Ghost in the Machine....Anybody ever seen this happen?

[Jules]

Okay, so I'd printed a tall thin-wall box, and it came out dandy, but I wanted to add a locking mechanism to it, so I quickly reworked it, sent it to print off the SD and went to bed. Got up the next morning and found this:

hairyprint.jpg

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The print looked like it seriously needed a shave! (And those little suckers were sharp!)
The funny thing was, sometimes the little broken threads were inside the box, and sometimes they were on the outside wall, but never in the same place on both sides at the same time. I was running off the SD because we were having some storm activity in the area - could that have been caused by mini power fluctuations?

All the other settings were the same for the two boxes, the only difference was that the first was printed over USB, and the second one was SD. Same spool of filament used in both. And the next day, when i reprinted it, (over USB) it came out fine.

(And i just noticed that all the fuzzies are on the X axis, the Y deposition is fine and smooth with the exception of two bumps.)

What the heck could have caused that?

[rsilvers]

How many perimeters, how much infill, and how much infill overlap?

[Jules]

One perimeter, zero infill, zero overlap on those. The design was for 1mm thick walls, and when it was sliced in S3D, the program interpreted it as two separate thin walls, exactly 0.4mm thick (nozzle extrusion width setting).

So basically the way it printed was as two thin walls side by side, with a 0.2mm gap between them.

I did increase the size of the walls to 1.2 mm with 1 perimeter in the final prints, with 20% infill that connected the two walls, because I wanted that stability.

Think the two thin walls were the problem on the fuzzies?

[rsilvers]

I keep Simplify set on between 3 and 6 perimeters.

What program did you model it in? Seems like the walls were not solid in the STL files. Look at the g-code preview and see if you see anything.

[Jules]

Rhino. They were solid.....I think that since i let Simplify use just one perimeter, and the total designed wall thickness did not allow for three 0.4mm lines side by side in the space allotted, it just dropped the infill.

(I probably told you wrong earlier, I had chosen 20% infill for the whole print, but Simplify ignored it in those thin walls because the space between the perimeters was less than a thread width. There was no infill on the one that first printed either, and the walls came out okay, but without infill, they could be separated at the top. One of the reasons I increased them in the final design.)

I still can't figure out though why it worked perfectly once and not the second time. Same exact settings and parameters.

Oh well....maybe we can catch it one day. Thanks for the ideas - I'll watch the thin walls a little more closely in the future.