This is an index plate for a dividing head http://en.wikipedia.org/wiki/Indexing_head, used with subtractive processes on milling machines or lathes. I wanted to see if I could make a plate with different combinations of holes than were available, but still need to check the dimensions of the center hole and total diameter for compatibility.
The rings of holes are primes (13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 52). You can use a geared mechanism to divide a circle into any number of parts. For example, making a N-tooth gear, or cutting M faces on a solid. For an idea of how they work, see http://www.atmpage.org/contrib/JSAPP/divide/divhead.html or http://gearcutting.blogspot.com/2008/02/dividing-head-settings.html.
I haven't published the source file (yet) because I ended up doing this in a way that seems really crude. Once I figure out how to loop the right way the code will be a lot cleaner and easier to understand.
This is the first step in building a simple dividing head.
Just a flat cylindrical plate that mounts on an arbor.