SawStop is a table saw manufacturer headquartered in Tualatin, Oregon, US. The company was founded in 1999 to sell table saws that feature a patented automatic braking system that stops the saw within milliseconds if its blade comes in contact with the operator's hand or other body part.Table saws are the most dangerous woodworking tool. In the united States, 10 finger amputations by table saws occur every day. The operator holds the wood, rather than the saw, making it easy to guide fingers into the saw, while guiding the wood.How it worksSawStop's saws apply a small amount of electric voltage to the blade of the saw. The current through the blade is continuously monitored. If the saw detects a change in this current (as would occur if a hand or other body part came into contact with the blade), an automatic braking system is activated, forcing an aluminum brake block into the blade. This aluminum block is designed to absorb the energy of blade by deforming.According to the manufacturer, the saw stops in less than five milliseconds, and angular momentum retracts the blade into the table. The operator suffers a small nick instead of an amputation or other more serious injury. The design takes advantage of the difference in "electrical conductivity" (similar to a GFI circuit) between wood and flesh.The SawStop Jobsaw's 10-inch blade turns at 4000 rotations per minute (RPM). This means the circumference moves at 3.1416 x 10 x 4000 / 60 inches per second (ips), or 2094 ips. Therefore the blade normally moves at 2.093 inches per millisecond.Contact detection subsystemThe SawStop saw was designed to reliably detect flesh contact, with few false alarms. An oscillator generates a 12-volt, 200-kilohertz (khz) pulsed electrical signal, which is applied to a small plate one one side of the blade. The signal is transferred to the blade by capacitive coupling. A plate on the other side of the blade picks up the signal and sends it to a threshold detector. If a human contacts the blade, the signal will fall below the threshold. After signal loss for 25 micro seconds (µs), the detector will fire.
