Mark I
Simplistic Design. Abysmal Failure
The Mark I Furnace design, if you can call it a "design" is as simple an electrical circuit as you can get. It was entirely manually operated and designed off of pretty much every other "Arc Furnace" design available anywhere on the internet. Calling it an arc furnace is like calling a single engine piston a supercar.
The principal looks something like the diagram below. It is strictly alternating current and is about as effective as a metal melting tool as a ping pong ball is useful as a ball bearing. I include it here mainly so that others can avoid trying this hazardous and pointless exercise.
As simple as it gets. In this case, the transformer I was using was an old transformer from an Uninterruptible Power Supply and had two coils around one core. I wired them together in series for an open circuit voltage of about 60V AC. There was also a fuse in the case which isn't shown here. It blew constantly as there is no way to control current in this circuit.
Test run. The switch and transformer can be seen in the box on the left with the leads coming out. Graphite electrodes were used to generate the arc which was very fluttery at these low amperages and difficult to maintain. The low amperage had very little effective metal melting capacity aside from surface erosion. I don't recommend that anyone try this. It is pointless and actually quite dangerous.