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Detailed Plans Now Available!

Build your own melting furnace! Melt and pour aluminum! Due to an overwhelming response to my improved foundry furnace, I have made available DETAILED PLANS that you can purchase and instantly download for a small fee.

You get 52 pages of instructions, CAD drawings, photos, time-saving parts checklist, suppliers list, step-by-step construction notes, and all the FAQ's, in printer-friendly pdf format!

The Original Lil' Bertha

This is a homebuilt electric melting furnace. For my 25th birthday, my wife got me Dave Gingery's book "Lil Bertha, a Compact Electric Resistance Shop Furnace." So I started right off building by Dave's plans...

The main problem, in my opinion, that one encounters in making a resistance furnace is the structure that holds the elements in place. Dave's book describes one solution to the problem, and that is to form grooves in castable refractory.

My attempt at forming the grooves by Dave's designs failed miserably. The refractory that was suggested in the book was AP Green's Kastolite castable refractory, and after ordering and having shipped about a hundred pounds I got right to work. (Can you say 'UPS charges' 10 times really fast? Thank you. Now you feel my pain.)

Well, when I tried to pull the rubber hose out of the newly formed groove, the Kastolite chipped and broke out horribly. The element barely stayed in place in this malformed groove, but hey, I was following the instructions.

To make a long story short, I used the remaining Kastolite to make some 'donuts' with a little trough around the inside diameter, at the top. The inside of these donuts was the inside diameter of the furnace, and when stacked one ontop of another, nice, well-formed element grooves resulted. However, the making of these 'donuts' required some styrofoam cutting to make forms, and that's another story...

This method of forming the element grooves worked well indeed, and the Lil' Bertha was up and running at last. After a few melts, I discovered the great benefits of using electricity for melting. (I had indeed tried gas burners, but they were noisy, required close supervision, drank fuel like Coca-Cola on a hot day in the desert, and held the temperature about as steady as a roller coaster.)

The Lil' Bertha was a great success. I made a good many melts with 'er. However, the Kastolite began crumbling from the many heats. (An AP Green technical support rep told me that Kastolite was intended as a backup lining, and that I should have used Mizzou!) Well, the original Lil Bertha finally went south, so the rest of this page is devoted to the process of producing the New and Improved Lil' Bertha!

The Melting Corner

Another improvement that I made to the melting furnace is the controller. Instead of using a range control mounted right on the furnace body, I designed a beefed up version of a lamp dimmer and mounted it up away from the heat of the furnace. As you can see in this photo, the furnace and its controller are located in a corner of my shop next to the electrical panel.

There are a quite a number of improvements to be made to the original Lil' Bertha design. If you are considering building this furnace for your shop, you may be able to benefit from one or more of these improvements that I found useful. There are two that I consider the most significant: 1. Using hard firebrick for the furnace interior and 2. Making your own castable refractory with high temp mortar and perlite.

Detail of grooves in firebrick

Making grooves in firebrick is not as much a problem as first expected. I took three abrasive fiber masonry cutting saw blades and mounted them like a stack on my table saw arbor. I tilted the arbor to 30° and raised the stack of blades so they made about a 5/8" deep cut.

Straight grooved and terminal brick

Since the furnace was to use 6 firebricks in a hexagon, five straight-grooved bricks were made and one with angled grooves. When cutting the grooves, I cut each groove on all the bricks before making adjustments to the fence, and spaced the grooves on exactly one inch centers. The angled-groove brick serves as the terminal brick.

The firebrick dimensions are 4 1/8" x 8 1/4".

How the grooves in terminal brick align

In making the bevels on the edges of each brick, it took some extra attention to the angle needed to correctly align the ends of the angled grooves with the straight-grooved bricks.

Note how the path formed by the grooves in the bricks resemble the ramps in a big-city parking deck! This allows a single element to be used, spiralling from top to bottom.

Firebrick clamped together in a hexagon

I used long hose clamps to solidly clamp the six firebrick together. These clamps were left in place around the bricks and the refractory rammed in around them.

Wooden formers in place, ready for refractory

For the furnace body I used readily available galvanized 26 guage heating/cooling air duct pipe. The furnace is 12 inches in diameter, and so it used two 6" pipe sections snapped together parallel to each other to make one 12" round shell. I put srews and nuts through right at the seams to keep them from popping apart.

The wooden formers were handy to keep the furnace body nice and round while ramming in the refractory.

All you need to make your own lightweight castable refractory!

I wish I had discovered this very simple and durable formula sooner! I got the perlite at a local Wal-Mart, and the Worcester Brush High Temp Furnace Cement at a hardware store.

The recipe is very simple, it's just a 4 to 1 mixture, using 4 quarts of perlite to 1 quart of cement. I used two types of cement, the black 3000°F and grey 2700°F. There was quite a difference, and I recommend using the black stuff, it thins a lot better and is smoother.

Complete details of this do-it-yourself formula are available at John Wasser's Coffee Can Foundry site.

Rammed full of home made refractory

The refractory compresses a fair bit as its rammed in, so I had to be cautious not to ram it too hard.

Furnace lid before filling with refractory

The handles are garage door lift handles, and I attached them with the long carriage bolts that came with them. Also, I put two extra carriage bolts in, so there's extra reinforcing support for the refractory

Three legged furnace base before filling...

The legs are 1/2" galvanized water pipe.

Leg mounting hardware is also refractory support

Similar to the lid, and especially important here because the weight of a full crucible rests in the center of the base.

Making the refractory support wires tight

After having the bottom of the furnace base fall out several times before it was fully cured, I decided it was time to devise a way to support the very bottom of the base.

So a series of 1/16" holes were drilled all the way around the bottom edge of the base, and a pattern of wires woven so that there were no more than an inch square of unsupported refractory in any area. This solved the problem and also provides extra insurance against failure of the base under the weight of a full crucible.

Completed furnace base

This gives a better view of the base section with its supporting wires.

Preparing to fire the base and lid

The home-brew refractory steams a LOT while it's being cured, and this can cause it to soften and stick the sections together. So a liberal amount of baby powder (talc) was applied to the base first. It's probably still there.

Vent hole in lid

The vent hole was formed when the lid was rammed up. I used a 6 oz. dixie cup, rammed full of refractory (simply for support) to form this hole. (Note the tapered sides of the vent hole.) The dixie cup was removed after a few days of air drying.

Furnace height is 18 inches

Furnace measures a mere 18" tall and will handle a two quart crucible.

The handles are ordinary inexpensive garage door lift handles.

Melting a charge of aluminum

In this picture, I'm using the base and lid from the original Lil' Bertha while air drying the new base and lid. Also, the new furnace has a slightly deeper and bigger diameter chamber, so a larger crucible can be used.

Now you can purchase and download plans to build your own melting furnace!