I'm trying to print this thing: http://www.thingiverse.com/thing:1385312 but the preview shows it's trying to fill in the center tube of the "track.stl"
I've mucked with the file a bit and tried different variations, but it still tries to fill in the middle of the object (which needs to be hollow).
Previously that happens when there's a missing face or something, but I can't find anything in the appropriate areas. (There are a few issues, but nowhere near the problem spot).
I've also tried some very small cap-type things, 2mm or 2.2mm diameter hollow in a 6mm cylinder about 10mm tall with a cap. The open-ended cylinder is printing closed @ 2.2mm and @2mm it was printing more like .7mm.