Toys from the Shop

Having a home shop isn't all about making tools or making parts. Some of the most rewarding projects I've done have been toys, or repairs for toys. With the holidays drawing on, it's fun to make toys in the shop to share as presents, or simply to share as soon as they come off the lathe or mill.

A little while ago I got back into making tops. Nothing advanced, just something fun to make on the lathe and share. It's the kind of thing anyone with a few shop tools could do. I did this one on a Taig lathe, which is a small benchtop lathe originally designed for making contact lens molds. I've never used mine for work as fine as that, but for things like this little top it's ideal. The same kind of thing could be done on a drill press with some files and a little more time, though.

The big trick with tops is that everything has to be coaxial. If you have any part of the top off the centerline, the top will wobble. Wobbles rob the top of kinetic energy and make it spin for a shorter time. The more concentric and coaxial you can make it, the better.

For this one I chopped off some 1/8" diameter brass rod, chucked it in a collet chuck, and cleaned up both ends. I then drilled some 1" diameter Delrin undersize and pressed the rod in place. The assembly then went back in the collet chuck. I also chucked up a bearing with a 1/8" ID hole in the tailstock, and brought that in as a live center to support the outboard end. The body of the top was then cut using an 0.060" parting tool. Not the best way to go about it, but it got the job done. I wasn't all that careful about the actual depth of cut, but I made each pass in 0.050" steps.

This top will easily spin for over a minute. It's not that hard to do, and the kids have a blast with them. Larger tops will have longer spin times, and certainly better thought out ones will spin longer.

For the ultimate in spinning top design, look no further than the mathematics for calculating steam engine flywheels. Ever wonder why the flywheels on steam engines are spoked? If you look at the math for the kinetic energy of a rotating annulus, you find that for a given outside diameter, there's a break even point on the inside diameter where you stop benefiting from additional material. Inside that ideal ID, steam engine designers would spoke out the wheel to cut weight and save iron.

The fine-tuning of spinning top design reached something of a pinnacle in the Quark, a top designed by Jim Lewis, who incidentally also started up the eMachine Shop company. What sets the Quark apart, aside from being a very efficient flywheel design, and having a shaft that is designed to get the most speed as possible out of the human fingers, is that it can be dynamically balanced to remove almost all residual wobble. The tops come with a laser pointer and a set of counter weights that can be installed in pockets underneath the outer rim of the top. By reflecting the laser light off the top surface, it's possible to visualize the wobble in the top and balance accordingly. Spinning times of fifteen minutes or more are common.

But they also take considerably longer to make, and are made to much tighter tolerances than my little Delrin and brass top. For the purpose of cranking something out in the shop you can hand off to a kid and watch them have fun, sometimes the simpler approach is more effective.

Tom