Miscellaneous Thoughts and Musings: Making a Toy Gyroscope on a Mini-lathe

(Change of pace for this post.)

Last year I bought myself a Chinese-made mini-lathe (SIEG C3) to play with, similar to the small metal-lathe my father still has in his workshop. I've been doing a few small projects on it, including some spinning tops and simple tools, and decided to try making some toy gyroscopes.

I was inspired by the toy gyroscopes I had when I was a child: you would up a piece of string round the spindle and pulled to get them spinning. They used to come with a little plastic "Eiffel tower" that you would balance them on. I wanted to make something a bit more "serious" than those.

Prototypes

I went through a series of prototypes, starting with some 1 1/2" diameter brass rod. My first attempt didn't have nearly enough angular momentum, so I switched to using much thicker slugs of brass. For the last prototype I bought a piece of 2" brass rod on ebay to use. I also decided they needed an outer cage to allow them to keep spinning when held.

I tried various bearing options, including a simple point-and-cup bearing, miniature thrust bearings and regular cartridge ball bearings. In the end I find that the 1/4" ball bearings purchased from VXB worked best (about $3 each).

This page show the final version I made for my brother's birthday, using a 2" diameter flywheel. I also made a couple of smaller ones for my daughters for Christmas:

Raw materials

The raw materials were:

2" diameter brass round bar for flywheel
2 1/2" OD brass pipe for cage
3/8" brass bar for bearing cups
1/4” stainless rod for spindle
2 X .25" OD/.125" ID bearings

(Note, the dimensions for materials are in inches since that's easier to order in the US. All my working measurements are in metric however, which is much easier to actually work with.)

Part 1: The Cage

The cage is probably the hardest part to make. It consists of two brass rings with notches filed in them to snap together. The inner ring is drilled and threaded for the bearing cups.

First cut two rings from the brass pipe:

Next, face the sides of the two rings and turn them down to 8mm width. Make sure the sides are parallel:

Turn the outside of the pipe off to make it round and get a nice finish:

Now switch to the outside jaws on the chuck, and bore out the inside of the rings to the desired thickness (I did 2.5mm).

Optionally curve the outside surface of the rings. For this switch back to the inside jaws and set the compound to a small angle (5-10 degrees). Finish with a file and emory paper:

Next we need to drill and tap the holes in the inner cage for the bearing cups (M4). It’s important to get these correctly aligned. This could be done with a drill press if you’re very careful, but I found it better and more accurate to drill and tap on the lathe using a 4-jaw chuck:

I also used a tap-follower, which I had made for the purpose, to make sure the tap was straight. You can buy them of course, but they’re easy to make and a nice side project.

Finally we need to file notches in the two rings to make them fit together. These should be the same width as the rings (in this case 8mm) and slightly less than half the thickness of the rings, so that the rings are squeezed/stretched when together. The notches on the inner ring should be 90 degrees from the holes. The sides of the notches on the outside ring should be sloped slightly as they will go in when the ring is squeezed.