My instructor for this project suggested that I use spacer blocks to cut the second shoulder for the tenons to fit the mortises needed for this rocking chair. I was about to make those spacers when I received a new issue of Woodcraft Magazine. The article in the Feb/Mar 2016 issue was entitled Twin-Blade Joinery. With this method I would use twin RIP saw blades with disks or shims between the blades. With the right combination of shims I could cut tenons for the following mortise sizes cut with my Powermatic mortiser and hollow mortise chisels: 1/4, 5/16, 3/8, and 1/2 inches.
These are the aluminum disks I made and will use with the existing 8” Diablo DADO set I own. I had already cut sample mortises in a block of wood: 1/4”, 5/16”, 3/8”, and 1/2”. I will later determine the shims needed to fit a tenon to a 5/8 inch mortise.
I labeled all the shims including those from the Diablo DADO set. From the combinations needed for these mortise sizes I have written a log to record the shim combinations for each of the mortise sizes.
I believe this will speed up my tenon cutting and mortise fitting process…
-- --- Happy Howie