I built this furnace so that I could easily cast 3D printed parts into exact cast metal replicas.
With it I have cast high tolerance machine parts that required zero machining directly from 3D prints.
Here is our documentary demonstrating the complete Lost PLA process with this furnace: http://www.thingiverse.com/thing:82176
Download the PDF. Note that any image in the PDF is enlargeable if clicked (and you are online).
Note that this is more of an "instructable" than a "thing", but I think based on my successful Lost PLA 3D printed castings that it hopefully will have wide appeal to this community.
I have documented the Lost PLA process used with this furnace design here (as featured on hack-a-day): http://3DTOPO.com/lostPLA.