Arch
I am not sure how I would drill the holes, but I would generally not bother
so I am not much help. On the other hand I usually rough turn between
centers, including the hollowing. For the final turning I use a glue block
and finish turn from one fitting. It just seems easier to me and I do not
have to worry about concentricity when remounting.

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God bless and safe turning
Darrell Feltmate
Truro, NS Canada
www.aroundthewoods.com