Rotary Gap Construction Details

• Side Plates -------------- 1" thick acrylic, 14"x14" square
• End Plates --------------- 1/2" thick polycarbonate
• Base Plate --------------- 1/2" thick polycarbonate
• Rotor (disk) ------------- 1/2" thick G-10 (Epoxy-fiberglass composite)
• Shaft ------------------- 1/2" electric motor shafting
• Stationary electrodes ---- 1/8" TIG welding electrodes
• Electrode holders -------- turned aluminum
• Electrode holder holders - turned phenolic resin plastic (bakelite)
• Bearings ----------------- Sealed ball bearings
• Pulleys ------------------ Salvaged from furnace blower
• Electric motor ----------- (Not the one shown on any photos) 1 HP 10,000 RPM Carter motor 110v AC/DC
• Moving Electrodes -------- 24 1/4-20 Brass Acorn nuts (2 each side)

I designed the rotary gap mechanism this way so that it would satisfy several requirements.

• Ability to change motors relatively easily
• High electrode velocity
• High break rate
• Bulletproof enclosure to contain exploding disks, etc.
• The electrode holders must be able to get extremely hot (300F, ~175C)
• The electrodes must have adequate heat dissipation available.
• Variable speed

The large motor shown in the photos is not the one that I finally settled upon. It was single speed induction motor, and therefore I could not adjust its speed. I used it because it was handy and I had no other motor at the time.

The motor that I am using now is much more powerful and faster as well. I can vary the speed of the disk from 0 to about 5000 rpm, which is more than fast enough.

Because the electrodes would get hot when running at high power levels, I decided to hold them with large aluminum holders. They are turned from 1.5" aluminum rod. I was also concerned that they would get hot enough to soften the acrylic side plates. To get around the problem, I made some phenolic bushings from pieces that I had around the garage.

I have used this rotary gap in coil operation and it works quite well. It is quiet, which is Oh So Important when running a tesla coil :-) (In case you aren't aware of it, a tesla coil is extremely noisy.)

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