Having experienced your exact problem, and not possessing the "plywood" sized
router bits, I've been very happy with the router jig
http://www.rockler.com/ecom7/product...rings_id=10482 -
manufactured by Accurate Woodworking Tools http://www.accuratewoodtools.com/. It
automatically sizes the dados to the exact thickness of the plywood (or other
stock) that you have, using a standard 1/4" or 1/2" router bit.

No connection to either company, just a satisfied woodworker.
--
JeffB
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