To design this jig, I dissect the motion of cutting a wooden thread into two components: a vertical component, and a rotational component. So if you can imagine, when you have a router bit, in order to cut this thread, the bit needs to circle around and move down to advance to subsequent layers.
For the vertical motion, I designed this system that uses a lot of hinges to ensure that this platform is always parallel to the surface below. So now with a machine screw through here, there’s precise control of the vertical position.
For the rotational component, a router will be mounted to this circle (off center) so that when this circle goes into this hole, and as you spin it around, the router bit will follow a circular motion in accordance with the diameter of the screw thread.
Using a keyhole router bit like this one, that will create just the pattern that’s needed for a square thread.
All that’s left is to control the relationship between vertical position and rotational motion. For that, gears! But because this little gear will be moving up and down relative to this surface, this spacer is required to ensure the gears mesh. So let me put all this together, including the router, and then we’ll take a closer look at how the bit moves.
Here is what the cutter will look like.
Here’s the build process: I’ve already cut out the basic shapes, which are 2x 12″ squares, and 4x 12″ by 2″ rectangles. The most difficult part really, is cutting the gears. Watch my video from last month to see how I did that.
With the specifics of the router mount taken care of, I move on to create the spacer for the big gear. The router table circle cutting setup is pretty great.
Screws will secure the spacer to the smaller circle below. I chose to use machine screws, and although I only show drilling pilot holes, off-camera I tapped the threads and countersunk the side of entry so all hardware sits flush with the surface of the wood.
Here’s a head for that holt… and the moment of truth.
With the edges chamfered, there’s the bolt and nut in final shape. Well, that turned out pretty darn cool. I hope you enjoyed it!
Now I don’t have any idea what I’m actually going to do with these wooden hex nuts now, but if you have any thoughts I’d love to hear about it in the comments! Otherwise, I don’t have plans available for this jig, but I hope I went through all the details you need if you decide to make your own version. Of course, if you have any questions feel free to contact me and I’ll do my best to help out. Otherwise, until next time take care guys!