I have just finished the HV switch for my quarter shrinker. It is very similar to yours with the 2" brass electrodes. I was very careful in construction and am quite proud of it. I can achieve a gap spacing smaller than 1 mm with excellent parallelism. I use strictly spring loading for triggering with a string (no electronics for safety and reliability).
My next step is the blast cage construction which leads to my question. My current design concept is a 12" x 12" x 12" box made of G10. The floor will be 1" thick. The walls and top will be 3/8" thick. The corners will be reinforced with angle iron. Does this seem adequate? I also want to make some holes with baffles, to prevent fragments from exiting from the top, to relieve the pressure from expanding air. What do you think of this?
I also want to mount the copper electrode holders on two 5" tall by 2" diameter ceramic insulators inside the box. Do you think the ceramic will hold up to the copper fragments or will it be chipped away? Thanks in advance for your advice.