Quote Originally Posted by Joe Scharle View Post
Make an adjustable dado jig and forget the special, undersized bits. This one has a built-in clamp, but yours wont have to be as complicated.

I agree with the jig. You use the ply in question to set the width of the dado. Nice fit every time. I made my jig with 3/4" sides and use a 1/2" pattern bit. Clamp one jaw, insert a piece of the subject plywood, set the other jaw snug and remove the plywood sample. Run the bearing against each jaw and perfect fit, no having to calculate bushing offsets. Downside is that it only works for 1/2" and wider dados.