Stuart:
I manufacture a reasonably priced laser guided tool for hollowing. The
advantages of the laser are the ability to know where you are cutting without
stopping every couple of minutes to measure. Additionally since the tool is
constrained by the holder wrist and arm strain are eliminated as is the back
strain associated with bending down to see inside the work as you are
hollowing. if you're interested you can check it out at:
http://www.rizomausa.com/brtools
I can email you a user's manual if you'd like.
Brian Rosencrantz