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Here is how to easily modify your existing steel rip fence to make easier rabbet cuts with your dado blades. The dado blade sits underneath the slot in the wooden fence, allowing you to make easier rabbet cuts.
You will need:
A 2x4 or there around piece of lumber
3 or 4 bolts, I used three 1/4" wide, 2" long bolts with 3 washers, nuts and lock washers
A table saw
2 C-clamps
A small, pointed object
Drill press or hand drill with appropriate bits, I used a 1/4" inch bit and a 3/4" bit
Step 1Examine your rip fence
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My rip fence came with 3 pre-drilled 1/4" holes in it. If your rip fence does not have pre-drilled holes in it, you can safely drill 3 or 4 1/4" holes in it without compensating its integrity. To do this, measure out 3 or 4 holes on your rip fence. If your saw blade is in the middle or near the middle of the rip fence, measure out 4 holes. If the blade is closer to the back of the rip fence, 3 holes is enough. MAKE SURE that you do not put the holes in the area where the blade cuts, keep the holes at least an inch or two from the blade area.
http://www.grip-tite.com/GT1/HoleClamp.html
With those, you just drill a couple of vertical holes in the sub fence and clamp on.