Here is a very close up view of the rotary spark gap and its cooling chambers. The green disk is made out of 3/4" high grade Phenolic 16" in diameter. I mounted it to the 3 hp motor. It was then trued up by slowly turning it and grinding the face, back and edges with a Foredom rotary tool. It took almost 1-1/2 months to get it true and a lot of grinding bits, I have never seen anything so tough as this material unless you use carbide bits they would dull and stop working after 5 minutes. Carbide bits lasted about 24 hours of accumulative use. After the disk was true I then drilled 8 holes evenly spaced at 12" diameter. This is were the aluminum sleeves were installed to hold the tungsten rods. After it was completely assembled I had to balance it, the whole thing was only off about 1/2 ounce on one side. Speed was slowly increased and held for 15 minutes at a time until 4,000 rpm was accomplished, It was then ran for 2 hours at 4,000 rpm to be sure it could hold up to the tremendous kinetic forces. During the test I controlled the speed of this AC/DC motor with a variac and monitored the speed with a digital rpm gauge. I now have a voltage to rpm chart that I use to run the rotary spark gap it is accurate to within 50 rpm's. The brown cheaper grade Phenolic plate 1/2" x 18" square holds 8, 2-1/2" aluminum cooling chambers for the tungsten rods. Each has a red rubber hose connected to it, and to a oil chamber reservoir.