Magnetic attraction opens your eyes to the blind hole
If you’ve ever built a bed using traditional bed bolts, as shown above you know how difficult it is to blindly match the bolt-access hole to the bolt hole in the rail. Misalign the two holes even slightly, and the nut won’t slip over the bolt threads. Here’s my method to perfectly mark the centerpoint of the bolt access hole.
After drilling the bolt hole in the end of the rail (but before boring the access hole), slide the bed bolt into it. Now roll a cylindrical rare-earth magnet, or a stack of flat, round ones, over the inside face of the rail. The magnets will be drawn to the internal bolt and “find” it by coming to a rest directly over the bolt. Mark that location and repeat, moving the magnets farther from the end until they no longer attract. You have located the end of the bolt. Mark a center point there and drill the access hole.
—Mike Schupp, Prairie Village, Kan.