My fingers typically are not very conductive due to old thick skin, and 
exposure to various solvents. I have measured the resistance fingers to 
fingers on opposite sides recently, and it is very close to infinity. I 
don't think I would want to trust it working. The stop is by jabbing a 
piece of aluminum into the blade. There are parts including the blade to 
be replaced after an event that as I understand, are not cheap. I still 
have all my finger tips after 60+ years of use of similar equipment, 
thanks to "Safety is Job ONE". Though at age 7, I was cutting stake 
points on the circular saw that I still have today. One of the fall off 
wedges hooked the back of the blade and threw it into my eye glasses. At 
that time glasses were not the shatterproof, and the doctor had to pick 
glass pieces out of my eye.

On 7/10/2010 6:33 AM, RussellMc wrote:
> Recommended viewing - even if you never use a table or other power saw.
>
> Auto stop saw protection - blade is stopped in about 1 millisecond
> after contact with a conductive object - typically a finger.
>
> I've seen videos of this before but this is by far the best.
> Shown it in action with a sausage and then in fast and slow motion
> from various views with a real finger - attached to its inventor. He
> said it tickled.
>
> Also show the mechanism in action in slow motion so you can see how it
> stops, how fast, what happens to the blade and the energy and more.
>
>              http://www.youtube.com/watch_popup?v=E3mzhvMgrLE&NR=1
>
> Approach speed doesn't want to be "too fast".
> If stopping time is say 1 ms then a 1 m/s feed rate - probably at the
> upper likely end of the speed range, would result in ~= 1 mm
> penetration into the cutting zone after 1st contact. At say 1200 RPM =
> 20 rps a blade will rotate 20/1000 = 1/50th of a turn or about 7
> degrees in 1/1000 second. Scale up for faster RPM. Blades have from
> about 20 teeth up or from about 18 degrees per tooth or less, So
> stopping COULD be under 1 tooth time but may be several teeth and
> perhaps several mm into the "target" worst case (fast feed, fast
> blade, many teeth). So you'd expect you MAY get a nasty nick worst
> case, as long as the system works OK.
>
> Blade and brake die at each actuation so you don't want to try this too often.
>
>
>                 Russell
>
>
>
>
>
>
>                       Russell McMahon
>
>
> __________________________
>
> Reference from Iona.
>    
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