On 10/12/2010 5:46 PM, wrote:
On Tue, 12 Oct 2010 11:28:12 -0400,
wrote:


17 teeth?

How fast can you push your finger?



wrote in message
...
That may be true, but they still don't do any harm.



Sawstop stops the blade in 1/200 of a second, according to their Web
site. At 3450 RPM that means the blade stops in .29 revolution, which
with a 60 tooth blade means that 17 teeth have had a shot at your
finger.

Actually significantly LESS than 17 teeth, because the blade is very
quickly slowing down throughout that 1/200 of a second. I believe the
number is something like SEVEN teeth pass the gullet from the time of
contact to full stop, and the last 3 or 4 are pretty well stopped as
they go by.
A demonstation showed a damp peice of cardboard stop the saw with
barely a nick in it.

Another important part of the SawStop design is that the blade is dropped
below the table's surface as the blade is being stopped.

On Oct 10, 10:27*pm, -MIKE- wrote:

"electromagnet/solenoid would do the trick"

My God man, you've invented the Saw Stop!

On Oct 12, 12:21*pm, Steve Turner
wrote:

wildly advancing your fingers towards the blade,

As is done when, say, you are pushing a bit of wood into the saw and
it jerks out of place and you essentially "fall" forward now that the
wood is no longer offering resistance?

Of course, the blade never stop turning at all on the saw I was using,
but I did manage to put three finges and a thumb in its path before
realizing I was cutting skin and bone - and jerked back.

Only cut clean through one digit and got it sewed and screwed back
on.

In article ,
says...

On Mon, 11 Oct 2010 19:59:30 -0400, Bill wrote:

J. Clarke wrote:
In , says...

I would think that an emergency stop mechanism would be a whole different
magnitude than a scheduled, everyday, stop.

For a finger saver an emergency stop mechanism would have to stop the blade
in a few teeth passings. For everyday usage a couple dozen blade rotations
would be OK too. These two situations would require different tactics.

A dynamic electronic brake could vary the intensity for the two different
scenarios and we could add the caliper to the emerg stop. A caliper probably
wouldn't last long in everyday usage and would need to be adjusted and/or
replaced frequently.

So how much power do you have to put into that electronic brake to stop
the blade as fast as Sawstop's physical block?

And why would a caliper not last long? A set of brake pads on a car
with 10" rotors lasts 40,000 miles or so, and they're getting a Hell of
a lot more of a workout that they would stopping a little bitty saw
blade that masses less than 1/1000 as much.

The physics on that seem interesting. A little like stopping a speeding
bullet on a dime--it challenges my imagination. Probably not quite as
difficult as stopping a lightning bolt, but I wouldn't want to try that
either.

Bill
No way a caliper could stop the blade in even 4X the time the
saw-stop does. And keeping dust out of the gap between tha "pad" and
the blade would be quite problematic - with dust decreasing the
stopping efficiency by a very large margin.

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

On 10/12/10 9:12 PM, Hoosierpopi wrote:
On Oct 10, 10:27 pm, wrote:

"electromagnet/solenoid would do the trick"

My God man, you've invented the Saw Stop!


Hardly.
There's a lot more more going on with that thing than a simple current
running through a magnet.


--

-MIKE-

"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com

---remove "DOT" ^^^^ to reply

On 10/12/2010 9:19 PM, Hoosierpopi wrote:
On Oct 12, 12:21 pm, Steve
wrote:

wildly advancing your fingers towards the blade,

As is done when, say, you are pushing a bit of wood into the saw and
it jerks out of place and you essentially "fall" forward now that the
wood is no longer offering resistance?

I've read that about five times and have tried to visualize what you're talking
about, but I'm still puzzled.

Of course, the blade never stop turning at all on the saw I was using,
but I did manage to put three finges and a thumb in its path before
realizing I was cutting skin and bone - and jerked back.

Only cut clean through one digit and got it sewed and screwed back
on.

Would I be correct in assuming you were pushing the wood into the blade with
your bare hands rather than using a push jig or Gripper or something similar?

--
See Nad. See Nad go. Go Nad!
To reply, eat the taco.
http://www.flickr.com/photos/bbqboyee/

J. Clarke wrote:
In ,
says...

On Mon, 11 Oct 2010 19:59:30 -0400, wrote:

J. Clarke wrote:
In , says...

I would think that an emergency stop mechanism would be a whole different
magnitude than a scheduled, everyday, stop.

For a finger saver an emergency stop mechanism would have to stop the blade
in a few teeth passings. For everyday usage a couple dozen blade rotations
would be OK too. These two situations would require different tactics.

A dynamic electronic brake could vary the intensity for the two different
scenarios and we could add the caliper to the emerg stop. A caliper probably
wouldn't last long in everyday usage and would need to be adjusted and/or
replaced frequently.

So how much power do you have to put into that electronic brake to stop
the blade as fast as Sawstop's physical block?

And why would a caliper not last long? A set of brake pads on a car
with 10" rotors lasts 40,000 miles or so, and they're getting a Hell of
a lot more of a workout that they would stopping a little bitty saw
blade that masses less than 1/1000 as much.

The physics on that seem interesting. A little like stopping a speeding
bullet on a dime--it challenges my imagination. Probably not quite as
difficult as stopping a lightning bolt, but I wouldn't want to try that
either.

Bill
No way a caliper could stop the blade in even 4X the time the
saw-stop does. And keeping dust out of the gap between tha "pad" and
the blade would be quite problematic - with dust decreasing the
stopping efficiency by a very large margin.

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.


When it snapped (seriously)? I'm not an engineer, so I don't know for
sure. I just wouldn't be surprised. Maybe someone else can opine.

