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Other people who have added modern bearings to their wooden treadle lathes report the bearings eventually moving around and becoming wobbly.
The solution is housing the bearing in something harder than the typical softwood we use for the lathe frames. Let’s see now… oak, ash, … ah, there’s some walnut left from a gun stock project. There’s enough walnut for the bearing blocks and for a few other small parts. Perfect.
There are a total of 4 bearings, two 1/2″ for the flywheel and two 5/8″ for the headstock. One of the 5/8″ bearings is a thrust bearing that will absorb the headstock’s lateral movement. They have outside diameters of 1 and 1/8″ and 1 and 3/8″. Forstner bits in a hand brace do the job. I drilled several holes through a block that’s a bit more than twice as thick as the bearings. Then, I sliced the block into the correct thickness. It’s a simple resawing task, but the work pieces were too small to handle well for manual resawing. So, I relented to using the band saw. After that, saw to size with a Japanese pull saw. Yes, I’m leaving them square. It’s easier than making them round.
By the way, I can’t say enough good things about my Czeck Edge marking knife. It’s really hard to mark dark woods for sawing. Pencil lines disappear. Pen lines are too fat. The marking knife makes perfect lines that are both precise and very visible.
P.S. I’ll be remaking the block for the thrust bearing. I’ve decided to double up on that one by placing the thrust bearing and a regular bearing sandwiched together. It’s a simple matter of more boring boring.