The Foundry Furnace

It all started when I found a book titled: "The Dividing Head & Deluxe Accessories" By David Gingery in the local library. A second trip back to the library a week later turned up "The Metal Lathe" also by David Gingery. He wrote a series of seven books to serve as a guide to building your own metal shop from scrap aluminum. Using the an address I found in the book I wrote David and ordered the entire set including the "Building a Gas Fired Crucible Furnace".

I decided to build the machine shop out cast aluminum as described in the books. I had an advantage that I already had a good sized drill press and a small Unimat DB200 and the usual collection of hand tools along with a well equipped wood working shop.

One item I didn't have was a wood lathe, useful for making patterns that would later be turned on the metal lathe so I borrowed ideas from Fine Woodworking magazine and whipped one up over the Christmas holidays. The spur drive and dead center were purchased and I had a friend thread the tailstock.Homemade wooden Wood LatheWood Lathe Drive

In order to cast the bits needed for the lathe I decided that the Power Hacksaw designed by David's son, Vince, would be a welcome addition to my shop. I made an inventory of all the steel required for the projects and bought them at my local Metal Supermarket. Some of the hacksaw frame I gas welded and the rest I had a friend MIG weld. The result is a power hacksaw that can cut unattended and leave me to play in the shop while the metal bits are being created.HackSaw

With the hacksaw complete I started cutting the various bits of hot and cold rolled steel that I would need for the lathe, mill, shaper and furnace frame. The furnace requires several round forms to hold the castable refractory so the Slip Roll seemed like an appropriate project and this took several years and a move before I completed it. Only after using a metal cutting bandsaw was I able to finish cutting the 3/4" thick end plates. Once again a friends milling machine helped make things exact but as it turned out the precision wasn't as critical as I thought as the rolling former worked well even with the small alignment errors. The same friend did the MIG welding and with the completed Slip Roll was able to create the forms for the furnace seen behind the roll.Slip Roll

I dusted off the hacksaw at this point and cut the raw materials for the foundry frame. After a quick trip to the welding supply house for a refill on my gas welding supplies and I welded the base frame together. My MIG equipped friend welded the bits that were unworkable with Gas due to the furnace design. Three bags of 2800 degree Ladlecast refractable and a few hot days doing the preliminary baking in the household oven finished off the furnace.

At this point I realized that the almost 150 lbs of furnace and fan would be too difficult to carry around so out came the hacksaw again. I borrowed a small 125A MIG welder, picked up a helmet and taught myself to blob filler material onto Hot Rolled Steel. The frame with casters and the burner assembly are the result. With a width of lest than 28 inches it will fit through most standard doors and will ultimately sit underneath the molding bench.

Propane Crucible Furnace

Click on the photo above  to see a larger photo of the burner.  You can just see the small Micro-processor based controller by the FAN.  The micro is based on a CANDIP (  which uses an ATMEL 8515 uC and has RS232 and CAN outputs.  There are 3 power transistors: one for the Spark plug coil drive;  one for the Gas Solenoid and one for the PWM motor control.

The furnace is started by closing a contact which starts the motor turning at slow speed;  enough to just create airflow into the furnace body.  A flow sensor checks for air movement and if it's there then starts the spark plug device generating a spark every 10ms.  A short time later the gas solenoid is turned on and if the flame detector sees UV light it then stops the spark and speeds up the motor to burn speed.  Then entire operation during testing would take almost 15 seconds but the latest tests have it igniting within about 5 seconds.  If the UV detector sees the flame vanish then the gas solenoid is closed and the FAN speed increased to a high rate purge cycle for 10 seconds.  Then the fan speed is dropped back down to ignition cycle and the processor tries to relight.  Three strikes and no flame and a shutdown is forced.

Furnace BurnerBurner Assembly

With the squirrel cage fan a reasonable blue flame was created inside the furnace but the air resistance with the plug for the lid installed caused the furnace to extinguish regularly. Plug for Furnace LidThe theory at the moment is that the junction between the Burner Pipe and the Venturi section causes turbulence and as the furnace heats up and combustion backpressure increases the flame front moves into the burner pipe. It appears that the squirrel cage is not powerful enough to sustain combustion and propane pressure cannot be increased above 4.5 PSI.

So why build a machine shop? Two reasons. The education received while fabricating the tools is immeasurable. Tools that make repairing things like this:

AeromotorAntique Motor

There's more to come... stay tuned.