PETG lifting up on large prints

[Tim]

PETg shrinks, so it really is quite difficult to get it to stay down in the corners. The larger the surface you're printing in PETg, the harder it's going to pull when it shrinks.

Printing a very large brim can help a bit. I have managed to keep corners from completely ripping off the bed this way, although they were trying hard.

The other thing that helps is keeping the fan off, since the fan cools the print near the surface and accelerates the shrinking.

Probably it's a lot like ABS in that if you keep the whole thing hot enough in an enclosure, you can avoid having it shrink until it has finished printing. I have never tried using an enclosure, so I can't really say how well this works. People who work with ABS tend to make enclosures, because the problem with ABS is so severe. PETg does not shrink nearly as much as ABS, but it's enough to cause problems on prints that take up most of the bed area.

There are probably things you can do to the design that would relieve the stress of shrinkage, but I'm not a mechanical engineer and my few attempts to do something like that didn't appear to have any appreciable effect.

[ednisley]

posting your settings

As a GitHub Gist:
https://gist.github.com/ednisley/3e0076 ... 9a391dd332

Those are from Slic3r, but you can poke through them to find all the bits & pieces.

the first loop of the skirt which causes the problem

That's why skirts are so important: you want the ugly stuff to happen there, not on your part.

You may need a bit more time pressurizing the hot end = purging more filament before starting the skirt. I set the start_gcode commands to ram 20 mm of filament into the hot end to be sure it's filled and ready to go; I don't know where S3D tucks those settings.

print with raft

As nearly as I can tell, a raft was vital for older printers with poorly aligned / non-flat platforms. IMO, rafts are completely unnecessary for an M2: I just build the part upward from the platform and move on. Other folks surely have different opinions, though.