On Thu, 6 Dec 2012 14:10:25 -0800 (PST), "
wrote:

On Dec 6, 11:41*am, "Michael A. Terrell"
wrote:
" wrote:

On Dec 5, 2:50 pm, "Michael A. Terrell"
wrote:
" wrote:

You do realize that turning off the saw via the switch is
very different from a power failure, right? *Using the
switch there is still power available to the protection
circuitry. *During a power failure there is not.

* *A relay with it's coil across the power line when the switch is on
will stop it, if the power fails. *Or configure it with the common
on/off power buttons as a simple motor controller.

It will stop it in 1 ms? * Or at least close enough to instantly
to avoid injury, eh? * You sure about that? *You should go tell
the SawStop guy what a simple, practical new invention you
have. * I say, it just doesn't work.

* *No one claimed that it did, and you just want to whine.


Excuse me, but try to follow the thread. The discussion was
about the SawStop and what happens if power is lost. The
claim was made that it still would work. Then someone claimed
that you could just short the motor and use electromagnetic
braking in case of power loss. The SawStop halts the saw in
1 ms. Something on that order is what is requred to avoid
an injury like you see in the video, where a finger is stuck in
the saw. Ergo, if electromagnetic braking can't stop the saw
in a similar time, it's worthless. And I say absent some
large external power source, it can't.

Different issues. It's doubtful that you want to trigger the SawStop
device just because you lost power. It is *probable* that you want to
shut down the saw quickly on power loss. The fault isn't the same nor
is the timing requirement.

The third issue is just the normal spin-down of the blade. The only
time I've ever come close to making contact (actually have, on it's
side) is when it's spinning down. There is no noise and you can't see
the teeth so it looks like it's stopped. It would be *very* helpful
to have dynamic braking on the blade (and no, I don't want to trigger
a SawStop event every time I turn off the saw). The cost is next to
nothing and *is* done on miter saws.




* *It is useful to stop the blade faster when the power is turned off,
or with a few more parts, when the power fails.

No **** sherlock. You really think so? But that wasn't the
specific issue, though was it? The issue was whether the
SawStop works when there is a power failure, while the saw
is spinning down.

Actually, it was.