The tool that you are talking about is a 'Marrison System ' sold in
the UK by
Craft Supplies UK. It is a grooved jig used with a parting tool and
will enable you to cut rings from a flat board at a 62 1/2 degree
angle and will produce rings up to 12" dia. When stacked and glued the
rings will form the shape of your bowl for final turning.They claim
that using this system, you will reduce timber wastage from 80 to less
than 5 per cent.

Jack.