1) What country do you live in? (This is an important question - but I don't want to explain why - please update your profile location to indicate your country).
Austria
2) So can you explain the symptoms again? Does the head knock the part off the bed?
No, maybe it would have done if I let it go on.
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You say it's grinding into the part. Do you abort the print at that point? Or does the head just keep moving and moving with Z never moving and no more filament coming out? Or is it printing in the air? With the head above the part by a little gap but the filament isn't coming out?
Yes I abort as soon as I see the problem, it appears that at that point no more filament is coming out.
3) If you hold the z screw while it's printing the "failing" area you could feel if the shaft is spinning a small amount between layers.
I visually note a reference on the z-spindle, check it for change, I do not see it change.
4) I see you are printing with brim. Is that working? Or is the part lifting off the bed on the corners?
The brim is working ok and is not lifting at the corners.
5) What is your: print speed, layer height, nozzle temperature? (these 3 numbers combine to let me know if you are printing at reasonable flow rates - knowing only 2 of the 3 numbers doesn't help much).
I changed the speed from 50 to 150, layer height .1 to .25, temperature from Cura default (around 220?) to 240.
Notes.
1) While NOT printing this model I have successfully printed other organic models with all these combinations with predictable results i.e speed effected quality etc. Including extreme values on the same model for study.
2) Now the head is blocked and so I am truly stuck! The last time this happened I unloaded/loaded filament which fixed the problem but this time it is not working even after setting temperature to 260