Introduction: Benchtop Foundry and Forge
Backyard metal casting opens up new avenues of adventure, skill, and creativity at a modest cost of investment. The learning curve is not steep, and thanks to the internet, plenty of reliable information is available to launch a humble yet productive little endeavor. This build has served me well and was put together entirely with salvaged parts, as are so many forges and foundry furnaces, and in that respect it plows no new ground, but I think it positions well for some of the novel features it has as will be explained below.
Step 1: Safety First
Fire and molten metal are dangerous! Ensure you have educated yourself on the ways and means of personal protection before attempting any experimentation of this craft.
Step 2: Inspiration Strikes!
I was straightening up around the shop when by happenstance I placed an upturned cutoff of a propane tank top on a coffee can. I instantly realized I was looking at 90% of a typical forge construction. Doing a dry layup of the rest of the system, I opted to build the forge's supporting structure using metal- clad plywood, and proceeded to use scrap wood and metal pieces on hand.
Using a Dremel tool, I first cut the blowpipe hole into the coffee can after marking the location with a paper template. Using a round stone next, I finished the hole for a slip fitting of some 2-3/8” [61mm] diameter metal fence post to supply combustion air.
Step 3: Air Supply
I wired up a pulse width modulator speed control to a 12 volt d.c. brushless centrifugal fan motor salvaged from a projection television. This gave a good, controllable firing range, and I also made a transition nozzle to go from round pipe to square fan outlet. Finally, I housed it all in a simple box, and mounted it to the metal clad base.
The coffee can plenum is simply secured with a central screw- the pipe clamp shown was not needed after assembly.
In practice, the air undergoes some preheat in the plenum which enhances combustion above, and being under a positive pressure keeps the can relatively free of ash.
Step 4: Final Assembly
The air inlet nozzle, or Tuyere, is made by simply boring holes in the base of the bowl- the former tank top. I also used the tank shutoff valve as a bottom plug after cutting it free and drilling more air holes in it. A metal clad upper deck adds considerably to the usefulness by acting as a trivet for the crucible and also as a hot tool rest.
Step 5: Fuel
In the subdivision where I live, people seem to frequently discard furniture, lumber, cabinetry, etc. Just about all kinds of free fuel which feeds my fire, I've yet to spend a penny on fuel and it doesn't look like that is about to change anytime soon. Wood suffices for what I do and I simply cut it all up into biscuit- sized pieces and feed in as needed. Charcoal, propane, and waste oil are other popular fuel alternatives, each having it's own pluses and minuses too.
Step 6: Aluminum for Melting
Likewise, a weekly “Asset Recovery Sweep” of my neighborhood provides me with plenty of raw material, that is to say scrap aluminum, in the form of motors, pumps, lawnmowers, weed whackers- just about anything which is preferably made of cast aluminum. The only source I avoid is beverage cans, they are not worth processing due to very low yield of clarified metal.
Step 7: Good News/ Bad News
Initially I enjoyed great results, my objective is clarification of the scrap and recasting as ingots, ready for a serious project. Muffin tins from the thrift store work well for this, and with a little imagination other shapes can be simply cast, such as round rod. I stuck some tube cutoffs into a can of supporting sand and poured off into them, fetching some really useful rod with no dross or pinholes in them. At about $6 a length, that is some real savings for future projects.
Step 8: The Bad News
The first image shows what happens when you unmold too quickly. The muffins lost their form and crystallized into broken up shapes. I should have waited at least 15- 20 minutes, but my timing was screwed up and so... They will be melted again however, so it is no loss.
The real potential for serious damage happens during a crucible failure, and my $3 thrift store sauce pan had one. I have to say though, that after 8 or 10 melts, it owed me nothing and I ended up with about 15 pounds of clarified ingots before it expired. It took the form of seepage through two pin holes (red circle) and dripped into the plenum, through the Tuyere holes. After cool down, the blockage was cleared and even the blob at the plenum bottom was sent to the clarified pile, so no real loss of any consequence was had. The ash you see by the way, is typical after a session, not much at all and a short puff of air cleans it all out, so that points to a very efficient design.
Step 9: The Process
A forge can tell you certain things if you just listen closely; a change in pitch of the sound can mean more fuel is needed, or an unseen air blockage is happening, preventing complete combustion. Then too, the firing rate can be adjusted to efficiently do the required task without being wasteful of fuel. Some operators like the sound it makes when pumping it up with a huge volume of air; it kind of sounds like a Saturn 5 rocket lifting off, but of course that creates an exponential consumption of fuel with not much more benefit to the melt. So, depending on the firing rate, I occasionally lift the crucible, letting the upper wood chips slide down into the Tuyere area to further fuel the melt as my senses tell me.
Step 10: What's Next?
I have, waiting in the wings, a more “industrial” designed foundry using the legendary propane tank, however, the benchtop design meets or exceeds all of my current needs, is easily set up and taken down, was an inexpensive build and is fuel frugal, so this unit sits up on the shelf, awaiting a calling that may never come.