Odd print failure - suggested causes?

[cobnut]

Here’s an odd one I’ve not seen before. I was printing the Faceless model (https://pinshape.com/items/6230-3d-printed-faceless-v2) and once the legs were underway and looking good, I left it. I came back a few hours later to find this:

What the heck happened to his left arm? (His head is incomplete because I stopped the print, the legs are missing because I was rather “enthusiastic” in removing the print, given that it was junk).

The weirdest thing here is that the rest of the model at the height where the arm is crazy is completely fine, and the arm begins printing normally again quite suddenly. I’m struggling the find a reason that would affect only that part of the left arm, while leaving the rest of the model perfect.

The only thing I can think of is a corrupted gcode file (the preview in S3D is fine), but it’d be a very specific corruption just to affect this one area.

Any ideas?

[wirlybird]

Looks to me like it moved somehow but hard to see in your pictures. Looking at the original model from the left side the arm is straight and lined up with his back. Hard to tell though. Maybe the model is corrupt at that spot?

[cobnut]

Ah Ha! I think you’ve got it @wirlybird! The lower part of the left arm and sword are not aligned correctly, it looks like they’ve rotated about 20-30 degrees from where they should be, so the “mess” is just the result of this lower arm part being loose (but not fully disconnected) and eventually the movement just happens to allow the print to get back on track.

Looking at where the model snapped off on the legs, what I thought was just my own brute strength snapping it, looks maybe now like a brief underextrusion or other flow interruption making the model weak at that point. This is (perhaps coincidentally, perhaps not) the point at which the left sword has minimal contact with his leg, so it looks like the sword was left only being attached by a mm or so of plastic, allowing it to move.

Not sure what caused the weakness at that point - the rest of the model looks absolutely fine, the reel is running smoothly, etc.

Anyway, problem solved! Thanks!