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I have recently started printing with Polymaker's PolyMax PETG on my Ender 3 v2. I have not been able to get the layer adhesion anywhere near as strong as it should be. I would guess it is around 20-25 % of the strength in the XY direction. The parts snap easily along the layer lines under loads that PLA and nylon hold up to just fine.

Print settings:

  • 0.15 mm layers @ 35-20 mm/s
  • Hotend temp 245 °C
  • 4 mm retraction @ 40 mm/s
  • combing on
  • jerk control on
  • no cooling

I made sure to use a nickel-plated brass 0.4 mm nozzle. I have calibrated my E-steps and tried printing in an enclosure, but nothing seems to help with layer adhesion. I have made sure there is no debris getting on the filament as it comes out of the drybox and even tried taping around the heater block so there is absolutely no part cooling.

Any ideas as to what I could be doing wrong?

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  • $\begingroup$ Have you already tried a thicker layer height to see if that makes a difference? E.g. 0.2 mm? $\endgroup$
    – 0scar ♦
    Jun 12, 2021 at 6:19
  • $\begingroup$ Yes, and it makes no difference. A wider line width just leaves lots of blobs on the print. I think it is over extruding slightly. $\endgroup$
    – TreeBarkEater
    Jun 12, 2021 at 16:41
  • $\begingroup$ Maybe you misinterpreted the comment, I wasn't talking about line width; I commented on layer height. PETG prints better when layer height is not too small, I've mainly used 0.2 mm and printed kilometers of 2.85 mm without major problems. $\endgroup$
    – 0scar ♦
    Jun 12, 2021 at 22:49

3 Answers 3

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I had this problem with my Ender 3 until I changed to a different extruder and now PETG never has adhesion problems. Even 100 % fan is fine at 245 °C. I think the stock hobbed gear just slips on PETG really badly, giving underextrusion. Go slow, increase the flow to compensate, and possibly increase temperature slightly more. Or buy a decent extruder.

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  • $\begingroup$ Why would it under extrude if the esteps are calibrated? $\endgroup$
    – TreeBarkEater
    Jun 12, 2021 at 4:31
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    $\begingroup$ @TreeBarkEater: Calibrated under what extrusion rate? Actually pushing material thru hotend at print speed, or just moving it in the bowden? My best understanding of what I experienced was that there was just a lot of slipping under backpressure, and this is really bad for PETG if you're using linear advance since it needs a fairly high spring constant that increases the pressure (and thereby slippage) even more. Also, if you're not using linear advance, that will give rather inconsistent extrusion that also makes the layers adhere poorly. $\endgroup$
    – R.. GitHub STOP HELPING ICE
    Jun 12, 2021 at 4:57
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    $\begingroup$ One more thing: combing is bad for PETG. Because it's so sticky, moving over already-printed material without retracting tends to drag it, making a poor surface for the next layer to adhere to. Try turning combing off (or leaving it on but setting max comb distance without retract to < 1mm). $\endgroup$
    – R.. GitHub STOP HELPING ICE
    Jun 12, 2021 at 4:58
  • $\begingroup$ The OP is already printing pretty slow, the max recommend speed of the PETG I'm using (printed about 20 kg of 2.85 mm filament) is 55 mm/s, so I wouldn't call the OP's speed fast. I fully agree on using a decent extruder. $\endgroup$
    – 0scar ♦
    Jun 12, 2021 at 6:16
  • $\begingroup$ @0scar: it's not fast, but maybe fast relative to Creality's extruder. $\endgroup$
    – R.. GitHub STOP HELPING ICE
    Jun 12, 2021 at 13:29
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I got a roll of Hatchbox PETG and the prints are fantastic. Small test prints don't break along the layers even at higher fan speeds. The problem was the Polymax PETG. I took a look at the TDS for it and the impact strength on standing samples was only 29% of the standing ones. I believe the Polymax PETG just has inherent layer adhesion problems.

Please note that Polymax PETG isn't PETG, it's PCTG. I may try doing some firmware changes and printing it at 270 °C later on.

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The layer adhesion with Polymax PETG at 260 °C was great so I didn't go any higher.

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