This is an experiment. I was recently putting in a materials order and I noticed in the ‘odds and ends’ department they had ¾” threaded maple dowel rod. For a few dollars per lineal foot, I thought it would be worth putting in the cart. When it arrived, I set out to build a double screw.
I grabbed two pieces of cherry I had laying around and drilled holes for the screws. First I drilled a pilot hole where the screws would go. This gave me my alignment between the two jaws. Then the outside jaw was drilled with a ¾” hole so it would free float on the screw. The inside jaw was then drilled about ¾ of the way through with a 1” forstner bit. Before breaking through, I switched to the ¾”bit to exit out the back just big enough for the screw.
Now that I’ve got a gaping hole where I need threads, what’s next?
I drilled some ¼” holes around the inside perimeter of the hole. (Wait. More Holes?) These holes will get filled with epoxy putty and when the epoxy cures these “teeth” help keep everything in place. Once the hole was pretty well full of epoxy, I used my (liberally paste waxed!) threaded rod to turn my way through. Once it was through, I made sure to mash a bunch of epoxy back down in there to surround the threads. Over the next fifteen minutes or so I would turn the screw back and forth a few times just to make sure the threads were established well. As long as the screw is waxed, the epoxy won’t stick to it.
The next day I turned a couple simple handles, bore out an oversized hole in the middle, and used epoxy putty to permanently attach the screw into them. (Don’t wax that end of the screw! ) I toothed the jaws of the vise for better grip and the next day I gave it a go. It works wonderfully. For small work, the ¾” screws are fine and because the threads are epoxy they are super strong.
This may all sound convoluted. I know if I were reading this, I would be saying, “Why don’t you just get a tap and die set?” The answer is: this was a quick and fun experiment and it’s a way to use materials laying around the shop to make something that works just as well (hopefully... this is an experiment, you know). I will be getting a tap and die in the near future but this was fun in the meantime. The second answer is that I am curious to see the holding power of epoxy internal threads as I imagine this being useful information for my conservation work.