Tod Raines gave a wonderful demo on how to create a Bowl in a Bowl. He used a Cedar Elm bowl blank for the demo project. Some of the tips he mentioned include

1. Make sure the outside is a true spherical surface. This will help in getting a nice seating in a concave spherical jam chuck. If it is a little flat or out of shape then there will be gaps between the jam chuck rim and the outside surface of the bowl.

2. Make some templates out of card board for the shape of the bowl by drawing concentric circles and then making the cutouts. You can use the templates to check against the outside of the bowl to get it to the right shape.

3. Use an iGaging 8" Digital Outside Calipers to measure the thickness of the bowl. He managed to get an even thickness of 0.99" all the way from the rim to the bottom of the bowl.

4. After putting a wooden concave jam chuck on the head stock he used a Rubber Chucky flat bottomed cone chuck on top of the tail stock live center while doing the final turning of the outside of the bowl. The jam chuck along with the rubber chucky in the tailstock helps you rotate the bowl to any position you like since the outside and inside of the bowl are truly spherical.

You can visit his website at woodturningtoolstore.com