DIY

Build Your Own Home Metal Foundry

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With a few simple tools, you can set up a home metal foundry.
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The blueprint of the furnace used for founding.
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Be careful when pouring metal castings.
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The blueprint of a metal founding flask.

It’s funny how an event will sort of get stuck
in your mind. I can clearly remember, some 20 years ago,
holding a complicated-looking — and
expensive — machine part in my hand and thinking how
difficult it must be to form that piece. Today, however,
I’m able not only to duplicate that part (for pennies), but
am able to make just about any component I need — to equip my
shop, fix my car or merely tickle my fancy — by going
no farther than my own back yard! Did I buy a tool-and-die company? Well, not quite. Instead, you might say I “founded” one, for a total
investment of about $30 and the time it took me to learn,
through experience, the basics of home metal casting. 

Establishing a Compact Foundry 

Believe it or not, it’s fairly easy to establish a compact
foundry at home, since — if you enjoy puttering around
the house — you probably already have on hand most of
what you need to build one. Metal casting (a craft
that’s been practiced for thousands of years by so-called
“primitive” people) harbors no secrets: If you can whittle
a whistle, you can make a pattern … if you’ve ever built
sand castles, you can make a mold … and if you can boil
water, you can melt metal and pour it into that mold. It
really is that simple.

Of course, I never intended to take up foundry work just
for fun. Someone (whose name is long forgotten but whose
message has hung on) once told me that a metal lathe is the
only machine in a shop that can duplicate itself. So,
thinking about the old chicken soup recipe that starts out
“first you get a chicken,” I figured that if I could build
a lathe — using my new casting skills — nothing
would prevent me from going hog-wild and manufacturing all
the other tools I needed to outfit my workshop.

However, I hadn’t counted on the unsolicited
business that came my way once I’d set up my home
foundry (and has often kept me too happily busy to cast
tools for myself). When word got around that I was casting
metal, it seemed the whole dang county was beating a path
to my door, looking for me to make kitchen utensils, repair tool parts or fabricate structural members (for
wind plants, greenhouses, geodesic domes and more) in
exchange for goods, services or cold cash. After a
while I began casting distinctive objects of art
that — with the help of a simple on-site foundry
demonstration — paved my way with green at local flea markets
and crafts festivals where enthusiastic onlookers fairly
tripped over themselves to better their view and
lighten their billfolds!

The Basic Components of a Metal Foundry

When I said it doesn’t take much material to set up a small
foundry, I meant it. For example, wood charcoal
is the “classic” foundry
fuel although the casting industry now uses natural gas
almost exclusively. But after an unsuccessful attempt at
using a homemade gas burner, I switched to charcoal
briquets and have stuck with them ever since.

Besides being inexpensive and readily available, the solid
fuel can fire a foundry that’s set up in a rural area where there might not be a gas line. Better yet, the
charcoal can even be manufactured right on the homestead
(simply cover ricks of hardwood with earth and allow them
to smolder from within for several weeks). Doing it
yourself has an advantage other than low cost, too, because
homemade charcoal doesn’t contain the binding
agents — found in store-bought briquets — that
eventually create airflow-blocking klinkers in the furnace.
(The charcoal-making process also yields gaseous and liquid
by-products — such as methane, wood alcohol and other
volatiles — that can have value in themselves.)

Naturally, to use the fuel efficiently, I needed a suitable
oven. So, I built just such a furnace, out of scrap, for
about $20. It’s nothing more than a drum, with a removable
lid, that’s lined all around with about two inches of
castable refractory, has an air-feed tube built into its
bottom and is equipped with an adjustable-for-flow
blower to supply the draft necessary to create intense
heat.

Before constructing my furnace, I first determined how
large it would have to be to handle the parts I planned to
make. I’d suggest that a beginner locate a vessel at least
the size of a 50-pound refrigerant container, then try to
salvage a 30-pound canister from the same source.

Perhaps better yet, if you can find a 30-gallon drum and a
5-gallon paint pail, you can build a furnace that will be
tall enough to accommodate most pieces of melting scrap, no
matter how oddly they may be shaped. (When doing aluminum
casting, which, because of the low temperatures involved,
is the least difficult — and safest — foundry
craft, I melt down discarded auto pistons almost
exclusively. Most garages will let me have them free for
the taking, and they’re made of high-quality alloy. Many of
them do, however, come with connecting rods attached, and
these — along with any other ferrous parts — must be
fished out of the melting pot before the aluminum is
poured.)

When you’ve selected a suitable furnace vessel, prepare it
by first slicing off its lid — near the uppermost
seam — then cutting a hole in its side, close to the
bottom, large enough to accept a 16-inch section of 1-1/2-inch feed
pipe. Thread a 90-degree elbow to the inside end of this
nipple, then weld the assembly to the canister wall, with
the elbow pointing upward. Next, cut a hole in the middle
of the lid section, and weld a short length of 2-inch
muffler tubing in place, allowing it to protrude below the
lid’s lip slightly. Then fasten some handles — made
from short pieces of 1/8-by-3/4-inch flat stock and 6 inch pieces
of 1/2-inch pipe — to the sides of the container.

