Lathe spindle bearing help

[Ed Weldon]

Don't consider needle bearings for a lathe spindle. They have plenty of load capability in sizes to fit a small lathe spindle. But you can't easily adjust the internal clearances as you can with preloaded ball bearings and tapered rollers. And needle bearings don't like high speeds. Also they can't handle thrust loads like from cutting tool loading; so you will need to fit a separate thrust bearing for both axial directions. I recommend repairing the existing bronze bearing setup.
If you must convert then go with ball bearings of outside diamteter that can be easily fitted to the existing headstock casting and machine a new smaller diameter shaft. The trickiest part of this will be fitting a special sleeve needed to adapt your current stock of chucks, faceplates, etc and likely require you to find other uses for your collets. This all will require a compromise in how you use the lathe. Specifically go easy on loading your cutting tools, expecially on interrupted cuts.
If you are an ameteur like me you already do mostly light cuts anyway. I've always been a half assed hobby machinist. But my work was mechanical engineering and my specialty for a few years was high speed centrifuge drives. The kind that were in the same class as the ones used to separate uranium oxide gas into stuff used to build bombs. But that's another story.