3D printer destroys part by lowering nozzle

Question

I have a Lulzbot TAZ 4 and am using Lulzbot Cura for slicing, printing with HIPS.

Yesterday, I tried a print, only for this to happen:

It appears that the printer got most of the way through printing the part, and then for no apparent reason lowered the nozzle into the part (causing it to detach from the bed), raised the nozzle back up, and then to continue trying to print like nothing happened.

I thought maybe the G-code file got corrupted when transferring to the SD card (a single bit-flip could cause exactly this problem). So I generated the G-code again with exactly the same settings, and the same thing happened again but in a slightly different place and a few layers further up the model:

I have previously printed exactly the same model, only mirrored, with the same settings, and did not have this problem. I've never seen anything like this. Does anyone know what is going on?

Answer 1

This is my bet, based on cooling fan failure (I assume it was nozzle fan, not a heatsink fan), though honestly my practical experience with HIPS is zero. Without this fan heated material printed at high angles will definitely curl up, and even flat may be unstable. I suppose it happend, observing layer inconsistency on middle finger close to the nail.

Then, material could curl a bit and build up. Collisions with hotend could result in blob of plastic here or there, and then something bad happened (see @Jack State comment).

I also suppose that the whole print was detached from bed and rotated, because we see surprising shape across the middle finger, and unfinished index finger. Filament was extruded in random locations, causing more blobs, more curling and more mess. There are some gaps which look exactly like hotend run directly into them. I suppose that object rotated both horizontally and vertically. It could be even dragged by hotend at the end (e.g. filament was extruded inside the index finger).