Bill

In article , says...

J. Clarke wrote:
In ,
says...

On Mon, 11 Oct 2010 19:59:30 -0400, wrote:

J. Clarke wrote:
In , says...

I would think that an emergency stop mechanism would be a whole different
magnitude than a scheduled, everyday, stop.

For a finger saver an emergency stop mechanism would have to stop the blade
in a few teeth passings. For everyday usage a couple dozen blade rotations
would be OK too. These two situations would require different tactics.

A dynamic electronic brake could vary the intensity for the two different
scenarios and we could add the caliper to the emerg stop. A caliper probably
wouldn't last long in everyday usage and would need to be adjusted and/or
replaced frequently.

So how much power do you have to put into that electronic brake to stop
the blade as fast as Sawstop's physical block?

And why would a caliper not last long? A set of brake pads on a car
with 10" rotors lasts 40,000 miles or so, and they're getting a Hell of
a lot more of a workout that they would stopping a little bitty saw
blade that masses less than 1/1000 as much.

The physics on that seem interesting. A little like stopping a speeding
bullet on a dime--it challenges my imagination. Probably not quite as
difficult as stopping a lightning bolt, but I wouldn't want to try that
either.

Bill
No way a caliper could stop the blade in even 4X the time the
saw-stop does. And keeping dust out of the gap between tha "pad" and
the blade would be quite problematic - with dust decreasing the
stopping efficiency by a very large margin.

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.


When it snapped (seriously)? I'm not an engineer, so I don't know for
sure. I just wouldn't be surprised. Maybe someone else can opine.

Why would something that can stop a 4000 pound car "snap" when called on
to stop a 3 pound saw blade?

On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"
wrote:

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

Yes but the heat will do what to the saw blade?

Mark

In article , markem618
@hotmail.com says...

On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"
wrote:

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

Yes but the heat will do what to the saw blade?

About the same thing it does to a brake rotor I suspect, polish the
sides a little bit.

I doubt most people use a pusher stick to cut plywood sheets.

Now we have to define "close"...LOL



"Steve Turner" wrote in message
...
Would I be correct in assuming you were pushing the wood into the blade with
your bare hands rather than using a push jig or Gripper or something
similar?



On 10/12/2010 9:19 PM, Hoosierpopi wrote:
On Oct 12, 12:21 pm, Steve
wrote:

wildly advancing your fingers towards the blade,

As is done when, say, you are pushing a bit of wood into the saw and
it jerks out of place and you essentially "fall" forward now that the
wood is no longer offering resistance?

I've read that about five times and have tried to visualize what you're
talking
about, but I'm still puzzled.

Of course, the blade never stop turning at all on the saw I was using,
but I did manage to put three finges and a thumb in its path before
realizing I was cutting skin and bone - and jerked back.

Only cut clean through one digit and got it sewed and screwed back
on.

--
See Nad. See Nad go. Go Nad!
To reply, eat the taco.
http://www.flickr.com/photos/bbqboyee/

In article ,
says...

I doubt most people use a pusher stick to cut plywood sheets.

Now we have to define "close"...LOL

General rule is don't have your hands in in line with the blade, or
within 4 inches of it in any direction.

"Steve Turner" wrote in message
...
Would I be correct in assuming you were pushing the wood into the blade with
your bare hands rather than using a push jig or Gripper or something
similar?



On 10/12/2010 9:19 PM, Hoosierpopi wrote:
On Oct 12, 12:21 pm, Steve
wrote:

wildly advancing your fingers towards the blade,

As is done when, say, you are pushing a bit of wood into the saw and
it jerks out of place and you essentially "fall" forward now that the
wood is no longer offering resistance?

I've read that about five times and have tried to visualize what you're
talking
about, but I'm still puzzled.

Of course, the blade never stop turning at all on the saw I was using,
but I did manage to put three finges and a thumb in its path before
realizing I was cutting skin and bone - and jerked back.

Only cut clean through one digit and got it sewed and screwed back
on.

J. Clarke wrote:
In , says...

J. Clarke wrote:
In ,
says...

On Mon, 11 Oct 2010 19:59:30 -0400, wrote:

J. Clarke wrote:
In , says...

I would think that an emergency stop mechanism would be a whole different
magnitude than a scheduled, everyday, stop.

For a finger saver an emergency stop mechanism would have to stop the blade
in a few teeth passings. For everyday usage a couple dozen blade rotations
would be OK too. These two situations would require different tactics.

A dynamic electronic brake could vary the intensity for the two different
scenarios and we could add the caliper to the emerg stop. A caliper probably
wouldn't last long in everyday usage and would need to be adjusted and/or
replaced frequently.

So how much power do you have to put into that electronic brake to stop
the blade as fast as Sawstop's physical block?

And why would a caliper not last long? A set of brake pads on a car
with 10" rotors lasts 40,000 miles or so, and they're getting a Hell of
a lot more of a workout that they would stopping a little bitty saw
blade that masses less than 1/1000 as much.

The physics on that seem interesting. A little like stopping a speeding
bullet on a dime--it challenges my imagination. Probably not quite as
difficult as stopping a lightning bolt, but I wouldn't want to try that
either.

Bill
No way a caliper could stop the blade in even 4X the time the
saw-stop does. And keeping dust out of the gap between tha "pad" and
the blade would be quite problematic - with dust decreasing the
stopping efficiency by a very large margin.

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.


When it snapped (seriously)? I'm not an engineer, so I don't know for
sure. I just wouldn't be surprised. Maybe someone else can opine.

Why would something that can stop a 4000 pound car "snap" when called on
to stop a 3 pound saw blade?

