3600 RPM, 120 BPS
Synchronous Rotary Spark Gap
This is the simplest rotary spark gap I have come up with to date. It avoids Tungsten cutting of any kind and reduces the necessity of making the rotor with perfect alignment. If the electrode is not very perpendicular to the shaft, it does not matter that much. Just don't get sloppy. You should still try to make a good rotor.
The parts are:
1 - Teletype motor for $20 from eBay (3600 RPM synchronous).
1 - 2" long piece of 1" square polyethylene rectangular bar
3 - 5/32" thick, 7" long Tungsten electrodes
The electrode holders are attached with just 1 screw up from the bottom. They can be turned slightly to set the electrode spacing.
Although I strived for no Tungsten cutting, the electrodes sticking out the back tend to make the phase adjustment a bit dangerous. I'll either add an extention bar of some sort, or maybe just cut the electrodes short.