I wanted to experiment with making a ball bearing out of wood on the lathe. Marbles make good balls for this sort of thing.
The outer bearing race needs to have a round hole in the middle. I couldn't cut that with the bandsaw, and didn't want to cut the 18 mm Baltic birch plywood on the scroll saw, so I used a drill press circle cutter.
I cut from both sides. Before finishing the cut on the second side, I clamped the workpiece to the drill press table because, once the circle cutter breaks through, the stock has a tendency to jump around if it's not clamped down.
Then I roughly cut the outside on the bandsaw.
The outer ring is made of two layers of Baltic birch. I cut them out before gluing them because the circle cutter isn't very good at cutting deep holes. First I clamped them with weights, but once the glue partly set, I switched to clamps. If I clamped it right away, the glue (being a lubricant) would cause the joint to slide out of alignment.
I also added a 8 mm thick sacrificial layer on the bottom. This layer has a hole in the middle, which allowed me to line it up with the faceplate of my homemade lathe. I first clamped the workpiece to the faceplate...
...then put the faceplate on the bench, drilled pilot holes, and screwed the workpiece to the faceplate.
I then mounted the faceplate and drive shaft to the lathe, attached the top half of the wooden bearing blocks, and gave each a drop of oil. Adequate lubrication is important with wooden bearings.
I then used a scraper to enlarge the hole slightly, thereby ensuring the hole was centered on the lathe.
I used a gouge (but using it more as a scraper) to cut a groove on the inside for the marbles to run in.
After that, I turned the outside round, ensuring it's concentric with the hole in the middle.
It would have been tempting to use a parting tool to cut it off the sacrificial piece, but I would have hit the screws I used to attach it (this might have worked if the sacrificial piece was much thicker)
So instead, I unscrewed it and cut off most of the overhang of the sacrificial piece on the bandsaw.
I then put the piece on my small table saw sled, with a block on the right to ensure I put it in proper alignment, and cut the sacrificial piece off one part at a time. Doing this sort of operation without a sled would be very dangerous. With a table saw sled, it's only a little bit dangerous.
Then cleaning up the cut on my homemade belt sander. I use the sander for quick operations between other steps quite often, so having the sander with it's own dust collector helps a lot - not having to worry about opening blast gates or turning on a separate dust collector.
Placing two marbles in the groove, plus a piece of scrap underneath to keep them from falling out, I measure the distance between them. This tells me how big the center part of the bearing should be.
The scraps from cutting the holes for the outside rings were big enough for the hub. Here I'm drilling the central shaft hole.
The best way to mount that central piece on my homemade lathe was to just make a mandrel on the lathe, then ram the workpiece onto that.
Then turning the outside cylindrical, with a diameter about 1 cm greater than what I measued between the marbles earlier. The depth of the groove will be to what I measured.
Here comes the clever bit: By moving the hub off to the side, half the groove can be filled with marbles.
Then, with the marbles spread around the circumference, the hub is locked in place. But there needs to be something that keeps the balls evenly spread around so they don't bunch up on one side.
In normal ball bearings, which are assembled the same way,
there is a ball cage that does this job. I cut open a small cheap
roller skate ball bearings to show.
I cut some thin wooden rings out of 12 mm Baltic birch plywood to make a ball cage out of wood.
I fully cut the inside holes of these rings with the circle cutter as well as most of the outside, but finished the outside cut on the bandsaw. It would have been too risky to fully cut the outside of the rings with the circle cutter as well. The ring would probably have gotten loose and smashed by the circle cutter.
I then needed to drill some holes just larger than the marbles But with a drill this large in a workpiece this thin, I was pretty sure the drill would tear it up unless it was very well secured and clamped together.
So I made a jig to fully support the ring on the bottom and squeeze it from both sides while drilling.
This worked out fairly well. I only broke the wood in one place.
My initial intent was to screw the two halves of the ring together, but even #4 wood screws would have been too big. So I drilled some holes through both pieces and snaked some copper wire back and forth to hold them together.
The ring worked, but it obstructed the view to the marbles and also added a little bit of friction.
With the main purpose of the bearing being to look cool, I opted for a different solution.
I screwed together two pieces of birch plywood, drilled the hole, and turned it on the lathe to make a new hub that could be split apart for installation.
This way, I could fill the entire bearing with marbles.
There is friction between the marbles, so this version stays spinning for less time than the one with the ball cage. But more importantly, it looks much cooler.
This bearing was just for fun, but using marbles to make a lazy-Susan style bearing is much simpler. For example, see Peter Collin's sit-and-spin toy using marbles to make a bearing.