"Pyrotechnics" rather than a master cylinder with brake fluid?

Bill

In article , says...

J. Clarke wrote:
In , says...

J. Clarke wrote:
In ,
says...

On Mon, 11 Oct 2010 19:59:30 -0400, wrote:

J. Clarke wrote:
In , says...

I would think that an emergency stop mechanism would be a whole different
magnitude than a scheduled, everyday, stop.

For a finger saver an emergency stop mechanism would have to stop the blade
in a few teeth passings. For everyday usage a couple dozen blade rotations
would be OK too. These two situations would require different tactics.

A dynamic electronic brake could vary the intensity for the two different
scenarios and we could add the caliper to the emerg stop. A caliper probably
wouldn't last long in everyday usage and would need to be adjusted and/or
replaced frequently.

So how much power do you have to put into that electronic brake to stop
the blade as fast as Sawstop's physical block?

And why would a caliper not last long? A set of brake pads on a car
with 10" rotors lasts 40,000 miles or so, and they're getting a Hell of
a lot more of a workout that they would stopping a little bitty saw
blade that masses less than 1/1000 as much.

The physics on that seem interesting. A little like stopping a speeding
bullet on a dime--it challenges my imagination. Probably not quite as
difficult as stopping a lightning bolt, but I wouldn't want to try that
either.

Bill
No way a caliper could stop the blade in even 4X the time the
saw-stop does. And keeping dust out of the gap between tha "pad" and
the blade would be quite problematic - with dust decreasing the
stopping efficiency by a very large margin.

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.


When it snapped (seriously)? I'm not an engineer, so I don't know for
sure. I just wouldn't be surprised. Maybe someone else can opine.

Why would something that can stop a 4000 pound car "snap" when called on
to stop a 3 pound saw blade?

"Pyrotechnics" rather than a master cylinder with brake fluid?

To stop the saw in a fraction of a revolution, you need rapid
application. A pyro will build pressure rapidly.

On 10/13/2010 08:45 AM, Josepi wrote:
I doubt most people use a pusher stick to cut plywood sheets.

First of all, he never said what kind of wood he was cutting, but from what he *did* say I
kinda doubt it was a sheet of plywood. Secondly, I said push "jig", not push "stick", and I
meant one of these:

http://www.tablesawpushstick.com/ima...k%20Safety.jpg

Of course, right there in the description they're calling it a push "stick", which I think
is erroneous. When I hear "push stick", I think of one of these pieces of crap:

http://woodzone.com/Merchant2/graphi...push-stick.jpg

which I would *never* use; they give me the willies. For plywood, it's entirely plausible
to use a "push block"

http://woodzone.com/Merchant2/graphi...push-block.jpg

Unless it's a really big sheet of plywood, I use these whenever I can on larger panels to
keep them against the fence and my hands away from the blade. I use a GRR-Ripper for almost
everything else that requires close proximity to the blade.

--
Free bad advice available here.
To reply, eat the taco.
http://www.flickr.com/photos/bbqboyee/

On Wed, 13 Oct 2010 09:12:15 -0400, "J. Clarke"
wrote:

In article , markem618
says...

On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"
wrote:

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

Yes but the heat will do what to the saw blade?

About the same thing it does to a brake rotor I suspect, polish the
sides a little bit.

Uneven heating of a metal disc also would cause it to warp. But then
again the "cartridge" in a Sawstop is toast when activated.

The two times I trimmed my finger nails with a tablesaw was it was a
Delta TS220 I had at the time, I was in a hurry impatient a bit tired,
which equalled being stupid.

The Unisaw which I have now seems safer, and that is more than a
reason to be careful.

Mark

J. Clarke wrote:

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

Bill
When it snapped (seriously)? I'm not an engineer, so I don't know for
sure. I just wouldn't be surprised. Maybe someone else can opine.

J. Clarke
Why would something that can stop a 4000 pound car "snap" when called on
to stop a 3 pound saw blade?

Bill
"Pyrotechnics" rather than a master cylinder with brake fluid?

J. Clarke
To stop the saw in a fraction of a revolution, you need rapid
application. A pyro will build pressure rapidly.

That is what I what I might expect to increase the probability of failure.

Given blade radius and density, and rpm, you could probably integrate to
compute the (foot-pounds of) energy that need to be stopped in a small
fraction of a second (I hope that the dust on the blade won't be an
issue). I've seen you post in another "forum" so I believe you are
up to the calculation. I do not have engineering background to back me
up, I'm just thinking it through with you and everyone else who is
reading. Evidently, you'll need to generate the equivalent of an equal
and opposite amount of energy. This means, I think, that you only get
the benefit of a "projection" (dot product) and not all of the force you
can apply to the side of the blade. My reasoning could definitely be
off, maybe a physicist or engineer could help out?

Regards,
Bill

J. Clarke wrote:


As is done when, say, you are pushing a bit of wood into the saw and
it jerks out of place and you essentially "fall" forward now that the
wood is no longer offering resistance?

I've read that about five times and have tried to visualize what you're
talking
about, but I'm still puzzled.

Think about what would happen if you were walking with a cane, and the
tip of the cane slipped on some ice. It's analogous.

Bill

On 10/13/10 7:44 AM, Markem wrote:
On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"
wrote:

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

Yes but the heat will do what to the saw blade?

Mark

Nothing.
A lot more heat is generated by cutting than would be generated in the
half second it would take to slow down the blade.

You guys do realize we're not leaving the motor on in this scenario,
right? :-)


--

-MIKE-

"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com

---remove "DOT" ^^^^ to reply

On 10/13/10 9:43 AM, J. Clarke wrote:
In , says...

