PLA and PETG warping and x,y shifting - solved but might prove helpful to others
tldr: The warping causes the print head to hit the warped up side and slide off the current position on the band. This means the printer thinks it's printing somewhere and reality it is printing in a different x,y coordinate. Resolution: clean with 99.9% IPA (not 90% as documentation suggests) on a smooth base (not textured for PETG) and adjust the tension on the bands so they are in the correct range.
The blurb:
I've tried to print this 200 x 200 x 15 mm piece. I designed it myself - basically some calligraphy. Initially with PLA it seemed to have shifted the x/y position twice during the print. The bottom of the piece exhibited warping (edges turned up). But what puzzles me is that the print seems to have just continued at a completely different x/y position (this is obvious since the stringing has occured where there was no base support after the shift.
I then tried PETG on a textured base thinking the warping would be less of an issue at least. Turns out it also warped but this time only one xy shift. Again - you can see the printer continued to print completely away from the initial position...
In both cases the middle of the bottom of the piece was firmly in the correct starting position....
I should add that printing a benchy (which is taller than the thing I'm trying to print now) has shown no issues at all...
I haven't yet tried this with PLA but the PETG seems to behave now with a strong adhesion to the smooth sheet.