If you already have a sled, it is easy. Just put on a dado blade the width that you want the fingers to be, then set the height the thickness of the material. I like to then take a piece of 3/4″ MDF about 2 feet wide by about 5″ high for a sub back fence to be clamped to the sled.
Make one cut near the middle of one of the long sides, then make a key or index pin that perfectly fits into this slot, and sticks out about an inch to the front side. I normally glue and staple it in the slot, then with a chisel cut a bevel on the top half of the pin which makes it easier and faster to find the slot between cuts when it tapers up.
You then clamp this to the fence of the sled with the pin offset by the thickness of the cut. Then make a sample cut on some scrap to check the fit. It normally takes a couple of tries to get it just right by loosening the clamps and tapping to one side or the other.
One last tip. If there is any slop between the sled rails and the saw-table slots, you need to make sure to have a little pressure to the same side each and EVERY cut. If you only have say .0010″ of play which is pretty good, but feed one board while pushing this tolerance to the right, the feed the next while leaning left, they will not fit even if nothing else has changed.
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Keith's advice is very good. I have made a box joint jig like he describes and it worked fine BUT I had to do alot of "fussing" to get the index pin and spacing correct. Any errors get multiplied as cutting continues across the worpiece. I have since purchased the first generation very inexpensive INCRA jig and use it to index the box fingers. It really is more accurate. Any commercial indexing jig system will work. I now do the box joints on the router table with spiral upcut bit and cut thru the workpiece and into a scrap backer to control chipout. This results in clean cuts on all edges of the individual fingers. I set the bit for 1/64" higher so the assembled joints can be sanded flush after glue up.
Don
I have not tried a router table jig, as of yet.
It sure can't be any more frustrateing? Thanks ah million.
Thanks so much for the imput. Will try agine.
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