3D printer destroys part by lowering nozzle

2

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:

Failed print 1

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:

Failed print 2

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?

Jack Stade

Posted 2021-01-23T05:38:25.853

Reputation: 23

Did you just re-generate the G-Code? Or you have inspected the the G-Code? I suggest to use Cura's PREVIEW and use right and bottom sroll bars to track the head movements. Do you use any plugins for Cura? What about the hardware? If your Z axes go fluently up and down? This printer builds up to 250mm, and model is much lower I guess ... but is it possible that this could be mechanical accident like the top of a carriage hitting into something? – octopus8 – 2021-01-23T06:46:22.533

1Considering the brown goo, this could have been caused by a blob of filament stuck on the outside of the nozzle and tore of the rest. What makes you say the nozzle dug lower into the part? Have you observed this? – 0scar – 2021-01-23T13:57:57.613

1The G-code seems to be fine. I've printed a model with the same height before, so I don't think it is a problem with the hardware. I didn't think that a blob of plastic could be hot enough to tear through already cooled layers like this, but looking at the print again it seems possible. I realized that my cooling fan was stuck and probably wasn't running on either of these prints, so maybe the nozzle overheated or something. – Jack Stade – 2021-01-23T21:23:38.750

Too less cooling on small layers doesn't allow the material to set properly, in combination with a blob and curling of the layers you would see this. Hence my question if you saw the nozzle go down yourself, so I'm not referring to the G-code. – 0scar – 2021-01-24T23:42:55.050

Answers

0

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).

octopus8

Posted 2021-01-23T05:38:25.853

Reputation: 722

Seems reasonable. I hadn't though about it rotating up as it moved. I fixed the fan and it seems to be working now. – Jack Stade – 2021-01-25T00:22:33.697

I liked the detective work here. Thank you for all clues - and for accepting the answer. Case closed. – octopus8 – 2021-02-02T04:05:48.127