Hoping someone with more experience might be able to help me out on this one... I'm ready to print a (roughly) dome-shaped sculpture I generated via Autodesk's 123D Catch app. The model's already been hollowed out to minimize the material volume, but when I send it to Shapeways in preparation for printing, the underside of the object gets completely filled in during the file conversion process. The filled-in version is way too expensive for me to actually order. I checked the original model in Mesh Mixer to make sure it wasn't a glitch in 123D Catch, but it's just as hollow there as in the original app. So I'm clueless as to what the problem is. If anyone has any insight as to what's going on and how I might be able to fix it, I'd really appreciate it. Thanks!