Reply by tblank

When I have several chairs (or two) that have to match, I draw the outline and make a series of concentric lines 1” apart. Then from actual center of seat, draw lines radially (about eight, give or take) and then chuck a 1/2” bit into the drill and set the depth at all intersecting points. I just use a stop collar for the varying depths. From there it’s a matter of grinding away to blend the bottoms. Keep in mind the ridge line in the center. The depths can be worked out ahead of time from a pattern.