Built in 2014 to functionally emulate the Kerfmaker by Bridge City Tool Works. The original tool is brilliant, and allows one to quickly make perfect dado cuts on a tablesaw, but is expensive and seemingly never in-stock.
For simplicity, here's how it could work for cutting a rabbet (dado on the edge of a board):
Set the tool to the desired rabbet width. To do this, loosen the brass nut, slide the tool open, place a piece of material of the desired dado thickness between the aluminum end-plate and top-slide, slide the tool closed around it, and tighten the brass nut.
Clamp a stop-block (here I'm using a finger for demonstration) to the crosscut-sled fence so that the aluminum plate is aligned with the edge of the blade. Place material to be cut against the crosscut-sled fence and aluminum plate of the tool, and make the first cut. Note: never actually do this. The blade will probably catch the aluminum plate of the tool, and send it flying. At the very least, you may severely injure yourself.
After the first cut, flip the tool and slide it back against the clamped stop-block, offsetting the second cut so that the distance between the outside of each cut perfectly matches that between the aluminum plate and the sliding portion of the tool, where the template was initially clamped.
Between the two original cuts, make multiple cuts to remove all material between them. If any material remains, it may be cleaned-up with a chisel.
Note: To make a dado, offset the tool father from the blade by clamping the stop-block farther down the fence, as much as is necessary to properly space your cut from the edge of your board.
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