I'm trying to hollow out this solid model http://www.shapeways.com/model/732444/37c490266b848c0a94a894 89cfd0a25b to bring down the cost. I'm trying to use 1.5mm walls, and I generated the attached STL. However, when I upload that to Shapeways, it just becomes a solid disk. In netfabb, if I run the Automatic Repair, it similarly just fills in everything. Are there primers out there on the web that people can point me at? Specifically, I'm trying to figure out why netfabb is squawking about my design. I'm not at all surprised I made a mistake, but all I get is a giant caution symbol and no details. I'm hoping there's a way I can get netfabb to tell me, "yo, this part here, this is bogus".