Hi Bill,
I can't but say you've tackled one very difficult piece, heavily spalted, no doubt more than soft in places and half the rim missing.. Oh and Birch too .. tooling and sanding wouldn't have been easy, as is apparent, not easy to pick up the cut on the rim or with sanding the piece, but you've done a blxxxy good job, the outer form has a lovely flow, and you look to have gone for the same inside, did you fear in having gone too deep and hence created a slight corner to the base, depending on the timber you could have done with a bit thinner and a detail with the chuck mount just to hide it, then that's just how turners' judge it ... Excellent what you've done, one to keep and look back on.
Cheers David