I am trying to modify this thing. It's prints OK, but there are some design choices I don't like, so, since the previous makers uploaded their source files, I tried my hand at Sketchup.

My latest round of changes have produced a weird phenomenon, and I'm not sure how to describe it. The slicer sees the GCODE as I intend, but for some reason the printer is printing something different than what the slicer is showing me. I am primarily concerned with the top of this case, but the base does not have the additional screw holes I made, so the phenomenon, whatever it is, is not limited to a single part.

  • Sketchup v17.2.25555
  • Cura v3.0.3
  • OctoPi/OctoPrint 1.2.7
  • PrintrBot LC custom
  • Grey Inland PLA+ @~180C, bed @~60C (my temps are higher than the software thinks they are, so I have to put the temp lower in the software)

You can see the parts in Sketchup:

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The corner on the left was giving me no end of trouble! I left it with a messed up hole because I could more easily clean it up with a drill bit than spend another few hours futzing with that corner.

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This is in Cura, after I have sliced it. Looks fine to me! There is a bit of red in that problematic corner, but I only noticed that after the print came out weird.

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This is the output of the printer. Notice how the edge near the GPIO pins is shorter than the rest, and how the hole is inverted into a protrusion. This is the opposite of what I want, and the opposite of what I see in the other softwares.

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  • $\begingroup$ did you manage to fix your object (printout)? $\endgroup$ Nov 23, 2017 at 7:11
  • 1
    $\begingroup$ I redesigned it in OpenSCAD to solve the problem I was asking about. $\endgroup$ Nov 29, 2017 at 15:28
  • $\begingroup$ so maybe you can click accept ;) $\endgroup$ Dec 20, 2017 at 21:27

2 Answers 2


first issue

bed inclination. it has to be heavy issue :)

if you have any other printouts then please reveal them so we could see if it's the problem

next issue

inversion of hole into solid object

i would say it's caused by wrong calculation of normal vector to some face(s)

algorithm uses normal to calculates what is "inside" and what is not

it's hard to say if it's an issue of

  • object itself
  • application in which you modify it (even if duplicating or joining with other objects)
  • slicer engine

to fix the issue, you can try edit your object (recreate this hole)

but first - definitelly i'd align your bed properly ;)


after closer look i bet it's the issue of bad object. it looks like pointed line is kinda remnant of some operations made on object in the past

in other words - it's possible place where normals are reverted and doesn't "create" inside but outside

all above this line is reverted. part of body disappeared and part of hole appeared

this is the issue for sure!

enter image description here enter image description here

  • $\begingroup$ As far as bed inclination, I guess that's a joke? I've printed other things that print flat just fine. For example, the bottom part to this top part. Getting back to the main issue, I figured it was related to that corner. I don't think I have the skills to fix it, so I think I will just make the object from scratch. $\endgroup$ Oct 31, 2017 at 18:40
  • $\begingroup$ @YetAnotherRandomUser Yes, There are some extra lines inside your draw like darth pixel indicates with the arrows and there are a lot more. Those lines provoques cura, slic3r and simplify3D to create double walls, doble faces, invalid shapes and over extrusion. $\endgroup$ Nov 1, 2017 at 6:45

Looks like you are over extruding.

check out this visual guide for example (I like it a lot):


For the protruding thingy, it seems (as the other hole is filled up with over extruded filament, it seems) that it's the "hole" printed. For the rest of the "wall" where that hole should have been, it seems it was just not printed. What size is it (if too thin, the slicer might just discard it, doesn't seems like it but you didn't tell nozzle size etc).

I don't know, but I think you should start with calibrating your machine first so that you actually can print small holes like that.

For the missing wall, what does the slice result look like?

  • $\begingroup$ Thanks for the tip about overextruding. I'll look into your link. However, that's completely unrelated to the issue of the question. $\endgroup$ Oct 31, 2017 at 18:43
  • $\begingroup$ Could have been for the protruding 'hole' IMO but yes, it seems there is some problem with the model that makes the slicer invert volumes or something. $\endgroup$
    – Valmond
    Nov 1, 2017 at 11:09

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