First Layer Inconsistent  

Re: First Layer Inconsistent

It looks like your Z level is too low. This may be because the Z level is calibrated without tape on the bed.
My tip is to remove the tape for it's not needed. Then wash any glue from the tape with a suitable solvent.
Then wash the bed with detergent and water.
Instead of tape, you usually use a window detergent (Windex) on the bed. Then there should be no problem printing your PETG details.

Re: First Layer Inconsistent

I've never printed PET, but have rolls laying around I'll eventually try. I'll presume you are using the Prusa defaults for bed and filament temps, print speeds, etc. And doesn't PET want a much warmer bed than 60c? Tape insulates too, so you need to go even warmer than normal. Try 90c. Also, PET should extrude just fine at 240c, and doesn't need 260c (which is hard on the hotend).

It's really hard to tell if the layer 1 thickness is correct since the PET isn't sticking well. But the photo shows places where it might be too thick, other places where it looks okay.

As with anything else, how did you apply the tape? Did you use your hands and press the tape down with your fingers? Or did you use a litho roller? Fingerprint oils stay on tape as well as the PEI sheet.

Re: First Layer Inconsistent

@RHDreambox: Yes, the problem is that on some parts of the bed the Z is to low and on the other just fine. So if I increase distance it will be fine there but not good where it actually was.

I have contacted Prusa telling them that when I mounted the heating bed, some of the screw chamfers where not deep enough so that the screw head was surging the bed. I have deepen the chamfer, however as I don't have appropriate tools I may have done a bad job. But the screws are now partly ok.
So it could be that the bed is uneven from beginning on.

The guy at Prusa told me to take everything apart and see if all is straight. No need for that, I know its not.

However, it still should have some lack or room for little height difference and still be able to print properly.

@Tim: I press tape with clean towel down. So fingerfat not an issue.
According to Matterhackers, the PETG needs 240-260 approx. and no bed heating at all if used with blue tape. So I tried both.

Another issue with PETG is that it sticks very well typically, so if you use it without tape, it will most probably damage the pe sheet due to strong adhesion.

I will try now to identify the places where there is not enough clearance and put some aluminum foil under that place to equalize. But that is not a good solution. I think it all comes down to Prusa to send me a heated bed that did pas quality control.

Re: First Layer Inconsistent

Octoprint and Prusa Mesh Leveling plugin is a great tool for adjusting an uneven bed.
I am writing almost exclusively with PETG and to that I only use Windex.

Re: First Layer Inconsistent

I just printed a few small PETG items... I am impressed by just how sticky it is on bare PEI, Wow! is an understatement.

Just pulling the cleaning strip my usual way delaminated the PEI. I'm glad my parts were only 1 mm width contact patches. Anything else would have been trouble. From now on any time I load PETG I'll use glue stick on the bed to reduce adhesion.

Re: First Layer Inconsistent

I have printed a lot with PETG and it can be a tricky material to print well, IMHO.

Print surface:
In my opinion there's no reason or benefit for printing on painters tape, the Prusa PEI bed is perfect for PETG.
For preparation you want it to be clean enough to stick, but it can stick too well too!
When the bed was rather new PETG stuck very easily and well, and I used to brush off dust with my bare hand with the intention to deposit a tiny bit of skin oils to reduce adhesion. Later I had to wash the bed with soap to increase adhesion again.

First Layer:
PETG is very sensitive to Z-level, and it can be tricky to get it to stick just right. Before starting a print, I do a small test square to set the Live-Z to the point where it sticks and the extrusions are JUST welded together.
The Prusa presets are pretty fast, and I like to reduce the speed for the first layer to 60...80% with the TUNE setting, and print at 80% for the rest of the print. This helps a lot with the first layer and improves print quality for the rest of the print.

Filament:
PETG oozes, creates blobs easily, and can be very stringy. Keeping the filament in a drybox with fresh Silica gel improves all these. Since I keep my PETG in such a box, stringing is virtually gone, the zids in the surface (water bubbles) as well and oozing and blobs are greatly improved.

Print bed leveling:
Different issue, but since PETG is so sensitive to Z-Level I would start with a smaller print, and get that right.
You will have to get the bed flat (within reasonable limits) to print really large.

Good Luck!

Re: First Layer Inconsistent

seems abit high temp to be printing at.

Re: First Layer Inconsistent

[...] Another issue with PETG is that it sticks very well typically, so if you use it without tape, it will most probably damage the pe sheet due to strong adhesion.PETG prints just fine on the PEI sheet without glue or tape. You want to clean the bed, then use some Windex or a wipe of the hand to reduce adhesion somewhat. I have only had an issue using 3DXTech PETG which printed at 260C. I use glue stick before printing that stuff. With every other PETG at < 240C or so, no issues just using Windex and a wipe before printing.

I will try now to identify the places where there is not enough clearance and put some aluminum foil under that place to equalize. But that is not a good solution. I think it all comes down to Prusa to send me a heated bed that did pas quality control.
If you are under warranty, take pictures of a straight edge laid across the bed with a flashlight shining from below. Try from each corner diagonally. If light is shining through, it'll be obvious you've got a warped bed. Contact Prusa online chat and send the pics. They did not hesitate to send me a new one once I demonstrated the problem.

Re: First Layer Inconsistent

I print lots of PETg and direct onto the pei sheet with no problems.
PEI sheet cleaned with window cleaner and a scotchbrite pad (pan scrubber). Hot end at 230 to 240degrees C, Bed at 80 Degrees C. speed about 35 to 40mm/s. I alter the first layer speed to 25mm/s no fan then 50% fan from layer 2 or 3. Also first layer extrusion width made a little wider to fill out the squish area to reduce the line effect.
Leave the print to cool before removing from the sheet, this prevents the pei being damaged