Just started to test the waters and mess around with some 3d design for my own fun. I created what's essentially a basic pint glass in SketchUp that seems to look fine, but when I uploaded it to Shapeways it looks like it's totally solid (no space in the middle for where you'd pour your drink). Is this a common thing/did I mess something up? Not sure if this is a Shapeways issue, Sketchup issue, or a me issue. Probably a me issue.