Because of the extreme temperatures generated within the
furnace, its floor, lid and inner walls must be
lined with refractory material. Paco
Cast is a good castable refractory product.
Simply mix up the necessary quantity, following the
instructions on the bag, then fill the bottom of your
furnace container until the material reaches the top of the
air-feed elbow (it’ll usually do so at a depth of 1-1/2 to
2 inches).

Next, coat the outer skin of the smaller of your two
vessels with oil (to allow for its easy removal after the
wall lining has set) and place it upright on top of the
elbow and the “pasty” base pour, making sure that it’s
centered evenly within the furnace drum. Then go on to fill
the wall cavity with refractory as you did the bottom, but
tamp it down as you pour to discourage the formation of air
bubbles. Finish the job by inverting the lid and lining it,
to the level of the muffler pipe, in a similar manner.
(Hint: Weld some short steel bar loops to the inside of the
cap to give the mix something to grip as it sets.) When the
refractory is dry, remove the inner vessel and “cure” the
furnace by burning charcoal in it — closed — for at
least 12 hours.

With this done, cut a piece of 1/8-inch expanded metal into a
disk just large enough to slip inside the furnace, then
attach a blower (my “squirrel cage” puts out about 100
cubic feet per minute and uses a sliding flap damper to
regulate flow — although an old hair dryer with a
rheostat control would probably work just about as well) to
the feed pipe . . . using a coupling, a welded plate or
even a piece of bicycle inner tube if that’s what it takes
to make the hookup.

You can probably construct the second most important
foundry component — the flask — yourself, too. It’s
really nothing more than a two-part open-ended box that
holds the sand that forms the mold. The size of your flask
(its top section is called the cope, and its
bottom the drag) will, of course, depend on the
size of the castings you hope to pour and you can fit a
simple four-sided cheek between the components to
increase the flask’s depth if necessary. However, I’ll tell
you how to put together a beginner’s box that will do for
almost any job you’ll care to tackle for a while.

First, find yourself some clear, straight 1-by-4 and cut
eight sections from it: four about 10 inches in length and four
more 12 inches long. Then trim off eight 2-inch slices and make the
pair of boxes, using glue and No. 6 by
1-1/4-inch wood screws to hold the boards together. (If you
decide to build a larger flask, cut a 1/4-by-1/2-inch rabbet
into the inner face of both the cope and the drag, all
around, to give the sand something to hold on to.)

Now make two sets
of keys for
the sides of the flask. It’s important that the cope and
drag fit consistently flush, so the mold will separate
cleanly at the parting line. (Some folks prefer using dowel
pins or rods instead of tapered keys, since they leave less
room for error when lifting.) Finally, seal all the wood
with a good waterproofing agent.

You’ll also need to fashion a riddle and a
molding bench, but both are easy to make. The
first is merely a sand filter, built by nailing together a
16-by-16-inch frame made from 2-by-4 and tacking some 1/4-inch
hardware cloth across it (1/8-inch grid material can be used
for fine detail castings). The molding bench is a 2-by-4
wooden frame about 36 inches square, with a 1/2-inch plywood bottom.
Finally, make at least two pattern boards, by
cutting plywood sheets slightly larger than your flask and
coating them with wood sealer.

Most of the remaining tools and supplies can be found in
your own kitchen, workshop or — if you want to get
fancy — at an arts and crafts supply store. You’ll need…

  • A wooden hammer handle about 10 inches long for a rammer
  • A piece of 1/2-inch conduit or tapered dowel, 6 inches in length, to
    serve as a sprue pin (don’t worry about these
    terms — you’ll understand what the tools do
    later)
  • Another smooth dowel, 1/2-by-6 inches, for a riser
    pin
  • An assortment of small spoons and knife blades a sprinkling can (I use a plastic milk jug with holes
    drilled in its lid)
  • An iron rod with a hook bent into
    one end and a handle into the other
  • A 6″ cast-iron bean
    pot to serve as a crucible
  • A pair of
    scissors-type tongs at least 24 inches long (make them from 1/2-inch
    rod, pivoting — at a point closer to the jaws than to
    the handles — on a 1/4-inch bolt, and with a curved steel
    band on each jaw that fits the side of the crucible
    perfectly)
  • A wooden straightedge
  • A camel’s-hair
    artist’s brush
  • A tin (not aluminum) muffin pan
  • An
    assortment of iron pots and pans of various sizes
  • A small rectangular tin bread pan
  • A rapper
    (just a large washer with a steel handle welded to it —
    or a tuning fork)
  • A skimmer, which is like a spoon, but with a two-foot rod handle

You will, of course, also need some casting sand, which you might as well pick up at a local commercial
foundry, since it’s hard to locate appropriate indigenous
material. I find olivine sand (it’s brown in color and
contains about 5 percent bentonite as a bonding agent) to be the
best choice, though black Albany sand also works pretty
well. You’ll want to locate some pumice dust, too, to serve
as parting powder (don’t try to substitute talcum
because it tends to absorb moisture).

