A big aluminum spark plug!

[bobs409]

For the man who has everything, a big aluminum spark plug! Got the idea and had to have one.

I opted to use the old style R45 AC plug that used the 13/16 socket as the model. It has more of a fat stubby look unlike the thin 5/8 variety. Using a digital caliper, I made countless measurements of the real plugs width and spacing's and multiplied each of those by 53%. The reason I went with 53% is so the hex area would finish up at 1-1/4 and that was the magic number. This was machined from a piece of 1-1/2 round stock a little over 4 inches long.

The side electrode was made separately and installed at the end into a #50 hole using JB weld for aluminum. Everything else was done on a mill and lathe.

It helps to have a sketch sheet with the measurements laid out as there are so many ways to screw up! Luckily I had no troubles but there is a lot of math so it's best to prepare that ahead of time. (I would occasionally double check my measurements as I made them too)

The first pic shows the finished plug and below that I'll put in some shots of how it progressed.