scan0002.pdf
scan0001.pdf
Here is the simple drawing I made to help me as I went. You could adapt it to any size to fit your needs.
The tool picture is what I found that inspired me to make mine.
The parts list I used is as follows.
2 @ 1/4-20 barrel bolts that are 3/8" x 3/4" long. I bought a few of these and I'm going to start using them on my mortise and tenon bolt on necks instead of using threaded inserts. I have since found some online where the hole is in the center of the barrel, unlike these where it is offset. For this purpose, that worked out better.
About 2" of 3/16" rod
1/4" bronze bushing (3/8" outside dia)
1/4-20 bolt, washer and wing nut for locking
3" long 1/4-20 threaded rod
1/4" lock collar
Threaded knob and a locking nut.
Hardened 1/4"x 1 1/2" long pin for the centering pin.
I also put a bushing in the workboard for the pin.
The slot for the locking bolt is 1/4" wide.
The slot for the top sliding adjusting part is 3/16" wide. The is because I drilled 3/16" holes in the bottom of both barrel bolts and press fit in a section of the 3/16" rod. Then I drilled a 3/16" hole in the base for the threaded barrel bolt and in the end of the top sliding part for the barrel bolt that is drilled out to 1/4" so the threaded rod can slide through it. These are just pressed into the Plexiglas. I later wicked in a little CA to help them hold but they go in very tightly.
That is pretty much it. The length of the slots and the distance of the centering pin to your routing bit will determine how small and how big a circle you can cut.
I cut the slots on my drill press using the router bits needed. I double side taped the Plexiglas to a piece of MDF the exact same size and clamped it into a cross vise on my drill press table, enabling me to cut them as you would on a mill.
This is a quick and dirty explanation, hope it helps.
Fun to make pretty easy too.