When using a four-jaw scroll chuck for wood turning the best hold is achieved when the tenon or recess is matched to the “perfect circle” for that particular chuck. One way to achive this is to make a gage for each of your scroll chucks. I made it at The Tech Shop San Jose,, http:http://www.techshop.ws
/,using the Epilog Laser Engraver to cut my gauges out of ¼” melamine faced MDF.1/4" plywood also works. Do not be tempted to use Plexiglas. If you offer Plexiglas to spinning wood, to check your progress, the Plexiglas will melt. Trust me.