The screws used to keep this together are regular machine screws, but the nuts (they’re called nylon lock nuts) have a plastic ring inside so they don’t come loose with repeated expanding and folding of the mechanism.

Awesome Kriss! Your approach is so different from many others and I always look forward to your innovative ideas. -Thanks.

1/4-20 x 24-inch Threaded Rod 1/2-inch Birch Plywood 1/4-20 x 1-1/4-inch Machine Screw 1/4-20 Nylon Lock Nut 1/4-20 x 1-1/2-inch Machine Screw 1/4-20 T-Nut 1/4-20 Hex Drive Threaded Insert 1/4-20 Hex Nut 1/4-inch Screw Washer

This rod does double duty because it’s also what spins the wooden dowel around. So basically when you rotate the threaded rod, you rotate the wooden dowel, and as everything is rotating, the pantograph mechanism pushes the dowel across the router bit. That gets you a threaded wooden dowel.

90-Degree V-Groove Router Bit Festool MFT/3 Multifunction Table Festool Screw Clamps (2 pack) Festool Ratcheting Quick Clamp Woodpeckers 24” T-Square DeWALT DW611 Router Kit Bessey 24-inch K-Body REVO Clamp

The segments that form the pantograph are made of 1/2-inch plywood. Each has thirteen 1/4-inch diameter holes spaced 1-inch apart.

What the ratio means, in this case 3:1 is that taking the distance here to be one unit, this distance is triple that amount. So any change in the diagonal distance for the small section, will be magnified three times in a large section – for a total end-to-end scale up of 4.

The size of the pantograph is precisely controlled with a metal threaded rod. Spinning the rod advances it through the threaded insert in the middle, and that pushes out the block in front. That enlarges the small section, and geometry of the pantograph takes care of the rest.

Now putting the skewer together. First, a block with straight through clearance hole, then the threaded insert block, some red pepper, two regular hex nuts – I’ll tighten these against each other so they can’t move, a washer, another block with straight through clearance hole, another washer, and finally a nylon lock nut.