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I have an STL that has a flat surface which should contact the build place when 3D printing. The model has an unknown rotation. How can I rotate the 3D model to be flush with the build plate?

I am very comfortable with OpenSCAD, and I can use it to rotate the STL if I know the correct angle. Is there a tool that will let me analyze a single face (triangle) of a model to determine it's normal? If I can even get the coordinates from 3 points from the desired face I can calculate the normal and use that to calculate the rotation vector.

Jared Deckard
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  • I made a little bit of progress: Meshmixer's "Mesh Query" analysis tool allows me to select individual triangles. The "Triangle ID" it shows is a 0-based index to a "facet" of the STL file in ASCII mode. It looks like the normal of the 3 vertexes is already computed for me. I am going to have to do this several times, so if there is a better way I am open to suggestions. – Jared Deckard Feb 06 '18 at 05:01
  • I needed to get something started on the printer so I just imported an STL into OpenSCAD and started guessing values for the rotation vector. Since I had a large flat surface, I was able to use orthogonal view and the static camera angles to align the model to each axis. It took about 6 passes using 2 decimals of precision to get it to the point that the slicer treated the bottom as a single layer. That took 5-10 minutes per STL. Doing this 6 times was pretty manageable. Much more and I definitely would have probably done the math and scripted the process. – Jared Deckard Feb 07 '18 at 16:40

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Some tools like Cura or Repetier Host have slicers that analyses and tell you if it is ok to print or not. Both of them allow rotations.

Hola Soy Edu Feliz Navidad
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    Cura's rotate tool has a "lay flat" function! I just had to manually get the rotation in the general direct and it was able to rotate it the rest of the way. Thanks! – Jared Deckard Feb 07 '18 at 16:56