruder?

Answer 1

Different brands and blends of PET filaments seem to do this to different degrees. Esun's PETG is definitely one that tends to glob onto the nozzle. Basically, the nozzle plows through the top surface of the filament and lifts up some plastic, much like the bow of a ship lifting up some water at high speeds. PET's viscosity and stickiness seem to amplify this effect more than other filaments.

Some things you can do to minimize the globbing:

• Calibrate extrusion volume on the low end of what you'd normally use for other filaments (how you do this depends on your slicer)
• Use your slicer's "Z-hop" or "avoid perimeters" feature so you don't do travel moves across printed surfaces
• Invest in an anti-stick coated nozzle, such as are sold by Micro Swiss or Performance 3-d (these don't eliminate globbing, but they do reduce it and make the nozzle much easier to clean)
• Play with slicer settings such as extrusion width, layer height, and infill/perimeter overlap to reduce the amount of "excess material" that sticks above the print surface

Again, this is a common problem with PET blend filaments. Anecdotally, some brands seem to glob more or less than others, so switching to a different vendor may be worth trying if you want to do a lot of PETG prints.

Answer 2

For me, none of the classic solutions to PETG zits worked; these include extra retraction, slower/faster retraction, lower extrusion width, lower extrusion multiplier, avoid perimeters etc. It was especially disappointing to see lower extrusion multiplier making no difference whatsoever in reducing the zits, but only resulting in a mechanically weaker and even spongy result. What made all the difference is to disable z lifting during retraction which my slicer profile has enabled by default. This setting alone eliminated nearly all zits and most stringing (i.e spiderwebs).

Of course, the amount of zits and stringing will heavily depend on the particular filament you're using and the particular model you're printing.

Additional note: I was getting extra zits/overextrusion on a particular model I had that was exceptionally thin and tall when attempting to print with PETG. Lower extrusion multiplier made no improvement but weakened the part and resulted in spongy structure. I was successful in printing this part along with another part that was of similar height. I'm suspecting that printing the part alone but much more slowly to help with cooling would also succeed.

Answer 3

PETG strings at working temperature to different extents depending on brand. Some of the thinner strings are flying in the air due to the fan or mechanical stress, and are finally captured by the hot end. I feel, PETG has two modes

• Too cold: Less to no stringing, but sometimes underextrusion and weak layer bonding
• Hot enough: Stringing (from weak to strong) but good bonding

Things which do not help (at least least on my printer with direct extruder), but which I tried out individually

• Retractions past 1.5 mm on my direct extruders
• Reducing minimum distance
• Retraction speed 30 to 60 mm/s
• Z-hops
• Fan speed 30% to 100%

Things I have not tested

• Maybe minimum layer time could be increased

Things that worked

• Coasting seems the only thing which helps, but you still have very thin strings at sufficient temperatures

Other things to consider

• As mentioned the PETG brand has a certain impact
• The worst Co-Polyester I tested were (by far) the XT-Filaments (pink and green)
• All regular PETG filaments were better than XT in nearly every aspect, but still tend to string to a certain degree