For lathe spindle bearings, i know it's common to use two angular contact bearings on the far left, and a plain bronze taper bearing on the right. I was thinking about spreading the angular contact bearings apart to both ends of the headstock (while keeping a back-to-back arrangement and preload) and eliminating the bronze bearing. Is there any obvious reason why this would be problematic or inaccurate?

Bearings: ABEC 1 with 40 degree contact angle


For the spindle, i'm thinking about making it out of mild 1080 steel. If a plain bronze taper bearing is used, is 1080 steel compatible in terms of wear with the bronze bearing. Does anyone know what spindles are typically made out of (hardened and ground steel?)?

This isn't going to really help your situation, but some of the highest quality spindles are made of high-nickel alloys. Very low thermal expansion, and tremendous wear capacity. They are nitrided at low temperatures (for hardness), then slowly stabilized.

These spindles are incredibly stable over a very, very long period of time, and they really limit the effects of thermal instability.