Macroware Technology
Saw Stop Table Saw Safety Device
posted Friday, 22 September 2006
I saw an article in Design News magazine this month about a device that improves the safety of table saws [1]. I have a table saw, and have always been extremely careful in using it because of the safety hazards. I consider it by far the least safe tool I own. The new safety device was designed by Stephen Gass. The article describes the design of the safety device as well as the extreme resistance of the power tool industry to this invention. The resistance is based mainly in the fact that tool companies think that adding such a safety device would mean that they are admitting that their existing devices are not safe and open them up to law suits. They also argue that cost is an issue. It's interesting how the litigiousness of our society is actually preventing the widespread adoption of a great safety improvement in this case.
The device works by stopping the table saw blade if it senses skin in contact with the blade. The sensor is a capacitive sensor that uses the saw blade. A small AC signal is applied to the saw blade, and if skin comes in contact with the blade the capacitance of the blade changes and this change can be sensed by a microcontroller very quickly (the micro samples every 6 us). The other design challenge is how to actually stop a blade spinning at 4000 RPMs fast enough to not cut through a finger. Their design brings the blade to a complete stop in 3 ms.
The online verison of the article on the Design News web site has a video clip of the device in action with a hot dog. The blade stops when it touches the hot dog.
Since Gass could not license the patented design to any power tool companies because they refused to use the technology, he started a company called SawStop LLC that makes saws using the technology. They are supposed to come out with a contractor saw soon, and this will be at the top of my tool wish list. Goodbye to my old table saw!
[1] Murray, Charles. September 4, 2006. "Man on a Mission." Design News Magazine Vol 61 Issue 12, pp 54-60.
The device works by stopping the table saw blade if it senses skin in contact with the blade. The sensor is a capacitive sensor that uses the saw blade. A small AC signal is applied to the saw blade, and if skin comes in contact with the blade the capacitance of the blade changes and this change can be sensed by a microcontroller very quickly (the micro samples every 6 us). The other design challenge is how to actually stop a blade spinning at 4000 RPMs fast enough to not cut through a finger. Their design brings the blade to a complete stop in 3 ms.
The online verison of the article on the Design News web site has a video clip of the device in action with a hot dog. The blade stops when it touches the hot dog.
Since Gass could not license the patented design to any power tool companies because they refused to use the technology, he started a company called SawStop LLC that makes saws using the technology. They are supposed to come out with a contractor saw soon, and this will be at the top of my tool wish list. Goodbye to my old table saw!
[1] Murray, Charles. September 4, 2006. "Man on a Mission." Design News Magazine Vol 61 Issue 12, pp 54-60.
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