On Jan 18, 2:44*pm, Pat Barber wrote:
Don't try to get to the thickness of the plywood.

Cut a rabbet to a "known" thickness(1/2" is good)
and then route a slot using a 1/2" bit.

Using this method, you can really get very close
and not worry about weird sized plywood.

Actually, I would make my dado and sneak up with
the rabbet.

You can do this with a table saw or a router table.

I've used that method when I've pre-finished the components. The
rabits and dados then expose unfinished wood for the glue to bond to.