This is doing my head in … It happens only with this particular piece ( a 20 cm diameter pinion). All starts well but after 30 layers or so the top layer is translated by around 10 mm. I print PETG with an airwolf hd2x on a heated tempered glass plate. The glass plate does not seem to move (at least not 10 mm). Any help is welcome.
Looks like steppers are skipping steps. Had this on my i3 clone and sorted it out by calibrating the drivers correctly. Usually happened after a good couple of layers when the motors and drivers get sufficiently hot.
Show me a picture of the printer
@Michael_Scholtz
missing/deleted image from Google+
@Jan_de_Jager That sounds logical. How did you calibrate them ?
What controller do you use and do you often do long prints. It can be stepper calibration. I thought maybe the size and at a point something touches the print head but unlikely in a vertical z Axiz Machine like that. Try and modify the print to just the outer ring gear so it prints the outer size but in less time. It will show you if the machine has an issue with the size or if it’s related to the time printing. Maybe also check the machine gears and belts are all tight as it should be.
Most probably overheating stepper causing it to skip steps.
Try lower the speeds, and use a fan on the controllers
this started to happen to me a while back on my Wolfstrap and i found that 3 of my grub screws that attached my lead screws to my stepper motors were totally loose.
I would start checking any thing with a grub screw to see if they are loose.
Stepper missing steps. Motor driver probably getting too hot.
I don’t think this is your problem, but I had a problem like that on a delta where the bowden tube caught under one of the carriages, pulling on the head. Always seemed to happen after I walked away.
Try printing slower.
Let us know what you find, hopefully our suggestions gives you a starting point… just dont give up, the “ah-ha” moment is totally worth it… 
It seems that the honeycomb infill cause problems for large pieces. I restarted the print with rectilinear infill … let’s see what that does. This would explain the steppers heating up since it demands a lot more movement