Start by positioning the furnace base securely in an area where there are no flammable materials nearby. Attach the alligator clips from the power cord to their corresponding terminals. Next, load the crucible with aluminum pieces before setting it atop the heating element. Insert the thermocouple probe near the crucible's top and securely place the lid over the furnace. Connect the power cord to an outlet, then closely observe both the power and temperature as the aluminum undergoes melting.

Even though power meters for 240 VAC setups can be pricey, testing power at 120 VAC suffices. This is because power is proportional to the square of the voltage, thus 240 VAC translates to four times the power compared to 120 VAC. I recorded a wattage of around 350 to 360 Watts at 120 VAC, indicating that at 240 VAC, I would receive approximately 1400 to 1440 Watts. Also, power is expressed as the product of voltage and current, leading to currents of about 3 Amps at 120 VAC and around 6 Amps at 240 VAC—these figures reflect the typical measures for most elements rated 6.

Aluminum has a melting point of approximately 660 degrees Celsius, but it ideally needs to reach about 700 to 750 degrees Celsius for effective pouring without premature solidifying. Remember that the temperature displayed by your digital thermometer will initially reflect the air temperature over the crucible, which heats faster than aluminum itself. If you're working with a 120 VAC system, allow the temperature to reach around 730 to 750 degrees Celsius before pouring.

For those operating at 240 VAC, the air inside the furnace heats up significantly quicker than the aluminum, leading to thermometer readings that could misrepresent the actual aluminum temperature. In such cases, I recommend maintaining a 'soak' period, where you hold the temperature between 700 and 750 degrees Celsius for about 5 to 10 minutes. Ideally, wait for the thermometer to peak at 750 degrees Celsius before disconnecting the power cord. When the temperature drops to around 700 degrees Celsius, reconnect the power. This cycle should be repeated for another 5 to 10 minutes before proceeding with the pour.

If your casting activity is extensive, investing in a temperature controller might be worthwhile, but for casual hobbyists, manually managing the temperature by monitoring thermocouple readings and controlling the power cord should suffice.

Casting Furnaces

Your furnace's size and temperature capabilities should align with your specific needs. My work predominantly involves aluminum, which melts at about 1220°F. My compact Flower Pot Furnace can have aluminum ready for pouring within approximately 20 minutes, while my larger 15-pound furnace may take several hours to prepare. Additionally, I required a furnace that could achieve higher temperatures to accommodate brass and iron casting, so carefully consider your project requirements while selecting your furnace. All three furnace designs are outlined further below.

Brass and Iron Furnace - 2200°F

For higher temperature metals such as NiBrAl at 2100°F and iron at 2800°F, a clay or silicon carbide crucible must be used. Consequently, your foundry construction should prioritize the crucible’s dimensions. An A30 crucible is roughly 8 5/8" in diameter and 11 1/2" tall, capable of holding 66 pounds of brass or 21 pounds of aluminum. Alternatively, the larger #35 crucibles sourced from Legend (www.lmine.com) measuring 9 1/2" in diameter and 12.5" tall ensure ample metal supply for casting applications, including propeller blades and other components found in marine settings.

My partner Kay and I consulted with Jeff Trenholm at our local Canfield & Joseph foundry supply, who provided valuable insights regarding furnace and investment supplies. We returned home with $400 worth of materials for constructing a furnace light enough to be portable for boat trips. The key to lightweight constructions was incorporating ceramic cloth and insulating firebrick or IFB. Jeff supplied us with blueprints for a more extensive crucible furnace as well; my initial concept was inspired by designs from metal casting forums that suggested 1” of castable refractory as the hot face with 2” of ceramic cloth behind it. Jeff's professional guidance recommended walls of at least 6 inches, with a minimum of 4 inches of castable refractory. After explaining the importance of a lightweight design, the thermal calculations demonstrated that IFB with a couple of inches of ceramic fiber insulation would suffice. The lid was exclusively constructed from ceramic fiber, ensuring the exterior surface remained at a manageable 500 degrees Fahrenheit. However, it is essential to note that this structure is not ideal for frequent iron casting at 2800°F, although it's perfectly satisfactory for melting brass and NiBrAl at 2100°F.

