Twisty Toy

I designed this simple twisty toy based on an epicyclic bar angular transmission. It's a cool little fidget toy that looks like it shouldn't turn. Works well as a stress reliever!

You can make this toy with either a wood lathe, or a 3d printer, or a laser cutter.

Hardwood like maple and cherry

1/8" brass rod

3/8" dowel

CA glue, wood glue

If you have access to a 3d printer then the easy version of the Twisty Toy is 3d printed. The files are included. 3d print the two barrels and clean/drill the holes with a 9/64" bit so that the brass rods insert and turn easily. Cut seven 5 inch long 1/8" diameter brass rod pieces and bend them 90 degrees in the middle. Then insert all of them into one of the barrels first; and one by one into the second barrel. Nice little puzzle right there! To make the toy permanent and prevent the barrels from slipping off you can use CA-glue to glue a couple of short stops onto the two center brass rods. That's it. You are ready to fidget during your next Zoom meetings!

The prettier version uses wood barrels. I laser-cut a number of 3 to 5 mm thick cherry and maple disks (file attached) and then stacked and glued them into two 1-inch tall barrels. While gluing align the disks with two or three brass rods and check that the stack is straight up - not skewed. When the glue has dried, clean and redrill the 7 holes with a 9/64" drill bit so that the 1/8" brass rods turn easily. Make the brass angles as described in the previous step. Then trim, sand, and polish the outside of the barrels on a lathe (or drill press). I also made some spacers and end stops from a 3/8" maple dowel to CA-glue onto the center brass rods.

Without a laser cutter or 3d printer you can make the barrels on a lathe and drill the holes with your drill press. It should be obvious how to do this. The spacers and stops can be made from a 3/8" dowel.

For variety you can make bigger versions of the toy, or versions with fewer brass rods.

Cool animations of the underlying mechanical linkage are here:

Angular Transmission

Epicyclic Bar Angular Transmission

(Edit 2/21/2021) I just learned that this is also called a Hobson’s Joint, and I found this cool video of a Lego build:

Hobson’s Joint

Anyways, I'm still amazed that the toy actually turns! Enjoy!