Q:

John White used Allen-head screws to level his router table (Space-Saving Router Table, FWW #216). Did he use a tap for threading metal to tap the plywood? If not, how did he do it?

Greg Lowery, Amarillo, TX

A:

I did not use a metal tap, because they do not cut threads in wood very well. Instead, I used a bolt with the same diameter and threads-per-inch as the Allen-head screws. I filed the tip of the bolt to a taper. The shopmade tap can be used like that, but to get cleaner threads, use a hacksaw to cut a slot that runs the length of the tapered section of the bolt and just into the threaded portion. To use the tap, drill a hole 1/16 in. smaller than the diameter of the Allen-head screw and slowly drive the tap into the hole. I use an impact driver but a wrench works, too. Use a few drops of paint thinner to lubricate the tap and get cleaner threads. If the tapped hole is too tight, run the tap in and out a few times. However, you don’t want a loose fit, because the wood actually acts like a nylon insert stop nut, locking the screw in place against vibration.

Photos: Kelly J. Dunton