J. Clarke wrote:
In , says...

J. Clarke wrote:
In ,
says...

On Mon, 11 Oct 2010 19:59:30 -0400, wrote:

J. Clarke wrote:
In , says...

I would think that an emergency stop mechanism would be a whole different
magnitude than a scheduled, everyday, stop.

For a finger saver an emergency stop mechanism would have to stop the blade
in a few teeth passings. For everyday usage a couple dozen blade rotations
would be OK too. These two situations would require different tactics.

A dynamic electronic brake could vary the intensity for the two different
scenarios and we could add the caliper to the emerg stop. A caliper probably
wouldn't last long in everyday usage and would need to be adjusted and/or
replaced frequently.

So how much power do you have to put into that electronic brake to stop
the blade as fast as Sawstop's physical block?

And why would a caliper not last long? A set of brake pads on a car
with 10" rotors lasts 40,000 miles or so, and they're getting a Hell of
a lot more of a workout that they would stopping a little bitty saw
blade that masses less than 1/1000 as much.

The physics on that seem interesting. A little like stopping a speeding
bullet on a dime--it challenges my imagination. Probably not quite as
difficult as stopping a lightning bolt, but I wouldn't want to try that
either.

Bill
No way a caliper could stop the blade in even 4X the time the
saw-stop does. And keeping dust out of the gap between tha "pad" and
the blade would be quite problematic - with dust decreasing the
stopping efficiency by a very large margin.

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.


When it snapped (seriously)? I'm not an engineer, so I don't know for
sure. I just wouldn't be surprised. Maybe someone else can opine.

Why would something that can stop a 4000 pound car "snap" when called on
to stop a 3 pound saw blade?

"Pyrotechnics" rather than a master cylinder with brake fluid?

To stop the saw in a fraction of a revolution, you need rapid
application. A pyro will build pressure rapidly.

I didn't think we were talking about an emergency stop.
AFAIK, we're discussing a convenience stop which, in my opinion, would
be satisfactorily done in a couple seconds, not milliseconds.


--

-MIKE-

"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com

---remove "DOT" ^^^^ to reply

-MIKE- wrote:
On 10/13/10 7:44 AM, Markem wrote:
On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"
wrote:

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

Yes but the heat will do what to the saw blade?

Mark

Nothing.
A lot more heat is generated by cutting than would be generated in the
half second it would take to slow down the blade.

You guys do realize we're not leaving the motor on in this scenario,
right? :-)


Yep, thought of that. Gotta break the problem into parts (important
trick/secret!) : ) I didn't count the mass of the rotor either, or it's
attached parts, in my other post either. I'm curious now though about
the calculation (foot/lbs of force).

Bill

-MIKE- wrote:
On 10/13/10 9:43 AM, J. Clarke wrote:
In , says...

J. Clarke wrote:
In , says...

J. Clarke wrote:
In ,
says...

On Mon, 11 Oct 2010 19:59:30 -0400, wrote:

J. Clarke wrote:
In ,
says...

I would think that an emergency stop mechanism would be a
whole different
magnitude than a scheduled, everyday, stop.

For a finger saver an emergency stop mechanism would have to
stop the blade
in a few teeth passings. For everyday usage a couple dozen
blade rotations
would be OK too. These two situations would require different
tactics.

A dynamic electronic brake could vary the intensity for the
two different
scenarios and we could add the caliper to the emerg stop. A
caliper probably
wouldn't last long in everyday usage and would need to be
adjusted and/or
replaced frequently.

So how much power do you have to put into that electronic brake
to stop
the blade as fast as Sawstop's physical block?

And why would a caliper not last long? A set of brake pads on a
car
with 10" rotors lasts 40,000 miles or so, and they're getting a
Hell of
a lot more of a workout that they would stopping a little bitty
saw
blade that masses less than 1/1000 as much.

The physics on that seem interesting. A little like stopping a
speeding
bullet on a dime--it challenges my imagination. Probably not
quite as
difficult as stopping a lightning bolt, but I wouldn't want to
try that
either.

Bill
No way a caliper could stop the blade in even 4X the time the
saw-stop does. And keeping dust out of the gap between tha "pad" and
the blade would be quite problematic - with dust decreasing the
stopping efficiency by a very large margin.

I suspect that a small pyrotechnic pressurizing one of the
calipers off
my '76 Lincoln might surprise you.


When it snapped (seriously)? I'm not an engineer, so I don't know for
sure. I just wouldn't be surprised. Maybe someone else can opine.

Why would something that can stop a 4000 pound car "snap" when
called on
to stop a 3 pound saw blade?

"Pyrotechnics" rather than a master cylinder with brake fluid?

To stop the saw in a fraction of a revolution, you need rapid
application. A pyro will build pressure rapidly.

I didn't think we were talking about an emergency stop.
AFAIK, we're discussing a convenience stop which, in my opinion, would
be satisfactorily done in a couple seconds, not milliseconds.


I thought we were discussing a stop on the same order as SawStop.
I didn't read every post in the thread.

Bill

On 10/13/10 11:22 AM, Bill wrote:
-MIKE- wrote:
On 10/13/10 7:44 AM, Markem wrote:
On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"
wrote:

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

Yes but the heat will do what to the saw blade?

Mark

Nothing.
A lot more heat is generated by cutting than would be generated in the
half second it would take to slow down the blade.

You guys do realize we're not leaving the motor on in this scenario,
right? :-)


Yep, thought of that. Gotta break the problem into parts (important
trick/secret!) : ) I didn't count the mass of the rotor either, or it's
attached parts, in my other post either. I'm curious now though about
the calculation (foot/lbs of force).

