Based on http://www.thingiverse.com/thing:802145, this customizable scad file will produce concentric rings, pinned together, using a variable angle between the pins. The original used 90 degrees, where this version will allow you to select the angle between each ring's pins, ranging from zero to 180. Please see the original, referenced above, for suggestions to improve the printing. (Note that currently, the holes don't line up with the pins (except at 90 degrees), so consider this a work in progress.)