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What is the best technique to improve removing PETG from the print bed?

PETG is known for sticking well to the bed; so well that it does not need a heated bed. If it weren’t for printing other materials, I would try printing directly on the glass bed instead of a build surface. However, the build surface may help protect the glass from excessive force.

To reduce how strong the PETG sticks to the build surface I’ve reduced the bed temperature to 35 °C. It is easier to remove the skirt and brim by heating the bed up to 90 °C, so that the PETG is soft. However, if one tries to remove the printed object at 90 °C, the printed object is like to distort and ruin.

I did sharpen the putty knife on the top side only. This helps, but it still takes excessive time to remove the print job and clear the bed. The excessive force on the bed from the putty knife seems to increase the need to level the bed. It also seems to affect the flatness of the build surface.

I’m looking for techniques to make it easier and less time consuming to remove the PETG print from the bed.

P.S. Additions after input from answers.

  1. Added keeping the initial Z-height high enough to keep adhesion to the bed from being too high. This resolved the adhesion to the bed issue, but seemed to make adhesion between layers worse.
  2. Set hot end to 230°C for first layer, then increased hot end temperature to 250°C for better adhesion between layers.
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  • $\begingroup$ You might want to try a flexible bed liner, spring steel ones can take the temp. I've also used two layers of masking tape, which works quite well, but takes more effort. $\endgroup$
    – dandavis
    Nov 13 '20 at 20:49
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Playing around with the nozzle height will help: back it off until just before you have first layer adhesion issues. Don't jam the filament into the bed as you might for ABS. This helps with small prints. However, my experience has been that if you have a large enough continuous contact area (i.e. more than a few square inches) with the print bed, there will be problems getting the print off. So I still use painters tape (in case I have to rip the print off with force) and glue sticks (so that I don't often need to) on my aluminum print bed as I've found that makes it much easier to deal with without damaging either the bed or the print.

You can also try dialing back the heated bed temperature a bit (I think I've got mine set to 70-75c for PETG) but that also doesn't eliminate the issue with larger prints. Also, if I lowered it too much I had problems with first layer adhesion on any size print.

I also have a glass plate that I use for ABS, which I don't use with PETG. I've read too many accounts of it sticking too well to glass as well (to the point of the plate being destroyed) and didn't want to try using the amount of force on it that I sometimes have to when removing a PETG print. I also considered trying BuildTak but read accounts of similar issues with it and PETG. So I stayed with what's been working for me: tape and glue sticks.

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Correctly level your bed. Seriously, that's the answer. PETG does stick well, but it only gets difficult to remove if you're smashing the first layer against the bed with a nozzle that's way too close. With the bed leveled properly - using feeler gauges or test prints and a sub-0.1-mm-precision caliper - I have no trouble taking PETG prints off a buildtak-clone bed. Glass should be easier.

If you already have PETG stuck to a build surface you care about and don't want to risk destroying it, try heat, or alternating heat and cold.

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  • $\begingroup$ Z offset may be an issue. Already use heat for residue. Leveling method:see 3dprinting.stackexchange.com/questions/470/bed-leveling-method/… $\endgroup$
    – Perry Webb
    Nov 12 '20 at 18:56
  • $\begingroup$ @PerryWebb: I don't see how that helps with the important part of leveling, which is about getting accurate distance between nozzle tip and bed, not just consistent distance between bed and gantry. Technically "leveling" is the latter, but in the context of 3d printing and especially here I mean the former. It's possible for the bed to be level but at the wrong height relative to the nozzle. $\endgroup$ Nov 12 '20 at 19:02
  • $\begingroup$ I use a feeler gauge to set the Z-height at the origin, then set the dial gauge to zero for that height. Next is setting the rest of the bed to zero. I can get it under +/- 0.02mm, which is about as accurate as the adjustments can do. Of course, changing the Z-height means leveling again. $\endgroup$
    – Perry Webb
    Nov 12 '20 at 20:34
  • $\begingroup$ Assuming you start with the bed level, you should be able to adjust the height just by turning all the adjustment screws by the same amount (you can even compute that amount knowing the pitch). Did you try measuring single-layer tests prints' thicknesses? $\endgroup$ Nov 12 '20 at 21:00
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Try to lift the nozzle more than you'd do even for PLA. PETG sticks really well to the heated bed. If your bed is already well leveled you can adjust the nozzle position in Z by using Z offsets directly in your slicing software (AFAIK, Cura needs an extra plugin for it, Prusa Slicer has it built-in).

If you have done everything correctly, the PETG model should come out almost by itself just by letting the bed to cool down naturally to 40ºC approx. Be patient.

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    $\begingroup$ Raising initial Z-height was the solution from the previous answers. I printed with the bed temperature at 30°C because, with a build surface on the glass, higher temperature promoted adhesion to the surface. $\endgroup$
    – Perry Webb
    Nov 19 '20 at 13:06

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