"eganders" wrote:

I need to make a spiral groove in a couple of columns. I only have
to
do it in two columns and I may not do another for a LONG time, so a
complex jig that will take room and time to build is not an
attractive
approach.

Find somebody with a Sears & Roebuck "Router Crafter".

It was an accessory for a router to do specifically what you want to
do.

Lew