A 55-gallon oil drum serves as the outer casing, allowing space for firebrick and ceramic fiber insulation even with a 9.5” diameter crucible, yielding around 5” for insulating material and added room for tools to reach the crucible.

A Material List includes:
2 - 55 gallon Oil Drums
1 - 55 lb bag of MetalKast 70 castable refractory.
1 - 55 lb bucket of Sairset refractory mortar (only need 1/2)
1 box of Ceramic Fiber Blanket - Cerablanket, 2 x 150 x 24", 25 sqft, 8 lb/cuft
40 - F Insulated Firebricks, measuring: 2.5 x 4.5 x 9"
4 - TIG welding stainless steel filler rods or 12 ft of 1/8" diameter stainless steel wire.

Sairset should be stored in a cool, dry location with a shelf life of 12 months. Make sure it is tightly sealed if you plan to store leftovers, and mix thoroughly for optimal results. Thin brick joints yield the best outcomes as each joint needs to be entirely filled with mortar.

Cut and prepare the oil drum to about 21", depending on the firebrick size. We utilized a masonry saw for the firebricks but a hand saw will suffice as well. Remember, don’t inhale the dust!
Prepare Insulating Fire Bricks, or IFB, cutting them to fit the oil drum’s base.
Cover up the bung holes, apply some Sairset, and compact the bricks into place.
Lay IFB with minimal joints, working quickly since it dries rapidly.
Cerablanket Ceramic Fiber Insulation can easily be cut with a serrated blade, fitting snugly against the drum's inner lining.
Set the Cerablanket firmly in place.
With one side of the firebrick propped up, you can easily shape them into wedges to form the furnace walls. Despite strong winds, using a respirator during this task is advisable.
Utilize two 12" round boards as jigs, trimming the last brick once the others are settled since the mortar adds about 3/4".
The lid will be fashioned from 4 inches of the barrel base, as that section lacks bungs. A 5" hole should be cut into the metal, incorporating 4 inches of Cerablanket within and a sheet metal ring welded around it to secure the Cerablanket.
Remove 4" from the bottom of a second 55-gallon oil drum, which will be welded as the furnace bottom after placing 4 inches of Cerablanket inside.

Stainless steel TIG welding filler rods are welded at the lid's base and bent to overlap the Cerablanket surrounding the furnace vent.
Metal flashing is then utilized for casting the Metalcast-70 castable refractory, which protects the Cerablanket from damage while adding materials and safeguarding the stainless wires.
Finally, apply castable refractory around the exposed Cerablanket at the furnace peak.
The remainder of the castable refractory seals around the burner hole and creates various supports called plinths to hold the crucibles in place.
Trim the fire bricks to align with the refractory edge.

Initial Melting

The day you first utilize your newly constructed furnace for real tasks is truly exhilarating, especially if it involves parts worth saving you $3,400—making it an investment that pays for the furnace and a new metal lathe.

For this procedure, we chose a clay graphite crucible from Legend.

Foundry Equipment

The background displays crucible lifting tongs used for extracting the crucible from the furnace and positioning it onto a plinth to facilitate pouring, which requires two individuals using the pouring shank visible in the foreground. The square tube attached to the pouring shank fits onto the crucible's top lip, preventing accidental exit while tilting.
Also included are tongs for adding metal to the crucible, a fluxing tool (essentially an end cap on a metal stick used to push flux down), a skimmer for removing dross that accumulates atop the melt, and a plate used to push leftover dross or flux away from the crucible's edge during metal pouring.