Bill


Sometimes all it takes is a couple of scraps of wood to show how
"little" force is needed. Haven't you ever stopped a coasting blade with
a scrap of wood?

I still see people talking about the SawStop and what it takes for an
emergency stop of the blade. I don't know about anyone else, but all I'm
talking about is a convenience stop.
I suspect a blade could be stopped (at shut-off) in less that a second
with something the size of a bicycle brake and a spring.


--

-MIKE-

"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com

---remove "DOT" ^^^^ to reply

On 10/13/10 11:30 AM, Bill wrote:
-MIKE- wrote:
On 10/13/10 9:43 AM, J. Clarke wrote:
In , says...

J. Clarke wrote:
In , says...

J. Clarke wrote:
In ,
says...

On Mon, 11 Oct 2010 19:59:30 -0400, wrote:

J. Clarke wrote:
In ,
says...

I would think that an emergency stop mechanism would be a
whole different
magnitude than a scheduled, everyday, stop.

For a finger saver an emergency stop mechanism would have to
stop the blade
in a few teeth passings. For everyday usage a couple dozen
blade rotations
would be OK too. These two situations would require different
tactics.

A dynamic electronic brake could vary the intensity for the
two different
scenarios and we could add the caliper to the emerg stop. A
caliper probably
wouldn't last long in everyday usage and would need to be
adjusted and/or
replaced frequently.

So how much power do you have to put into that electronic brake
to stop
the blade as fast as Sawstop's physical block?

And why would a caliper not last long? A set of brake pads on a
car
with 10" rotors lasts 40,000 miles or so, and they're getting a
Hell of
a lot more of a workout that they would stopping a little bitty
saw
blade that masses less than 1/1000 as much.

The physics on that seem interesting. A little like stopping a
speeding
bullet on a dime--it challenges my imagination. Probably not
quite as
difficult as stopping a lightning bolt, but I wouldn't want to
try that
either.

Bill
No way a caliper could stop the blade in even 4X the time the
saw-stop does. And keeping dust out of the gap between tha "pad"
and
the blade would be quite problematic - with dust decreasing the
stopping efficiency by a very large margin.

I suspect that a small pyrotechnic pressurizing one of the
calipers off
my '76 Lincoln might surprise you.


When it snapped (seriously)? I'm not an engineer, so I don't know for
sure. I just wouldn't be surprised. Maybe someone else can opine.

Why would something that can stop a 4000 pound car "snap" when
called on
to stop a 3 pound saw blade?

"Pyrotechnics" rather than a master cylinder with brake fluid?

To stop the saw in a fraction of a revolution, you need rapid
application. A pyro will build pressure rapidly.

I didn't think we were talking about an emergency stop.
AFAIK, we're discussing a convenience stop which, in my opinion, would
be satisfactorily done in a couple seconds, not milliseconds.


I thought we were discussing a stop on the same order as SawStop.
I didn't read every post in the thread.

Bill


Someone brought SawStop into the discussion, which took things on a
tangent.
We started out discussing the OP's link to a set of motor reversing
instructions as a way to slow down the blade for convenience. Then I
proposed the use of a bicycle brake... and things went from there.


--

-MIKE-

"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com

---remove "DOT" ^^^^ to reply

-MIKE- wrote:
On 10/13/10 11:30 AM, Bill wrote:
-MIKE- wrote:
On 10/13/10 9:43 AM, J. Clarke wrote:
In , says...

J. Clarke wrote:
In , says...

J. Clarke wrote:
In ,
says...

On Mon, 11 Oct 2010 19:59:30 -0400, wrote:

J. Clarke wrote:
In ,
says...

I would think that an emergency stop mechanism would be a
whole different
magnitude than a scheduled, everyday, stop.

For a finger saver an emergency stop mechanism would have to
stop the blade
in a few teeth passings. For everyday usage a couple dozen
blade rotations
would be OK too. These two situations would require different
tactics.

A dynamic electronic brake could vary the intensity for the
two different
scenarios and we could add the caliper to the emerg stop. A
caliper probably
wouldn't last long in everyday usage and would need to be
adjusted and/or
replaced frequently.

So how much power do you have to put into that electronic brake
to stop
the blade as fast as Sawstop's physical block?

And why would a caliper not last long? A set of brake pads on a
car
with 10" rotors lasts 40,000 miles or so, and they're getting a
Hell of
a lot more of a workout that they would stopping a little bitty
saw
blade that masses less than 1/1000 as much.

The physics on that seem interesting. A little like stopping a
speeding
bullet on a dime--it challenges my imagination. Probably not
quite as
difficult as stopping a lightning bolt, but I wouldn't want to
try that
either.

Bill
No way a caliper could stop the blade in even 4X the time the
saw-stop does. And keeping dust out of the gap between tha "pad"
and
the blade would be quite problematic - with dust decreasing the
stopping efficiency by a very large margin.

I suspect that a small pyrotechnic pressurizing one of the
calipers off
my '76 Lincoln might surprise you.


When it snapped (seriously)? I'm not an engineer, so I don't know
for
sure. I just wouldn't be surprised. Maybe someone else can opine.

Why would something that can stop a 4000 pound car "snap" when
called on
to stop a 3 pound saw blade?

"Pyrotechnics" rather than a master cylinder with brake fluid?

To stop the saw in a fraction of a revolution, you need rapid
application. A pyro will build pressure rapidly.

I didn't think we were talking about an emergency stop.
AFAIK, we're discussing a convenience stop which, in my opinion, would
be satisfactorily done in a couple seconds, not milliseconds.


