Hi Marco,

I know I'm coming late to this 3D printing party. I have had three 3D printers and have also used multiple online services. For the most part, voxelization is not required when coming from MoI as long as you object is a single solid. You can add wall thicknesses in MoI or OnShape after the fact. Export as polys DOES NOT have to be as fine as you show, as the typical printing resolution isn't all that fine -- even though they say it is there is a "blurring" effect when you 3D print.

3D Coat is good if you have poly models created in non-solid modelers, where you can voxelize and be sure you have a solid. As someone earlier said, Shapeways (a great company for this sort of thing) has a 1M poly limit per object. The 3D printed cannon I shared before had lots of issues and I used Autodesk Netfab to help fine tune the wall and part thicknesses as well as detail resolution.

I would suggest starting on something simple, like you've shown. Just cut down on the number of polys coming out of MoI and you should be fine. Shapeways will alert you if a model in non-manifold and many times it will try and fix it for you.

Again, MoI is *great* for 3D printing and is one of the main reasons I started using it. Surface modelers are just too hard to control. Solids are the way to go. HTH.