Mark my word

I always love discovering new tricks. Here's the latest.

I don't have a jig for drilling eyeballs. I'm not a great woodworker, so I've had to make do. Usually I get close enough. Nevertheless, I'm always trying to improve my precision. I use wood knobs that already have a starter hole on the flat side. It's pretty easy to drill that hole accurately the rest of the way through on a drill press. The harder part is drilling a precisely-centered hole on the side where the self-centering springs go. Measuring a rounded edge is really difficult.

Here's what I figured out. If I place two wood knobs flat-side down and touch the two together, the part touching is exactly half-way down. So I took a small piece of paper and drew in a small field of black on both sides of the paper using a Sharpie. Then before the ink dried, I slipped the paper between the two wood knobs flat-side-down and pressed the two together. The wet Sharpie ink made a mark on both knobs exactly in the middle where the two knobs touched.

Now I have my mark to drill the holes for the springs.