MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
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That's an interesting mounting problem, how about make a difference between the fan and screw head to give more clearance?
in that case the walls can be thinner at the screw corners but if it's thick enough it may work
actually take a look at the full code in githubhttps://github.com/sherifeid/3dobjects
it should be more complete