To achieve temperatures of up to 2800 degrees, simply relying on a propane burner won't suffice. Fortunately, Super Dave (not his real name), who lives just 100 miles away in Oklahoma City, has engineered an excellent forced-air propane and waste oil burner. He comes from a background in asphalt plants, so he knows his burners—finally persuading him to construct a replica for me. :)
The burner pipe must possess an inner diameter of at least 2 inches, although a larger size will work as well. Its length should be around 16 inches but can be adjusted as needed. The burner can function without the tabulator, or you may opt to fabricate your own from sheet metal, as it’s not complex.

For purchasing burner components, visit:
www.patriot-supply.com
Burner Components:
Siphon Type SNA Air Atomizing Nozzle, .75 gal/hr, Hago Delavan Part Number: -8 - $25
Adapter for Nozzle: Hago Delavan Part Number: -$24

Large Aluminum Furnace - 2200°F

The inception of my foundry came from extensive research on various informative websites. As referenced at the page's end.
With a goal to melt up to 15 pounds of aluminum, I sourced a crucible slightly larger than the standard #10 size. The crucible itself is forged from a 6-inch by 1/4-inch-thick steel pipe topped with a 1/2-inch steel plate on its base. Collectively gathering materials from local salvage yards and foundry suppliers while assembling the burner from parts stripped from my turkey fryer, I was fully equipped.
Two 30-gallon oil drums (costing $4 each) became the furnace body, while Mizzou Castable Refractory sourced from a nearby supplier delivered the necessary insulation.

Primarily working with aluminum thus far has pushed my cutting equipment to the limit, particularly my Dewalt cut-off saw, which often required $90 blades subject to quick wear. With sharpening costing $40, I opted for an acetylene torch before trying a cutting blade attached to my grinder, which yielded surprising results as Harbor Freight offers a box of 25-7 inch metal cutting discs for merely $14, plus I acquired an affordable angle grinder for $20-30.

(1) One of the 30-gallon barrels was trimmed to 18 inches, forming the furnace base. An angle iron frame established four legs—supporting a pipe pivot for the furnace lid—and meeting the drum's diameter of 14 inches aligns perfectly with my over 6-inch-wide crucible, providing an inch between the crucible and refractory for a thickness of about 2 1/2 inches.
(2) The lid itself is cut from 2 1/2 inches of another barrel, utilizing drums with lids like paint cans. Instead of attempting a weld for a lid, I simply repurposed another $4 barrel. Some have employed pressure storage tanks for household water systems; while their rounded shape enhances practicality, it does impose challenges for welding thin metal presented in 30-gallon barrels, which remains outside my skill set.

(1) The angle iron frame surrounds a 30-gallon drum.
(2) Pipe structure welded onto the oil drum lid utilizes rods for additional rigidity along with a container to help shape the vent.
(3) Mizzou Castable Refractory is poured in and vibrated into place using a tabletop vibrating system beneath.
(4) Mizzou is poured in about 3 inches deep into the base, and a hole drilled in center facilitates metal drainage should the crucible fail.
(5) An interior form shaped by wrapping aluminum flashing around wood furring strips glued to the steel crucible.
(6) A burner pipe is shaped to sit seamlessly along the inside form of the crucible.
(7) With the burner pipe installed, Mizzou is added and vibrated into place.
(8) Remaining Mizzou can be fashioned into plinths and even a flower pot furnace.

(9) Mizzou curing is accomplished via gradual heating over several consecutive nights.

Mizzou Castable Refractory

Refractory materials are fundamental to insulating your foundry. Although it’s possible to create your own, the scarcity of components prompted me to purchase Mizzou Castable Refractory instead. This product might resemble concrete but is distinctly different and has a 30-day shelf life, enhancing its affordability.

When I returned some unused Mizzou bags, I noticed they had a whole pallet exposed to rain, having surpassed its 30-day expiration. They would’ve gladly permitted my use of that. I learned they manufacture crematorium pans that support bodies placed in their furnaces, alongside operating a crematorium facility, as I noted large smoke stacks adjacent to the warehouse.

