"J. Clarke" wrote in message
...
cg wrote:

As no one offered a little more explanation on how fast
this saw-stop really stops, I would present some simple maths...

From their website they say they can stop a 4000 rpm blade
in less than five (5) milliseconds.
Now, the blade normally takes 60 seconds for 4000 rounds.
In one millisecond, the blade would rotate 1/15 round...
(that is one part of fifteen).

So, if the sawstop mechanism takes 5 milliseconds to stop,
I would expect at most 5 x (1/15) ,that is, one-third of a full
rev of the blade to plough thru before it stops.

Say, I'm ripping with a 24 teeth blade. In 1/3 rev, I would
expect no more than 8 of those teeth to bite me. If I had
been using a 60 teeth cuutoff blade, watch out! 1/3 of 60
is 20!

To be honest, I would reduce the fraction from 1/3 to 1/4 or
1/5 because I have not taken into account the deceleration...
once the brake is applied, the blade is spinning down and it
is not rotating at 4000 RPM during the entire 5 milliseconds.
(So, how long it takes for brake shoes to engage? 1 millisec?)

Even then, for a 24 teeth ripper, 1/5 is 4+ teeth and
for a 60 teeth cutoff, 1/5 is 12 teeth. Little
consolation for me!

I wish the sawstop folks could give out details like
these. In particular, they must already have exact figures for the
rotation before complete stoppage. Instead of telling in terms
of time (like milliseconds) it would be better to state the same
in terms of percentage of a full rev of a 10" standard kerf blade
spinning at 4000 RPM.
Although I must agree there is more truth in their statement
compared to claims like 3.25 HP routers on 115v, or 12" SP/ 1200 cfm
with a 10" impeller 2 HP DC, and the like!

Afterall, they certainly have the brain to see through my simple math...

don't they?

So how many saw teeth have to go through your finger before your finger
comes off?



I don't know it it's so much a matter of the number of teeth as it is how
far into your finger the teeth can get before the blade stops.
--
If at first you don't succeed, you're not cut out for skydiving