Here is the furnace body and the base after being poured and tamped. Look closely at the base and you can see the wooden rod used to form the drain hole, in case metal is spilled in the furnace. The refractory is setting up in this picture, and is a thick slurry of liquid. Too much liquid for "optimal", but it seems to have worked quite well, and was easy to pour and tamp.
Here is a close-up of the 1.25" pipe cast into the furnace body. The idea was that this would give a nice tight fit around the pipe, and reduce heat losses around the pipe fitting hole. In reality, it made the hole a nice size, but pulled out shortly after I started moving the furnace around. There was a very thin portion of refractory below the 1.25" pipe, which also cracked and fell off. Not a big deal to patch it up, but you can learn from my mistake and make the hole a little stouter.
A view looking into the top of the furnace. The concrete form was hot-glued to the styrofoam base, and it seemed to do an excellent job of keeping the forms in location, and also preventing slurry from leaking through around the base and forming air pockets. The slop that fell inside the furnace doesn't have to be removed, because the base was formed separately from the body.
This is a better view of the base, with the drain hole being cast in. The wood spar was removed after about 24 hrs of set-up, while the refractory was still moist and soft enough to remove it. You could probably just leave it in there, and it would burn up during the first curing session.
Here is a picture of the completed control board, ready to be mounted on the furnace cart. I didn't want to spring for a sheet metal enclosure, so just screwed everything into this piece of plywood, and hot-glued any loose components. It works pretty well, but I'm worried about a fire hazard should any molten metal spill onto the board by accident.
Here's the completed furnace, on a small cart I welded to hold it. My original plans were to make a much larger furnace, but this small one will be suitable for testing the refractory and construction techniques, before investing too heavily in materials. You can see the hair dryer and control board I use to run the rig. The completed furnace tends to leak flames around the base, where the base was formed separately from the tubular body. I plan to fix this with a thin layer of refractory mix to lightly bond the two. The same may be done with the lid to create a "keyed" fit, using some cellophane wrap and a bit of refractory patch.
