Ralph, the problem that you have here is that with the curve running diagonal to the main bowl, there will always be a place where the tool runs from wood into air. At that very point, even with a perfectly sharp tool, the wood fibers will have a tendency to bend rather than being cut, because they are unsupported. And that's when you end up with those feathery bits hanging off the edge, or worse (mostly in end grain) being ripped off. You have both.
I can only see several ways out of this:
- follow Pete's recommendation (although this would result in other difficulties, because the turning axis is now offset from the main bowl axis, and therefore you end up with varying wall thicknesses).
- turn the outside bowl finished (possibly including sanding) before cutting it and fitting it to the inside bowl.
- don't cut the curved groove until right at the end. You could achieve this in two ways:
- Only glue the two bowls together with hotglue, which can then be softened, so that you can remove the outside bowl for the cut or
- glue them together for good, and use carving tools for the groove.
In any case, this is a challenging project. Good luck with it.
Remember, if you don't push boundaries (and yourself), you just stand still. The cost of this is that sometimes it doesn't work the way you first thought, and you may have to start again. I am pretty sure that once you succeed, you will have a rather marvellous piece.
