Having come back to rebuilding after an absence of a number of years, I'm delighted to be learning new techniques.

In the past I was frustrated with the hand filing of notches on key tops. I found a jig documented in an old Journal article by Bill Spurlock and put one together. It was well worth the time! Here's the details:

A jig for notching keytops

I suppose that will work until you come across a piano where the sharps are not even across the front, like one of my Mason & Hamlins.

You're stretching my experience here. So what you are saying is that the front of the sharp is not parallel with the key slip?

The fronts of the sharps are not parallel with the key slip. If you put a straightedge against them, some are closer to the keyslip than others.

OK. I think you're saying that they are parallel, but not equidistant from the keyslip.

Sounds like a manufacturing defect to me. In rebuilding, I think I'd want to adjust the placement of the center pin or center pin bore in the key.

Any thoughts?

Life is too short to waste one's time on things like that.