First, always read the instructions! Mainly composed of alumina, which is aluminum oxide, utilize proper safety gear, including a respirator and gloves. It required four 55 lb bags priced at $27 each to complete my furnace.

For each 55 lb bag, only 5 pints of water are necessary, resulting in a powdery dry mixture resembling cement. The secret lies in vibration; if you possess an old table saw, you’ll have an effective method to vibrate ceiling materials. Just lower the blade, cover it with plastic, start it, and let its vibrations settle your refractory.

(3) I first molded the lid so I could examine the mixture's behavior before proceeding with a larger cast. Essential steel bars are welded for reinforcement on the lid. These only appear on the lid to support the refractory, minimizing crack susceptibility. A butane torch, encased by cardboard, protrudes through the lid, creating vent and sight openings at the top.
(4) Pouring occurs for the base, aimed at a 3-inch thickness. A 3/4-inch PVC pipe inserted through a center hole drains any molten metal should the crucible malfunction. Channels are sculpted in the refractory to effectively channel liquid metal toward the center drain.

(5) While the base dried, I constructed a 6-inch crucible from a steel pipe with a 1/2-inch plate at the base. This crucible formed the primary mold for the refractory. Strips of wood slightly over an inch wide are glued onto the crucible with Liquid Nails, encircled in aluminum flashing. Folding the flashing over the top enhances material loading simplicity into the center form with less risk of missing the opening.

(6) (7) Once the bottom solidified, the center form and burner inlet pipe—a 2-inch steel pipe—were installed to fit snugly against the center shape. It was secured with Liquid Nails and a metal piece that pierced through the center form.

(8) With excess materials left behind, I also crafted several plinths and a flower pot furnace. The flower pot furnace is unique, composed of a couple of flower pots lined internally with Mizzou. This design is efficient for lightweight jobs, attaining temperate output in about 10 minutes.

(9) Curing entails prolonged heating processes. Mizzou contains precise heating directives for the curing of your furnace. My approach involved multiple evenings of slow heating, initiating with heat lamps, then using the burner at minimal capacity afterward. My gradually ramped sessions would attain 250 degrees Fahrenheit and higher over subsequent nights, ultimately achieving the successful melting point for aluminum after several days of meticulous heating.

Propane Burner

(10) My burner apparatus utilizes an aluminum 2-inch to 3/4-inch reducing bell, letting me create a tailored fabrication while playing on the lathe; unavailable local plumbing supplies compelled me to explore lathe capabilities. The construction consists of an 8-inch long 3/4-inch nipple accompanying a flare reduced from 1 inch to 3/4 inch. Within the flared region at 1-inch, I cut and smoothed threads on the lathe, which likely wasn’t essential. Just earlier, I reclaimed the 5 PSI regulator hose and orifice from my bargain turkey fryer, previously used for lead melting, though the regulator is optional; though it enhances gas flow, it complicates manual flame control.

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I also welded six small flat steel pieces to the 8-inch nipple to centrally align the burner within the burner pipe, maximizing airflow externally; one steel tab prevents excessive burner penetration. Maintain sufficient fuel input to ensure the flame dances only at the bell's flared end. If reduced, the flame retreats into the 3/4-inch pipe, igniting within the intake bell and overheats, posing extensive risks not excluding the propane tank.

After several tests with small melts, the setup proved flawless, melting a few pounds in 30 minutes yet slightly exceeding an hour for about 8 pounds. While grander burners expedite the process to 15 minutes, the tranquil nature of melting allows for multitasking around the shop—no need to rush, yet I optimize propane costs where possible. Smaller crucibles afford easier handling, eliminating the need for pouring funnels.

