Turning Bikes and Trees 2

Two of my lifetime passions are cycling and woodworking, bicycles and wood. I am inspired to look for interesting ways to integrate them. Here, for example, is a slightly rusty freewheel sprocket and a nice quarter section of black walnut.

My intention was to turn a sphere and bisect it with the sprocket.

The first thing to do is rough the wood down. I marked and punched the centreline I wanted at each end of the log, then bandsawed away a big chunk of waste and mounted the blank on the lathe. That's the roughing gouge sitting on the wood. It chips and peels the wood away very quickly, and doesn't rely on the work already running true for a good cut. You can just pass back and forth, sending chips flying. Eventually you will have a cylinder.

I wanted to start with a diameter similar to the gulleys of the sprocket's teeth, so I set a pair of calipers to that dimension. The parting tool is lying across the calipers, as I planned to use it to establish the diameter.

I laid out the sphere with three pencil rings, intending to leave the centre one and turn down to the outside marks. Partway there, I noticed a large split developing at the tailstock end. I stopped, flooded the crack with cyanoacrylate glue, and tightened a hose clamp around the end. (I removed the hose clamp before resuming turning! It's just posed on the lathe like this.)

I had time to think, and decided that I had better make myself a half-circle template if I was to have any hope of achieving a sphere. As it turns out, the diameter I'm eventually looking for is about 2.5 inches, and I have a hole saw in that size. I made a quick plywood template and used an orange pencil crayon to mark the highest spots.

Mark, turn away marks, mark, turn away marks... it didn't take long to get quite close to spherical. By this time my vision had changed and I wanted to leave the sphere on a simple footed post, and then set the sprocket at an angle.

I had used a square scraper to peel down the post, and now switched to using it instead of the gouge on the sphere as I crept up on the shape.

I sanded to 240 grit on the lathe and then parted the base off. I made a hash of the parting off, and the bottom of the base was indeed undercut but also badly scored. I mounted a sanding disc in a Jacob's chuck and cleaned up the base, doing penance for my turning error.

Now I had to figure out how to slice through the sphere in a straight line at the right angle. I didn't want to use the tablesaw, because I don't have a thin-kerf blade and don't want the sphere to become squashed. So I decided that meant a jig on the bandsaw and sanding to fit.