This is a blade shaper. To make it set Table saw blade at 10 degrees and rip a 8" 1 X 2 glue sandpaper on both sides and screw on to a piece of plywood long enough to clamp to a stable surface. My Table saw in this case. Use the coarsest you can find to start.show here is piece of 36 g for a beltsander. Put the blade in the groove and put it towards you while gently pushing the blade down. When you have less than 1mm of edge to taper switch to 80 grit in a hand sander and finish shaping. Finish with small pieces of 220.
The third photo is the finished blade.
There is a point to note; My blades are 4mm. (5/32") wide, if you use a thicker blade you may have to change the design to fit.