Cupola Furnace

There has been a bit of interest on here in the small homemade alu furnaces but I was wondering if anyone has any experience with usable amounts of cast iron?

Like this sort of scale furnace, still realistically doable for a group of serious diyers.

http://www.youtube.com/watch?v=xGLHFoa-9Tg

"kinda like throwing gasoline on a fire" obviously the non-sense monger that spewed that didn't learn a great deal from that pour... lol
ive melted aluminium and its worked reasonably well (Lionel Oliver style setup) but iron is a whole different ball game. if i had a few more lads locally who were interested i certainly think it is do-able but it aint easy.
small home brew cupola furnaces seem to have a tendency to collapse and i have been put off by a lot of failed attempts. i guess im just waiting for a good repeatable design to show up...
there are so many smart lads on this forum that it must be possible to come up with a good cost effective design that can withstand multiple melts.