It’s not too hard to find vintage wooden screws on the second-hand market. Between antique stores, tool swaps, and eBay, there is usually a handful of inexpensive options. The problem with many of these survivors is that the nut is either trashed or missing altogether. Unfortunately, because these screws are not universal sizes, it’s not as easy as buying a replacement nut. So, how in the world can a totally sound screw be put back in service? How can a nut be made that matches the thread size, count, and spacing exactly? The answer, for me, has been casting.
A few years ago, I began experimenting with the use of “tootsie-roll” style epoxy putty sticks to cast threads for regular shop use. I bore an oversized hole so that the screw can slide in and out with ease, and then bore a series of ¼” deep holes around the perimeter to provide a place for the epoxy to lock into. After thoroughly kneading the putty, I pack the holes with putty and let it mound up with enough material for the new threads.
After heavily paste waxing the screw’s threads, I begin slowly twisting the screw into the putty, manually advancing to match the thread spacing. Go slow. And don’t rock the nut as you twist.
You can’t simply cast the threads in one location on the screw and expect it to work, because these threads need a bit of slack in the fit. To get this looseness of fit, every couple minutes, over the next 5-10 minutes curing, I slowly turn the nut one rotation. This accounts for dimensional variations along the length of the screw and ensures that the epoxy doesn’t stick to the screw... even though you’ve heavily waxed the threads. (You didn’t ignore that step, did you?). To make sure the nut is cast square, I keep checking against the screw, and even clamp a square if it wants to tilt as it cures. The excess putty will ooze out the back of the nut. I just squish it around the screw and embrace the extra thread depth.
After about 15 minutes, the putty is hard enough that I can’t get a fingernail to imprint. I leave it overnight before putting any serious pressure on it.
But is it strong enough for real use? You betcha. When you consider that the original wooden threads had a ton of weak endgrain, this epoxy is more than sufficient for the task at hand.
This method means that another vintage screw was restored to noble use, just in time before Cracker Barrel stuck it to the wall.