I thought we were discussing a stop on the same order as SawStop.
I didn't read every post in the thread.

Bill


Someone brought SawStop into the discussion, which took things on a
tangent.
We started out discussing the OP's link to a set of motor reversing
instructions as a way to slow down the blade for convenience. Then I
proposed the use of a bicycle brake... and things went from there.

Properly done, I bicycle brake sounds like a good idea! I'd hate to
read about flying parts.

Bill

On 10/13/2010 12:00 PM, Bill wrote:
-MIKE- wrote:
Someone brought SawStop into the discussion, which took things on a
tangent.
We started out discussing the OP's link to a set of motor reversing
instructions as a way to slow down the blade for convenience. Then I
proposed the use of a bicycle brake... and things went from there.

Properly done, I bicycle brake sounds like a good idea! I'd hate to read about flying parts.

AHEM. I believe *I* was the one who proposed the use of the bicycle brake. That -MIKE-
character is trying to steal my idea. :-)

--
Free bad advice available here.
To reply, eat the taco.
http://www.flickr.com/photos/bbqboyee/

On 10/13/10 12:06 PM, Steve Turner wrote:
On 10/13/2010 12:00 PM, Bill wrote:
-MIKE- wrote:
Someone brought SawStop into the discussion, which took things on a
tangent.
We started out discussing the OP's link to a set of motor reversing
instructions as a way to slow down the blade for convenience. Then I
proposed the use of a bicycle brake... and things went from there.

Properly done, I bicycle brake sounds like a good idea! I'd hate to
read about flying parts.

AHEM. I believe *I* was the one who proposed the use of the bicycle
brake. That -MIKE- character is trying to steal my idea. :-)


Welllll, looks like I own someone a beer.
Yeppers, I said, "...aftermarket saw brake, under the table.... pads or
rollers or whatever, that would squeeze the blade," and then you brought
up the bike brake.

A good inventor is a better thief. :-)


--

-MIKE-

"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com

---remove "DOT" ^^^^ to reply

In article ,
says...

On 10/13/10 9:43 AM, J. Clarke wrote:
In , says...

J. Clarke wrote:
In , says...

J. Clarke wrote:
In ,
says...

On Mon, 11 Oct 2010 19:59:30 -0400, wrote:

J. Clarke wrote:
In , says...

I would think that an emergency stop mechanism would be a whole different
magnitude than a scheduled, everyday, stop.

For a finger saver an emergency stop mechanism would have to stop the blade
in a few teeth passings. For everyday usage a couple dozen blade rotations
would be OK too. These two situations would require different tactics.

A dynamic electronic brake could vary the intensity for the two different
scenarios and we could add the caliper to the emerg stop. A caliper probably
wouldn't last long in everyday usage and would need to be adjusted and/or
replaced frequently.

So how much power do you have to put into that electronic brake to stop
the blade as fast as Sawstop's physical block?

And why would a caliper not last long? A set of brake pads on a car
with 10" rotors lasts 40,000 miles or so, and they're getting a Hell of
a lot more of a workout that they would stopping a little bitty saw
blade that masses less than 1/1000 as much.

The physics on that seem interesting. A little like stopping a speeding
bullet on a dime--it challenges my imagination. Probably not quite as
difficult as stopping a lightning bolt, but I wouldn't want to try that
either.

Bill
No way a caliper could stop the blade in even 4X the time the
saw-stop does. And keeping dust out of the gap between tha "pad" and
the blade would be quite problematic - with dust decreasing the
stopping efficiency by a very large margin.

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.


When it snapped (seriously)? I'm not an engineer, so I don't know for
sure. I just wouldn't be surprised. Maybe someone else can opine.

Why would something that can stop a 4000 pound car "snap" when called on
to stop a 3 pound saw blade?

"Pyrotechnics" rather than a master cylinder with brake fluid?

To stop the saw in a fraction of a revolution, you need rapid
application. A pyro will build pressure rapidly.

I didn't think we were talking about an emergency stop.
AFAIK, we're discussing a convenience stop which, in my opinion, would
be satisfactorily done in a couple seconds, not milliseconds.

Well, geez, for that a bicycle brake will work fine.

In article , says...

J. Clarke wrote:

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

Bill
When it snapped (seriously)? I'm not an engineer, so I don't know for
sure. I just wouldn't be surprised. Maybe someone else can opine.

J. Clarke
Why would something that can stop a 4000 pound car "snap" when called on
to stop a 3 pound saw blade?

Bill
"Pyrotechnics" rather than a master cylinder with brake fluid?

J. Clarke
To stop the saw in a fraction of a revolution, you need rapid
application. A pyro will build pressure rapidly.

That is what I what I might expect to increase the probability of failure.

Given blade radius and density, and rpm, you could probably integrate to
compute the (foot-pounds of) energy that need to be stopped in a small
fraction of a second (I hope that the dust on the blade won't be an
issue). I've seen you post in another "forum" so I believe you are
up to the calculation. I do not have engineering background to back me
up, I'm just thinking it through with you and everyone else who is
reading. Evidently, you'll need to generate the equivalent of an equal
and opposite amount of energy. This means, I think, that you only get
the benefit of a "projection" (dot product) and not all of the force you
can apply to the side of the blade. My reasoning could definitely be
off, maybe a physicist or engineer could help out?

Disk brakes work by friction. The energy comes off as heat. Apply F to
the brake, k * F is the braking force where k is the coefficient of
friction.

Back of the envelope it looks like the Lincoln brake at Lincoln pressure
can stop it in about 1/3 revolution. Don't know how much higher
pressure that caliper can take--at 2x the pressure might be able to do
it in 1/6 revolution, which puts it in Sawstop territory.

