Help with why 3d print has a big long hole?

Wondering if anyone can figure out why this 3d print (on a Prusa FDM) has a long strip of unprinted area on only one side? It prints ok on the identical other side, but leaves a huge gap on this side. I have the extension Solid Inspector2, and it says a-ok…
I eventually went back to an earlier version without the side indentations, and it prints ok.

mlbiv4.skp (1.3 MB)


You have some overhangs going on.

The top (longest one) is right in alignment with the gap in your first photo.

For comparison sake, I’d be curious to see an inside picture of how the two smaller indents printed out at the bottom of the inclined wall. Their exteriors are starting to get a bit dodgy too, but I guess the shorter lengths help make the span printable (?)

If no internal supports are being generated automatically for these ledges… then I think I’d add some in manually… and see how that goes.

I don’t know how much overhang you can expect to get away with on your printer, but perhaps this project is starting to answer some of that question.

The supports don’t have to be external (cut away) supports. You could build in triangular brackets underneath, and space them apart by some distance, to eliminate the longer span.

Maybe cut-down your model, and run some experiments to see how far you can stretch the shorter indents before they start producing print failures too. Back that distance off and apply it as the spacing rules for how close the brackets should be on the longer span overhangs.

Thanks for the reply; the overhangs are unsupported - one side printed ok, and the other side failed (tried twice.) So you don’t think there is an error in the model, but the print is failing due to the overhang?

Try changing the position on the printer, turn it 45deg or whatever is possible to fit the bed. It may just be that the head is moving in a different sequence on one end from the other. If it is aligned so there is a long run along an overhang it could fail.
One of the main tricks with this sort of printing is finding the optimum position for everything to work. More often than not it is not square to the bed or even flat to it.

Hi, @handyguy

I agree with Box about model placement and orientation on the printer bed.

I’d run some test prints to see exactly what happens at a small scale and without having to print your entire model as an experiment.

For checking print path direction and it’s influence on overhangs you could take your cross section and revolve it around 360° and see which direction it starts to fail in.

something like…

But that’s not to say that the support idea shouldn’t still happen (if it’s needed). I just like to base everything on the results of some test samples… and probably spend too much time messing around with things that way.

The unsupported areas in question are the other way round - the print starts from the flat tub bottom so the areas are supported from underneath. Using Zorro and section plane, I have cut the model down to the defective side and I will try printing that at a couple angles to the print bed.