Table saw that stops when it touches skin

I posted something about the SawStop table saw on Boing Boing a couple of years ago. It has a mechanism that makes the saw blade stop rotating an instant after it comes into contact with human flesh (watch the amazing video of it in action here). Kevin Kelly's Cool Tools has a review of the SawStop from a happy user (who has not had to test out the safety feature yet.)

 Cooltools Archives H00117 01

(A hot dog proxy for a finger gets only a nick when pushed into a turning saw blade) As for the safety features, I've haven't put the brake to the test. Like the air bag in your car, the Sawstop system includes an extensive startup and continuous self test while idle and running. And like your air bag it's very costly to "test." You get only one emergency stop per blade and brake. Besides $70 for a new brake, it's another $50-100 for a new blade. It's pretty high tech. The brake is a special aluminum block and electronic assembly with a fusible (i.e. burnable) wire holding the spring loaded brake block assembly in position. When the electronics "fires" after detecting contact with human flesh, the fusible wire is burned through by a high electric current "pulse". When the wire burns through, the spring loaded aluminum block is shoved into the spinning blade. The blade cuts deeply into the block, and the block absorbs the considerable momentum energy of the blade, arbor, belt and motor. The result is that the blade and block get hot enough near the teeth of the blade to unsolder or weaken the teeth on the blade. In short the blade is ruined 50% of the time according to one web site I found that had tested the unit. Once the emergency brake has been fired you need to replace the whole brake assembly (like the air bag), which includes the brake, spring, retaining fusible wire, firing electronics including capacitor, and brake frame assembly. Replacement only takes a couple of minutes. Despite the cost, it is still better than paying for a new finger. Two friends have lost 2.5 fingers collectively from table saws. And both were experienced woodworkers.

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