Rainy Day - No Kites to Fly

I've been on vacation for the past week, but the weather has been rainy and I've had a cold most of the time. So I've been out a total of two times with my kite gear, and I have very little to show for it. I could be depressed, or...

I could start a shop project!

Ok, to be fair I finished a shop project. This one has been hanging around for almost a year now: the new kite line winder. I started CAD drawings last year, beginning with a design that's sold commercially under the name "Windbreaker". One of the people on the KAP forum described it as "Knucklebreaker" because of the handles, bits, and pieces that hang out when it's rotating, so I moved away from it. Erick, one of the KAPers from Germany, posted pictures of his winder, and I liked it. So that's the direction my CAD drawings went.

A few weeks ago I picked up the 1/2" baltic birch plywood I needed for the project, and I finally got around to cutting out parts. Over the last week I've sanded, tung-oiled, and finished building the thing.

(Yes, that photograph was taken outside my house... in the rain... It really hasn't let up much.)

It's heavier than my old winder, but a lot more solid and way easier to hold. I haven't had the chance to field test it yet, but if the weather clears any time in the next few days that's my top priority.

The center grip is a wheel off of a scooter that was run over by a car. The bearings are still good, so I stuck with the originals. If they start to go, I've got a tube of ABEC7 bearings I picked up to replace the ones in my Foredom handpieces. That was years ago. Dang Foredom makes a good product.

The winder handle is a piece of 1" diameter Delrin, bored out to ride on a stainless sleeve that's pinned in place by a 1/4" bolt. The design for this part started out using bearings as well, but there's really no point since Delrin is a bearing material, and it rides great on the stainless. So the design was simplified. I tried to make it comfortable to hold, but if it needs adjustment it's a simple lathe job.

The row of holes out toward the edge of the winder is so the line can be clipped off with a carabiner to fix it to a particular length. This lets me put out, say, 200' of line, clip off, anchor, and attach my rig.

So far I'm pleased with the winder, but it does mean changing some of my procedures in the field. My previous winder had a hole clear through it, so it was pretty easy to clip off the line, shove the winder up onto my arm, and use both hands to hang the rig or use the transmitter. This winder won't allow for that, so I'll have to work out new procedures.

I do like the larger moment arm on the winding handle, and the free-spinning bearings on the grip. I think it'll be a lot easier to bring line in. That might offset any inconvenience the lack of a through-hole will present. Time will tell.

I'll write more once I have a chance to field test it.

Tom

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