Originally Posted by
El Heron
To fabricate the adapter I bought a 4mm thick 7075 Zicral aluminum plate off of eBay for $35, an entry level drill press, a $20 CNC router bit, a 10mm drill bit for the chainring holes, and a set of metal files.
A word of warning to any who may wish to do the same:
Do NOT use a drill-press to do milling.
I suspect that the op may have done this and got away with it ("entry-level drill press" and "router bit").
Here's why:
Most drill press chucks are mounted on a taper, the chuck has a socket, the taper sticks down from the drill shaft. This taper is not designed to hold when side-forces are applied. Milling (other than plunge) is 100% side-force.
If it lets go - and they do - there are lot of things that can happen suddenly, none of them good.
A much better solution would be to chain-drill the outline of what you don't want, cut it out with a hacksaw, and file to your line. It'll be quicker and you should still have ten fingers.