Make a Metal Mold

You’re now ready to make a simple mold. First, sift the
dust from your briquets, place them in the bottom of the
furnace over the screen, ignite them and turn the blower
on. Then prepare the crucible by filling it with aluminum
scrap (be extra careful — especially when melting
pistons — that there’s no water trapped in the
parts to be melted).

With the coals hot, place the crucible in the furnace and
install the lid. While you’re waiting for the alloy to
melt, prepare about five gallons of sand, in your molding
bench, by sprinkling water into it a bit at a time and
tossing it with two wooden blocks to bring it to a
dry-paste consistency (5 percent to 7 percent moisture) which
allows it to remain whole when squeezed, but to break
cleanly when released (you’ll probably have to put in some
practice before you’ll be able to recognize this stage).
Better yet, mix the sand about 12 hours prior to casting,
so that its wicking effect will have time to distribute the
moisture evenly.

Next, place a pattern (it can be a component you want to
duplicate, or a piece of wood or polystyrene foam you’ve
whittled to a specific shape) on your pattern board, within
the molding bench, and dust it lightly by shaking the
pumice through a sock. Place the drag upsidedown
over the pattern and — using the riddle — sift your
sand into the drag. Pack the grains firmly around the
pattern with your fingers.

When it’s covered, pour coarse sand on top till the drag
box is overfilled. With the rammer, tamp the sand tightly
at the corners but somewhat less firmly over the pattern.
Use one of the pattern boards to compress the sand into the
drag with a downward and right-and-left twisting motion.
Strike off the excess material above the edge of the drag
with your straightedge, then vent the mold by piercing the
sand — using a short length of pointed coat-hanger
wire — in several places above and down to the pattern.
Scrape all the fallen sand away from the drag with your
bread pan.

At this point, check your crucible to see whether the
aluminum is melted. If it’s bright red, it’s too hot and you should reduce the air-feed flow so the molten metal
can just simmer while you complete the mold.

Now, go back and flip the drag right side up, redust its
face (with the pattern still inside) and place the cope on
the drag. Put the riser pin (it’s used to compensate for
shrinkage during a pour) on the thickest part of the
pattern, set the sprue pin into the drag sand at a
point an inch or two from the pattern, hold the riddle
over the cope and repeat the sifting, tamping and
striking procedures as before.

With this done, dig a small pour basin, about an
inch deep and an inch from the sprue pin, with a spoon and cut a channel, half as deep, from the pit right to the
sprue pin. Vent over the pattern again, then carefully
remove the riser and sprue pins, finger-press the sand
around the basin (taking care not to let any material fall
into the riser — that is, the hole left by the riser pin)
and separate the cope from
the drag.

Take your spoon again and dig a runner in the drag
sand from the sprue, alongside the pattern, ending in a
gate (which is a connecting ditch leading directly
to the pattern) and press the sand down as before.
(Actually, in some cases, more than one runner and gate
might be used.) Now, swab a thin film of water around the
edge of the pattern with your brush, and prepare to remove
the original by first threading a small wood screw into
some convenient part of it, then tapping the screw back and
forth and all around with the rapper till the pattern
loosens and lifts easily. Repair the mold if it’s damaged
in any way, blow any sand from the area of the impression,
and carefully replace the cope, double-checking its fit.
You’re now ready to make a pour, but first cover the
exposed wood of the molding bench, around the flask, with
sand. 

Pour a Metal Casting

Open your furnace and remove any ferrous parts from the
crucible with your hook, then skim the slag from the molten
aluminum’s surface (disturbing the melt as little as
possible) and throw it in a waiting iron receptacle. Lift
the crucible from the oven with the hook, set it down in an
iron frying pan and grab it firmly with the
tongs. Pour the molten alloy into the basin and sprue till
it comes out of the riser, then dump any unused fluid
aluminum into your muffin pan, to form ingots that you can
remelt later.

While waiting to part your mold (it’ll take 20 to 30
minutes for the casting to cool), you can resift the
surplus sand and store it in a sealable container for next
time (do the same with the sand in the mold after the
casting is complete) and smother your furnace fire (save
the cooled leftover coals … they’ll make your next fire
especially easy to start).

Once the time is up, shake out your casting and look it
over. Don’t be disappointed if the first efforts are a
little rough. With practice, you’ll be able to knock out
work that’s consistently suitable for tapping, turning,
milling or any other kind of machining.

Safety First When Working With Metal 

This is important, so I’m not going to mince words:
Always wear leather gloves and boots and
eye protection when working with the foundry.
Never pour water on molten metal … always use
sand to prevent, or put out a pouring-related smolder or
fire. Work in a well-ventilated area or outdoors and avoid
breathing both the charcoal and the aluminum fumes because
they are toxic. Don’t make a pour over bare wood
or concrete, and never set your furnace down on a wooden
floor … raise it up on firebrick or refractory. And
remember: Keep water — in any amount — out
of your crucible!

Learn as You Go

You won’t likely manage a perfect pour the first time. In
fact, you might have to make quite a few castings before
you get each step down pat. I can’t help you practice, but
I can recommend that you read as much about small-scale
founding as possible and after a while you’ll become
proficient at what is probably one of the greatest
self-sufficiency skills of all!