I would assume that the additional resistance of a finger is fairly negligible compared to the density of hardwood or metal
In: Engineering
[removed]
Seeing a lot of not quites in this thread. My freshman year of electrical engineering degree that I never finished, the guy who invented saw stop came and demoed his saw and gave an explanation of how it works. It’s not about current.
The cartridge monitors the capacitance of the blade. When the capacitance of the blade (and whatever its touching with relatively low resistance) drastically rises, it triggers the brake. When you touch the blade, the cartridge sees more capacitance and triggers. This is why wet wood or wood with nails can trigger it. The wet wood can hold charge much better than dry wood, so it is able
[removed]
Contrary to most answers here. Devices like SawStop use captive sensing not resistive.
Simply touching the blade does not make you part of any circuit. Doing so would also be a safety risk since any malfunction of the device could send more current down your body than is safe.
Instead they use captive sensing. The circuit monitors the capacitance of the blade and when something with high capacitance is added to the blade it can be detected without any significant current passing. The blade has a known capacitance that is tested when powered up. If that changes say more than 10%, fire the safety mechanism. [Here is a tutorial if you are curious.](https://playground.arduino.cc/Main/CapacitiveSensor/)
[removed]
It is based on the capacitance of the finger. The technology is quite similar to modern touch screen technology which is only able to detect fingers but not gloves. Wood is usually too dry for the sensors to trigger and the metal is too small for it to trigger. This is of course something the designers have to take into consideration. Possibly the hardest thing you can put in them is soaking wet wood for example if you are sawing raw lumber out in the rain but they have apparently been able to set the sensors to handle this as well. However as the SawStop patent is about to expire and competing products have already been shown to the market as being much cheaper to trigger there might be some advantage to triggering on metal as well protecting the blade.
The saw blade carries an electrical current, and the braking system monitors this.
When your hand touches the blade, your *electrical* resistance changes that circuit and triggers the emergency stop.
The stops are quite violent, so don’t test this.
There’s an electric current running through them. Your body conducts electricity, wood kinda doesn’t. As soon as it makes contact with you, the electric signal pulls the blade away. As fast as electricity can react, which is why in the ads you see people will barely have a scratch on them
Latest Answers