So, you want to build your own foundry ...
These two books should be very helpful in showing you how:
The Complete Handbook of Sandcasting - C.W. Ammen, TAB Book 1043
Casting Iron - C.W. Ammen, TAB Book 1610
Some visitors to this website may have read about my foundry in John Robison's book. It was a fully equipped one. When I went away to Graduate School, I could not take this foundry with me. My crucible furnace weighed about 800 pounds. The other equipment, as well as a ton and a half of molding sand, were not very portable either. I had to sell it all.
But I eventually missed the joy of pouring molten metal, so I designed and built a workshop scale furnace that was very portable. A hobbyist might want to build something similar, so here are some details.
DISCLAIMER: It is assumed that you know what you are doing. I cannot assume any responsibility if you hurt yourself building or using any of the tools hereinafter described.
This design uses stackable cylinders to implement a furnace of adjustable capacity. You will need to get or make crucibles of different heights in order to take advantage of the adjustability. It can be gas fired or electrically heated. It easily handles aluminum. It will probably handle bronze. It is unlikely that it could handle cast iron.
 Fig.1 - Fully Stacked Furnace |  Fig.2 - Base Pieces |
The cylinders are two inches thick and packed with refractory cement that is cured by drying them and then running the furnace. The outer rings of these cylinders are here welded up out of 1/8" by 2" steel strap. Protuberances must be welded to the inside of the rings in order to keep the rings and refractory as one piece. I seem to recall doing this by arc-welding the tip of a 1/8" welding rod to the ring and then quickly removing the electrode clamp and holding the rod in place with the other hand until solidified (using heavy non-conducting gloves of course). The rod is then snipped down with bolt cutters. A dozen of these per ring ought to do the trick.
A screwed together plywood form can be used to hold the steel rings and form the central hole while you pack the refractory cement into them. The form should include a larger diameter piece to form a ledge for the electrical heating coils (from a kiln supply) to sit in. Quarter inch plumbing pipes can be cast in place for the bolts to pass through that will be the power terminals. The refractory will act as an insulator. Make sure that the holes in the steel ring for these to pass through are large enough to prevent a short circuit.
The base and the lid can be packed with the form center pieces unscrewed. A copper pipe can then be used to cut a center hole in the lid refractory for venting. One of the rings can be made into a torch ring (see figure 4) that can be stacked on top of the base so the furnace can be gas-fired (I haven't used this yet).
 Fig.3 - One Ring with Heating coil |  Fig.4 - Torch Ring Alternative |
Big ring-clamps can be fashioned to securely hold the stacked rings in place and control heat leakage between them. The two shown in figure 5 were made from the kind of steel strap that is used to tie down mobile homes. You may want to use a thicker gauge of steel strap.
The heating coils can be wired in any combination of series and parallel that you see fit. You need only rig them to get the desired wattage in accordance with basic electrical formulae. You will doubtless need 220 volts to run such a furnace. You can use 30-amp circuit breakers for switches. You should ground the furnace.
The crucible you see here was made from a piece of 6" diameter steel pipe with 1/4" wall thickness. A disk is welded to the bottom. In use, this crucible oxidizes and flakes, but this is tolerable for hobby aluminum casting. A silicon carbide crucible from a foundry supply might be better, but some capacity will be lost to the greater wall thickness.
 Fig.5 - Medium Furnace with Crucible |  Fig.6 - Tongs, Crucible, Hinged Pouring Shank and Ladle |
You will need crucible handling equipment. Three pieces I welded up are shown in figures 6 and 7 - tongs, hinged pouring shank and ladle. The ladle was made from a plumber's lead pot with a rod welded to the inside bottom of the pot. This can be inserted into the crucible while it is still in the furnace. This is great for continuous melts such as when making ingots from scrap or casting many small pieces. Warning! Don't design your pouring shank to closely fit your crucible while it is cold. The crucible becomes very significantly larger in diameter when it is hot. Allow for this.
Wear a full face shield and molten-metal resistant clothing.
Running the furnace electrically is very quiet. It should not annoy the neighbors unless they are technophobes with mechanical superstitions.
 Fig.7 - Another View of the Tools |
Happy casting!