Chas, always a little movement but using end grain at least the rim won't cup. I prepped the pewter ring and then trued the laburnum rim and tongue just prior to epoxying the ring. I was trying to leave the bowl wall pretty thick to balance with the weight of the metal, about a 1/4 ". It's certainly a challenge to cut a thick green bowl with the pith included. The pewter's strong enough to not distort; the only danger is it adding tension to the wood as it dries. The growth rings in the laburnum were quite concentric which helps.
Hope that helps, drop me a comment on the blog if you have more questions.
Thanks, Bill