Well I just got my copy of De Cristoforo's book and while it is
certainly a great addition to my collection of information on tools and
jigs, the rotajig which is described in this book isn't exactly what I
was hoping to find information on. You could conceptually use this jig
to create a spiral on square or round stock, but the accuracy would be
determined by how well you can manually control the rotation of you
stock. From what my wife's uncle described to me the jig his son had
(or maybe has?) had some sort of gear-driven mechanism that would
accurately control the rotation of the stock over the tablesaw blade
while doing a coping cut. I'll have to see if I can contact his son...
Thanks though for turning me onto this book. I'm glad to have it!