Oops - I made the classic RCM mistake: I didn't give the full picture and the thread got out of focus. The full picture is this: I got half a lathe at the dump and I'm parting it out. Most of the parts are in really good shape, but the bed has this rust that I'm talking about. My real question is this: if I remove the rust and don't do anything else, will the bed still be useful? I.e., will it be worth putting on eBay (with full disclosure)?
So I don't intend to sand it. The sanding in the picture was to give an idea of how severe the rust was, by comparing it to the scratches left by the 100 grit paper. And the sanding was done to the side, where the carriage does NOT bear on the ways. Likewise, the stoning in the picture was only done to try and highlight the rust pits with some polishing. (Stone off the "peaks" so the "valleys" will show by contrast.)
But I've thinking (!). The bearing surfaces on the carriage/saddle are
9 1/2" long! This means that there will be a considerable bridging effect as it slides on the ways. I'm very skeptical that this kind of rust could have any measurable effect on the lathe's accuracy. But what do I know, so I'm asking.
Thanks to all repliers, Bob