Okay, forgive my choice of "teenage" language, but in this case it's
accurate. I have been thinking and googling for weeks about how to
mount a simple extension table on the standard length fence rails on my
Grizzly contractor saw, and when the obvious solution finally worked
it's way into my brain, I felt stupid for taking so long to think of
it.

First, my needs are simple, and I plan to use the table saw fence (with
t-slotted sacrificial material)for routing, so I didn't need to add a
large extension.

Second, I need to get up and routing quickly for one specific project
so I don't want to take the time and effort to make the ultimate router
table. Legs, hinges, leveling etc. are not all that difficult, but add
a lot of time to the build. I'll probably end up using this first table
to make its more elegant replacement.

Try as I might, I couldn't think of an easy way to get the table
attached to the rails for a solid and level fit. Since I accepted the
fact that this first table would most likely be modified/improved in
the future, I wasn't fond of the idea of drilling holes in the rails,
not to mention the headache of removing them and wrestling them onto
the drill press. Plus, mounting any hardware on the rails has to be
done strategically to avoid interfering with the fence. Finally, the
front and rear rails each present different problems with clearance,
shape, and level.

I had pretty much given up and decided to go get Rockler's $109 (no
insert) table to clamp into my Workmate. On the way to the car, I
stopped at the table saw to give myself one more chance to avoid
admitting defeat and burning the cash, and it came to me!

Setting a piece of 3/4" MDF shelving across the rails, I saw that the
MDF was about 1/10" proud of the table surface. (The top edges of both
rails are the same height relative to the surface, and the rail stock
is 1/4" thick). I cut one piece of the MDF to slip exactly between the
front and rear fence rails, and cut a second piece 1/2" longer to rest
on top of the rails (1/4" on each end). Next I routed a 1/10" deep
rabbet on the edges of the longer (top) piece to bring the surface down
to match the table height. Laminated together,with the top piece
overhanging the bottom, The assembly slips perfectly between the rails
with the top resting comfortable on the edge. It can them be held to
the lip of the tabletop with bar clamps placed underneath.

Before "laminating" the two pieces, I cut the hole in the bottom piece
and mortised the top piece underneath to accomodate the router.
Finally, I made the dado for the store-bought t-track channel and I'm
done. I bought an insert, but for this first attempt, I'm just going to
mount the router directly in the table.

The extension is only 11" wide, so I'm limited in the width of stock
that can be edge routed with the fence on the left, and the feed
direction will be from the rear of the saw. You can't go much wider
because the rails don't extend that far. For larger pieces I'll have to
change the fence over, move it to the right, and feed from the front.
My upcoming project will not require that.

The whole job took about 2 hours, and that included teaching myself how
to use a router, and several practice passes. Most of you folks could
do this in a half hour, including the routing for the insert, which I
skipped. In the next version and add the insert and make the top out of
Melamine. By then I'll probably have a better idea of the perfect
location for the t-tack as well.

This or a slight variation will probably work on most fence systems. If
you've been thinking about adding a router extension to your table saw,
this is a great start, and it's so easy that you won't mind if you want
to remake a nicer one in a few months to add features.

Tom