In article ,
says...

On 10/13/10 12:06 PM, Steve Turner wrote:
On 10/13/2010 12:00 PM, Bill wrote:
-MIKE- wrote:
Someone brought SawStop into the discussion, which took things on a
tangent.
We started out discussing the OP's link to a set of motor reversing
instructions as a way to slow down the blade for convenience. Then I
proposed the use of a bicycle brake... and things went from there.

Properly done, I bicycle brake sounds like a good idea! I'd hate to
read about flying parts.

AHEM. I believe *I* was the one who proposed the use of the bicycle
brake. That -MIKE- character is trying to steal my idea. :-)


Welllll, looks like I own someone a beer.
Yeppers, I said, "...aftermarket saw brake, under the table.... pads or
rollers or whatever, that would squeeze the blade," and then you brought
up the bike brake.

A good inventor is a better thief. :-)

And Nikolai Yvanovich Lobachevski is his _name_ . . .

In article , says...

J. Clarke wrote:


As is done when, say, you are pushing a bit of wood into the saw and
it jerks out of place and you essentially "fall" forward now that the
wood is no longer offering resistance?

I've read that about five times and have tried to visualize what you're
talking
about, but I'm still puzzled.

Think about what would happen if you were walking with a cane, and the
tip of the cane slipped on some ice. It's analogous.

Uh, J. Clarke didn't write _any_ of that.

Steve Turner wrote in
:

*snip*

Of course, right there in the description they're calling it a push
"stick", which I think is erroneous. When I hear "push stick", I
think of one of these pieces of crap:

http://woodzone.com/Merchant2/graphi...push-stick.jpg

which I would *never* use; they give me the willies. For plywood,
it's entirely plausible to use a "push block"


*snip*

Trust your feelings, Steve.

I used that style of push stick for years, until I was cutting a small
piece and pressure on only the one point caused the piece to move and
catch on the back of the blade. The resulting kickback hit me in the
dust mask and broke the push stick. I will not use that style again.

Puckdropper
--
Never teach your apprentice everything you know.

On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"
wrote:

In article ,
says...

On Mon, 11 Oct 2010 19:59:30 -0400, Bill wrote:

J. Clarke wrote:
In , says...

I would think that an emergency stop mechanism would be a whole different
magnitude than a scheduled, everyday, stop.

For a finger saver an emergency stop mechanism would have to stop the blade
in a few teeth passings. For everyday usage a couple dozen blade rotations
would be OK too. These two situations would require different tactics.

A dynamic electronic brake could vary the intensity for the two different
scenarios and we could add the caliper to the emerg stop. A caliper probably
wouldn't last long in everyday usage and would need to be adjusted and/or
replaced frequently.

So how much power do you have to put into that electronic brake to stop
the blade as fast as Sawstop's physical block?

And why would a caliper not last long? A set of brake pads on a car
with 10" rotors lasts 40,000 miles or so, and they're getting a Hell of
a lot more of a workout that they would stopping a little bitty saw
blade that masses less than 1/1000 as much.

The physics on that seem interesting. A little like stopping a speeding
bullet on a dime--it challenges my imagination. Probably not quite as
difficult as stopping a lightning bolt, but I wouldn't want to try that
either.

Bill
No way a caliper could stop the blade in even 4X the time the
saw-stop does. And keeping dust out of the gap between tha "pad" and
the blade would be quite problematic - with dust decreasing the
stopping efficiency by a very large margin.

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

But would also be totally impractical on a 10" saw.

On Wed, 13 Oct 2010 11:37:59 -0500, -MIKE-
wrote:

On 10/13/10 11:22 AM, Bill wrote:
-MIKE- wrote:
On 10/13/10 7:44 AM, Markem wrote:
On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"
wrote:

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

Yes but the heat will do what to the saw blade?

Mark

Nothing.
A lot more heat is generated by cutting than would be generated in the
half second it would take to slow down the blade.

You guys do realize we're not leaving the motor on in this scenario,
right? :-)


Yep, thought of that. Gotta break the problem into parts (important
trick/secret!) : ) I didn't count the mass of the rotor either, or it's
attached parts, in my other post either. I'm curious now though about
the calculation (foot/lbs of force).

Bill


Sometimes all it takes is a couple of scraps of wood to show how
"little" force is needed. Haven't you ever stopped a coasting blade with
a scrap of wood?

I still see people talking about the SawStop and what it takes for an
emergency stop of the blade. I don't know about anyone else, but all I'm
talking about is a convenience stop.
I suspect a blade could be stopped (at shut-off) in less that a second
with something the size of a bicycle brake and a spring.

Use a DC motor and a DPDT switch with a big resistor across the "stop"
terminals to short the motor when you shut it off. Stop a 10 inch
blade from 3600rpm in less trha a second with a dead short (if the
switch can handle it) or in about 2 seconds with a good "soft" braking
resistor.

In article ,
says...

On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"
wrote:

In article ,
says...

On Mon, 11 Oct 2010 19:59:30 -0400, Bill wrote:

J. Clarke wrote:
In , says...

I would think that an emergency stop mechanism would be a whole different
magnitude than a scheduled, everyday, stop.

For a finger saver an emergency stop mechanism would have to stop the blade
in a few teeth passings. For everyday usage a couple dozen blade rotations
would be OK too. These two situations would require different tactics.

A dynamic electronic brake could vary the intensity for the two different
scenarios and we could add the caliper to the emerg stop. A caliper probably
wouldn't last long in everyday usage and would need to be adjusted and/or
replaced frequently.

