"mkr5000" wrote in message
...
I really need to route it because I need to plunge into it and don't
want the slot the total length of the board.

Been a long time since I've done this, so can't remember if I can
route that wide a slot (3/4") -- just 1/4" deep or even less, just
enough to fit another piece of 3/4" plywood into.

Do they even make a 3/4" bit or would I have to do multiple passes for
both the width and depth? (yuk).

thanks

As mentioned, Leon... Oh that's me. I have designed a jig to route a slot
to be exactly the width of any thickness piece of wood that you would want
to fit the dado.

But! If you simply want to do the deed and be done you can use the
principal that my jig uses and be done with it pronto.

What you will need,

1. A "Top Bearing" straight cut pattern bit. I was able to pick up cheap
ones 1/2" in diameter for around $5-6 each a few years ago.
2. Two straight edges the length of the dado you want to cut and preferably
at least 1/2" thick. Plywood works well for this.

What to do.

1. Clamp one straight edge exactly where you want the edge of the dado to
be located.
2. Use a piece of the actual material that is going to fit in the dado and
stand it on edge next to the board you just clamped.
3. Clamp the second straight edge up next to that piece of scrap.
Basically what you end up with are two straight edges defining exactly where
the dado will be and exactly the width of the material that will fit in the
dado.
4. Remove the scrap material.
5. With the top bearing bit in your router plunge down between the straight
edges until the bearing is below the top surface of the straight edge. Use
both straight edges to guide your cut. The top bearing will ride along the
inside edges of the straight edges. You will have to make a couple passes
but do not move the straight edges until the dado is complete. When
finished the scrap should fit perfectly into the dado.