Saturday, December 8, 2007

Repairing the bull gear and cone pulley

Probably due to the previous 'fix' to the lathe, there is a considerable amount of wear on the hubs of the bull gear and cone pulley. As far as I can tell, there was no bearing between these parts. They were pressed hard together by the force of the spindle and frequently spun at different speeds. The Zamac hubs rubbed and eroded themselves down. Eventually, the outer edges of these parts started rubbing together and caused scoring. A bronze bushing in the cone pulley stopped the damage to that part, but the bull gear kept getting chewed up, if at a slower rate.

I decided to make room for a bearing between the bullgear and cone pulley. I'd size it so the edges ended up close but wouldn't touch.

The bull gear's right hub has seem some mysterious wear. I don't know what caused it. It was unsightly so I removed it. It also prepares for a possible retainer bearing similar to the one I put by the change gear. In addition, there are 60 holes at the edge of the bull gear for indexing. As is all too common, the retaining pin got pushed in while the lathe was running and tore up the holes. I smoothed the hub and indexing holes.

I turned the bull gear over and took about 90 mils off the the hub area. Note the damage to the edge of the piece - this isn't machined. That's where it wore against the cone pulley.

I turned my attention to the cone pulley. It's hub was not nearly as damaged due to the protection offered by the bronze bushing. I ran over it with Marco's mill. Again, note the damage towards the edge. That's where it rubbed against the bull gear.

This picture shows the bull gear with the sintered bronze 'oilite' bearing in place. The bearing is proud of the surface to prevent the wear around the edges of the parts.

Here is it all together. The cone pulley and bull gear are protected from one another by the bearing. Since the bearing is thicker than the amount of material I removed, the edges of the parts no longer touch, as seen in the following picture.

I need to file a few flats in my spindle for set screws. But otherwise this completes the headstock repairs.

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