So how much power do you have to put into that electronic brake to stop
the blade as fast as Sawstop's physical block?

And why would a caliper not last long? A set of brake pads on a car
with 10" rotors lasts 40,000 miles or so, and they're getting a Hell of
a lot more of a workout that they would stopping a little bitty saw
blade that masses less than 1/1000 as much.

The physics on that seem interesting. A little like stopping a speeding
bullet on a dime--it challenges my imagination. Probably not quite as
difficult as stopping a lightning bolt, but I wouldn't want to try that
either.

Bill
No way a caliper could stop the blade in even 4X the time the
saw-stop does. And keeping dust out of the gap between tha "pad" and
the blade would be quite problematic - with dust decreasing the
stopping efficiency by a very large margin.

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

But would also be totally impractical on a 10" saw.

Why would it be "impractical on a 10" saw? The brake rotors on that car
are IIRC 11.5 inch diameter and the whole brake assembly fits inside a
15" wheel.

In article ,
says...

On Wed, 13 Oct 2010 11:37:59 -0500, -MIKE-
wrote:

On 10/13/10 11:22 AM, Bill wrote:
-MIKE- wrote:
On 10/13/10 7:44 AM, Markem wrote:
On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"
wrote:

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

Yes but the heat will do what to the saw blade?

Mark

Nothing.
A lot more heat is generated by cutting than would be generated in the
half second it would take to slow down the blade.

You guys do realize we're not leaving the motor on in this scenario,
right? :-)


Yep, thought of that. Gotta break the problem into parts (important
trick/secret!) : ) I didn't count the mass of the rotor either, or it's
attached parts, in my other post either. I'm curious now though about
the calculation (foot/lbs of force).

Bill


Sometimes all it takes is a couple of scraps of wood to show how
"little" force is needed. Haven't you ever stopped a coasting blade with
a scrap of wood?

I still see people talking about the SawStop and what it takes for an
emergency stop of the blade. I don't know about anyone else, but all I'm
talking about is a convenience stop.
I suspect a blade could be stopped (at shut-off) in less that a second
with something the size of a bicycle brake and a spring.

Use a DC motor and a DPDT switch with a big resistor across the "stop"
terminals to short the motor when you shut it off. Stop a 10 inch
blade from 3600rpm in less trha a second with a dead short (if the
switch can handle it) or in about 2 seconds with a good "soft" braking
resistor.

Which is where this thread started.

J. Clarke wrote:
In , says...

J. Clarke wrote:

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

Bill
When it snapped (seriously)? I'm not an engineer, so I don't know for
sure. I just wouldn't be surprised. Maybe someone else can opine.

J. Clarke
Why would something that can stop a 4000 pound car "snap" when called on
to stop a 3 pound saw blade?

Bill
"Pyrotechnics" rather than a master cylinder with brake fluid?

J. Clarke
To stop the saw in a fraction of a revolution, you need rapid
application. A pyro will build pressure rapidly.

That is what I what I might expect to increase the probability of failure.

Given blade radius and density, and rpm, you could probably integrate to
compute the (foot-pounds of) energy that need to be stopped in a small
fraction of a second (I hope that the dust on the blade won't be an
issue). I've seen you post in another "forum" so I believe you are
up to the calculation. I do not have engineering background to back me
up, I'm just thinking it through with you and everyone else who is
reading. Evidently, you'll need to generate the equivalent of an equal
and opposite amount of energy. This means, I think, that you only get
the benefit of a "projection" (dot product) and not all of the force you
can apply to the side of the blade. My reasoning could definitely be
off, maybe a physicist or engineer could help out?

Disk brakes work by friction. The energy comes off as heat. Apply F to
the brake, k * F is the braking force where k is the coefficient of
friction.

Back of the envelope it looks like the Lincoln brake at Lincoln pressure
can stop it in about 1/3 revolution. Don't know how much higher
pressure that caliper can take--at 2x the pressure might be able to do
it in 1/6 revolution, which puts it in Sawstop territory.

Interesting. Thank you. I'm not sure about your "imposter"..

Bill

On Wed, 13 Oct 2010 18:16:40 -0400, "J. Clarke"
wrote:

Use a DC motor and a DPDT switch with a big resistor across the "stop"
terminals to short the motor when you shut it off. Stop a 10 inch
blade from 3600rpm in less trha a second with a dead short (if the
switch can handle it) or in about 2 seconds with a good "soft" braking
resistor.

Which is where this thread started.


A really big solid state relay and a sealed explosion proof switch,
cause you do not want to start a thread about sawdust explosions.
Right?

You know you can use oars to stir stuff.

Mark

I think the main pint for all of us is


*** think *** about what could happen and then prevent it.

In safety training they call this a "barrier"
Minimize the chances with a "barrier". If you cannot absolutely prevent it
think
"Do I have to do this at all" and "Is there another way" and "How can I
make is less risk"

Minimize the damage, if should it happen anyway.



"Puckdropper" puckdropper(at)yahoo(dot)com wrote in message
b.com...

Trust your feelings, Steve.

I used that style of push stick for years, until I was cutting a small
piece and pressure on only the one point caused the piece to move and
catch on the back of the blade. The resulting kickback hit me in the
dust mask and broke the push stick. I will not use that style again.

Puckdropper
--
Never teach your apprentice everything you know.

Can we drink beer in court?


"J. Clarke" wrote in message
in.local...
And Nikolai Yvanovich Lobachevski is his _name_ . . .


Welllll, looks like I own someone a beer.
Yeppers, I said, "...aftermarket saw brake, under the table.... pads or
rollers or whatever, that would squeeze the blade," and then you brought
up the bike brake.