The basic parts for the furnace. A 3.5 gallon drum and a big flowerpot. Note the black ring on the drum, that's where the blower hole will go. It goes on right through the lower edge of the flowerpot.
Enhanced Portland cement (no sand used) was mixed with water until quite slushy then put in the drum.
The hole in the side was sealed with Duck tape.
The hole in the bottom of the flowerpot was bunged to stop the cement squidging up through it.
The pot was pressed in and the whole thing weighted down, otherwise the pot rises up.
Let it go off a little and then dig out the hole in the side (before it gets too hard).
A hole has now been gently tapped through the flowerpot.
I made a thick metal plate with lots of holes in it that sat on that rim at the bottom and above the air hole.
Let the whole thing dry for a week and fire it up without a blower to dry it out.
now connect a hair dryer ,blower ,fan to the whole with some pipe
add in some charcoal or make a propane torch
Lost Foam Casting
This is a method that came to me from Master Ken, my casting mentor. (1) I needed a small box that I could make into a waterproof switch enclosure, so I cut and glued some foam together then packed it into a flask of Petro-Bond sand. Regular sand would work too but Petro-Bond better fills in around the part and produces a much smoother surface and is much more likely to hold its shape. Used and burned Petro-Bond works too. There is no waiting on mud to dry, no need to dissolve the foam with acetone, and no vents are needed because the gas will pass into the sand. The resulting surface is rougher that using mud, but still good and very fast.
(2) I got to wondering if the higher density insulation foam; the pink stuff, would work? As it turn out, I was back to wanting to test some aluminum chain sprockets for a fairly low tork job. I used the one steel sprocket I had for a pattern and cut some copies out of 1 inch thick foam board. I hot glued a few of pieces together packed them into a flask of Petro-Bond, adding a 1/2 in diameter sprue through which to pour the aluminum.
(1) Cast switch box.
(2) Foam sprockets cut using a
real sprocket as a guide.
(3) Large foam sprocket part
again using a real sprocket as
(4) Spur added to the foam part
and then it is buried in
(5) Aluminum is the poured in
and that burns out the foam.
(6) The part is allowed to cool
for several minutes and the lifted
out of the sand.
(7) Completed test parts. When poured it burst into flames as expected but much to my surprise there was no violent build up of gas pressure and no spitting the aluminum back out the sprue. Without a hard plaster or mud shell the pressure was obviously defusing into the sand.
The results were fantastic! This is the kind of reliable fast part production I had been looking for. Once I had the bar stock, it is just a matter of slicing off the individual sprockets.
Obvious next step was to see if it would work with the large sprocket. If I were really talented I could cast the part by just using the Petro-Bond, but as it were I could never remove the part from the sand without messing up several of the teeth. This way I just made a foam sprocket, packed it into the sand and left it there.
I first rigged a tall fence to my hot wire cutter which is really my table saw with some minor conversions. You can see my hot wire cutter here: Hot Wire Cutter. With this I can slice a 10 inch wide sheet of foam so that it is 1/4 inch thick.
(3) I then use a few dabs of hot glue to secure my steel sprocket to the piece of foam I carefully used it as a pattern for cutting the foam is the hot wire. It is important to keep the wire as cool and possible and not to pause while making a cut against the pattern. This keeps the cutting line as thin and smooth as possible.
(4) Once the foam is cut out, it is freed from the steel pattern and a 1 inch spur is glued on. A layer of Petro-Bond is then placed in the bottom of a flask and the steel sprocket is hammer down into the sand to ensure that sand is level. Baking Soda dusted onto the steel will ensure that the sand does not stick to it. Once the sand is ready the steel sprocket is removed and the foam sprocket takes its place. More Petro-Bond fills the flask but only 1/2 of a flask is used, so it is only 3 1/2 inches high. And any sturdy heat resistant container would work. There is no need to use a flask.
(5) Using the flower pot furnace to melt the aluminum I was able to cast five sprockets in an afternoon, and four of them were good. One failed to completely form likely because the aluminum was not hot enough. I used both fresh Petro-Bond and the old burned stuff. Both worked equally well.
(6) When using Petro-Bond, I separate the burned sand out an keep in a separate bucket. Before using it again it only needs to be riddled to break up the clumps. A riddle is nothing more than a piece of metal window screen or a sifter from the kitchen. Burned Petro-Bond is fine for this type of casting since it does not have to maintain its shape, while a part is removed.
(7) I turned out not using the completed parts, but it was sure nice to have them for testing after just one evenings work