Crucible Tool

(13) This design draws inspiration from several other models encountered. It boasts two hooks designed to sink into the furnace while securing 3/4-inch parts affixed to the crucible's outer edges. The hooks are coupled to a 7-inch pipe that rotates along the tool's handle. Once the crucible exits the furnace, a rotation enables the attached arm to pivot downward, capturing the crucible's base.
(16) The crucible can then be tipped for pouring. Although images serve for exposition, safety checks such as glove usage are crucial during actual tasks. The residue on the crucible derives from the Liquid Nails utilized to affix the furring strips during the crucible's forging process.

Should I reconstruct this, I might design the lid to encompass an additional 3 inches of furnace side, enhancing weight yet considerably simplifying the crucible tool’s mechanics. By designing substantial side openings, sliding the necessary tools directly through the crucible rather than pivoting should enhance pouring efficiency. While notching may be needed to prevent sliding, eliminating excess complexity will render the task simplified and effective.

(17) After navigating around the foundry during past operations, I grew weary of tripping over the engine stand blocking my driveway. Hence, 15 minutes later, the engine stand became scrap, and its wheels were promptly affixed onto the foundry for expedited mobility—an utterly advantageous upgrade. Now, tilting it upright allows for quick storage outdoors, maintaining some measure of rain protection through the original drum lid.

Flower Pot Furnace - Aluminum F

Months ago, remnants of Mizzou Castable Refractory inspired me to make plinths and a flower pot furnace out of spare clay pots retrieved from my neighbor's yard. Yes, I borrowed them.

(1) Two flower pots, reinforced with Mizzou Castable Refractory.
(2) Upon removal of the clay, holes were drilled for burner and ventry.
(3) The same propane burner powering my larger furnace serves to heat this small contraption.

(4) A gas cylinder cap now functions as a crucible.
(5) A rod activates through holes near the crucible's upper regions, allowing upward support.
(6) Controlling the tilt on the handle enables pouring operations.

In terms of efficiency, the flower pot furnace can melt a couple of pounds in merely 15 minutes, contrasting the larger foundry which requires almost 2 hours for a similar amount. Nevertheless, the larger furnace can take up to 15 pounds at once, though a rapid melt is facilitated using the smaller device. Ultimately, quick melts not only conserve propane but ease the handling of small crucibles.

Utilizing Flux and Degassing

For casting brass, N400, while for aluminum, N600 (PDF available).

Helpful Links

For further resources, visit:
Legend - #35 Budget Graphite Crucible priced at $60 (http://www.lmine.com)
Stanford Manufacturing - "How Everyday Things Are Made" (Covers Casting)
Back Yard Metal Casting (www.backyardmetalcasting.com)
Brian's Metal Casting Project (http://metalcast.boorman.us)—offers well-documented plans.
For Budget Casting Supply, access (www.budgetcastingsupply.com).
Lost Foam How-To: www.buildyouridea.com/foundry/lost_foam_howto/lost_foam_howto.html
Dan's Workshop: Hot Wire Lathe and Foundry (www.dansworkshop.com)

Supplier Contacts:
Gypsum Solutions – Local Distributor: Independent Materials, 34 N Owasso Ave, Tulsa, OK - 918-582-####—for Casting and Molding Plaster (Plaster of Paris) costing $20/100 lbs.
Ryder Brick - S Memorial Dr, PO Box 550, Bixby, OK–918-366-####—Firebrick (9x4.5x2) at $1.10 each.
Canfield & Joseph Inc - E 42nd Tulsa, OK - 918-663-####—offers Petrobond Pre-Mix at $0.60/lb (50lb box). Warehoused in Kansas City, 100 lbs of Petrobond pre-mixed costs $60, with additional shipping/taxes summing to $99.75 (Quotes for May).
Bryant Industrial - S 65th West Ave, Tulsa, OK - 918-446-####—Mazzo Refractory Mix 55# for $26.95.
For Polystyrene Foam (4' x 8' x 40" Bun), visit: www.creativepackagingok.com, priced at $179.20
Budget Casting Supply can be found at: http://budgetcastingsupply.com, where a 100lb box of Petrobond Pre-Mix is available for $124 (Price for May).

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