We know that the SawStop has an awesome safety feature that stops the blade if it detects flesh, but how does that safety feature actually work?
The key factor in the SawStop’s detection system is an electrical signal that the saw puts through your metal blade. The SawStop watches this signal like a hyper-caffeinated hawk, looking for any changes. Because the human body is conductive and can hold an electrical charge, the electrical signal easily passes to the SawStop’s operator if his or her flesh contacts the blade. This produces a change in the signal, and the SawStop reacts immediately.
In the brake cartridge is a block of aluminum (known as a brake pawl) on top of a spring, and the spring is constrained by a fuse wire. The SawStop burns the fuse wire with a burst of electricity to release the spring, which then forces the brake pawl into the teeth of the blade. As the blade digs its teeth into the brake pawl, its own momentum causes it to retract beneath the surface of the table and the power to the motor is shut off. All of this happens in a very tiny fraction of a second with the slightest contact, as you can see in demonstration videos.
The SawStop detection system’s dependence on its electrical signal is the reason that it is important to use conductive metal blades without coated tips. If the signal cannot get to your flesh, the SawStop can’t detect you and therefore can’t activate the brake cartridge. Additionally, because it is using an electrical signal that relies on conductivity to determine that it has contacted flesh, the SawStop will also trigger if you attempt to cut conductive materials like aluminum. Materials like plastics, laminates and wood are non-conductive and should not trigger the brake, but if you believe that something you want to cut may cause a false activation, it is a good idea to temporarily override the safety features, do some cutting and then consult the lights on the saw to determine if the brake would have fired.
So that’s how the SawStop safety feature works! After you watch some videos of the SawStop in action (look here and here), I think you will agree that it is a tremendous feat of engineering.
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