I machined this jig from some ridiculously over-heavy steel I had lying around. The idea was to let students clamp it to a piece of 2x1 extrusion and drill the standard half-inch-spaced holes with a #7 bit, something we do a lot.
It mostly worked, but because I made it out of mild steel it started to wear. I think I eventually drilled out the holes and pressed in some hardened bushings.
Printed versions (fall 2023)
To address the issue with the above unit wearing out, in October 2023 I made a couple of 3D-printed versions. First up was a prototype. It shows one of the drill bushings that I made to guide the drill, since if the mild steel I was using on the original version didn't stand up, the plastic definitely wouldn't.
My 3D printer has more than enough accuracy to place the holes. I measured the prototype and found it had placed that bushing to within 0.001" of the correct location, and since the bushing is reamed, the whole thing is probably within about 0.005" as far as putting the hole in the right place.
Of course, jigs get abused. The kids broke one and I broke another. In early November, I think this was at least version 5. Visible in the fifth hole from the left is the locating pin I made, so the jig can be used to make series of holes that are longer than the jig.
