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'[EE]: sawstop'
2006\08\17@140954 by Dave Lag

picon face
Interesting update on the sawstop
http://www.designnews.com/CA6360672.html

.........snip....
Lathrop and Young on the sawstop:
(http://www.sawstop.com)
>It is neat to watch them shove a raw hotdog into the blade and it
> stops. Not very practical if you are mowing rocks though.

Or trying to saw hotdogs.

2006\08\17@150830 by David VanHorn

picon face
On 8/17/06, Dave Lag <spam_OUTdavescomputerTakeThisOuTspamrogers.com> wrote:
>
> Interesting update on the sawstop
> http://www.designnews.com/CA6360672.html
>
> .........snip....
> Lathrop and Young on the sawstop:
> (http://www.sawstop.com)
> >It is neat to watch them shove a raw hotdog into the blade and it
> > stops. Not very practical if you are mowing rocks though.
>
> Or trying to saw hotdogs.



Or metals, or anything moderately conductive it seems,
Capacitance sensor.

2006\08\17@151256 by David VanHorn

picon face
Ouch!  It's also a one-shot deal.


Stopping the blade is another matter, made more difficult by the speed with
which it must happen.

"You have to stop a 4,000-rpm blade in a few thousandths of a second, or
it's too late," Gass says.

To do so, Gass employs a compressed spring, held back by a 10 thousandths of
an inch fuse wire. When the DSP recognizes flesh, it signals a capacitor to
send a surge of electrical current, vaporizing the fuse wire in
approximately 15 millionths of a second. When the fuse wire vaporizes, it
releases the spring brake, stopping the blade.

Gass says the blade typically stops in about three thousandths of a second.

2006\08\17@152627 by Randy Glenn

picon face
According to the videos and testimonials on their site, it takes about
5 minutes to replace a brake, and a brake costs about $70.

Far less than a finger.

On 8/17/06, David VanHorn <.....dvanhornKILLspamspam@spam@microbrix.com> wrote:
{Quote hidden}

> -

2006\08\17@155959 by peter green

flavicon
face

> According to the videos and testimonials on their site, it takes about
> 5 minutes to replace a brake, and a brake costs about $70.
>
> Far less than a finger.
the question is how often will it trigger when it shouldn't, those $70
replacements will add up pretty quick if it mistriggers once a week or so.

2006\08\17@171444 by Robert Rolf

picon face
peter green wrote:

>>According to the videos and testimonials on their site, it takes about
>>5 minutes to replace a brake, and a brake costs about $70.
>>
>>Far less than a finger.
>
> the question is how often will it trigger when it shouldn't, those $70
> replacements will add up pretty quick if it mistriggers once a week or so.

Yep.
The design relies on a fast blow fuse to trigger the catch.
Surely it could be designed to be resettable with a user replaceable
fuse cartridge.
Yes, a lot of energy is being dissipated, but if the trigger mass is
small, it can be quickly moved (electro magnetic catch instead).

Robert

2006\08\17@190440 by VULCAN20

picon face
And what would happen if you tried to cut damp wood or some with a high
moisture content.

Bob

peter green wrote:

{Quote hidden}

2006\08\17@192647 by Dave Lag

picon face
peter green wrote:
>>According to the videos and testimonials on their site, it takes about
>>5 minutes to replace a brake, and a brake costs about $70.
>>
>>Far less than a finger.
>
> the question is how often will it trigger when it shouldn't, those $70
> replacements will add up pretty quick if it mistriggers once a week or so.
>
Agreed.
Despite the guys impressive credentials I get the impression he really
messed up his business plan,ie: the above, p.o. your market, ask too
much in royalties, end run via government etc..

2006\08\17@192752 by Bob Blick

face picon face
On 17 Aug 2006 at 18:04, VULCAN20 wrote:

> And what would happen if you tried to cut damp wood or some with a high
> moisture content.

$70 per cut if you forget to push the override button(if there is one).

The inventor has been pushing this product for years, and is now
trying to make it the law.

Cheers,

Bob

2006\08\17@203356 by VULCAN20

picon face
I have worked with power saws for the last 48 years of my life 5 of
these years as a maintenance man in a wood working factory.

from the pictures I have seen of this it appears to me that all he does
is pop the blade down into the top of a power saw. Has any one seen any
figures on how fast he actually stops the rotation of the saw.  I would
love to see how he does this with the following types of saws:
Band saw, radial arm saw, all the many varieties of power chop saws,
miter saws, hand power circular saw.

I  saw a demo of a system years ago where the operator had to wear
special gloves it worked on the principle of a certain type of light UV
or some thing or polarized light,  the glove were reflective some
thing.  The idea was if the fingers came within a certain distance of
the blade the blade would stop in about 1 seconds time.  It would not
stop a cut but maybe losing several fingers. But then no gloves no
protection.

So as I see it he is only touching a small percentage of the power saws
out there.

Bob



Bob Blick wrote:

{Quote hidden}

2006\08\17@210544 by Robert Rolf

picon face
Seems to me that some sort of longwave passive IR detection would
be the way to go. Then the conductivity of the material
wouldn't matter. Only the heat from finger/hand would trigger
the blade brake. And the guard region could be moved back from
actual blade contact, to just milimeters away. Trick would be
keeping the sawdust from being a problem (hence the original idea
using capacitance sensing).



Robert

VULCAN20 wrote:

{Quote hidden}

2006\08\17@223507 by Gus S Calabrese

face picon face
Surely the brake mechanism can be made for less than the $70  
replacement cost.
choosing the correct blade to shaft interconnect ( to reduce  
rotational inertia )
should allow one to stop a blade in less than 1/2 rotation.

4000 rpm means 15 milliseconds per rotation.  Stopping the blade in  
1/3 of a rotation
can probably be done without destroying the blade or requiring much  
of a reset.  If the
blade is magnetically coupled to the drive shaft, the decoupling can  
occur in 5 milliseconds
and the stop blade can do it's thing.

Excluding the sensors, ( I leave that up to you guys ), the rest of  
the mechanism can be made
for $50 or less and tripped hundreds of times.  This makes false  
triggers not much of a big deal.

AGSC


On 2006-Aug 17, at 13:08hrs PM, David VanHorn wrote:

On 8/17/06, Dave Lag <davescomputerspamKILLspamrogers.com> wrote:
{Quote hidden}

Or metals, or anything moderately conductive it seems,
Capacitance sensor.

2006\08\17@224250 by Gerhard Fiedler

picon face
VULCAN20 wrote:

> from the pictures I have seen of this it appears to me that all he does
> is pop the blade down into the top of a power saw. Has any one seen any
> figures on how fast he actually stops the rotation of the saw.

It's described how they do it and also how fast it acts. Of course you'd
have to read the descriptions in addition to looking at the pictures :)

> So as I see it he is only touching a small percentage of the power saws
> out there.

Even if so, so what? I don't know how well it works, but there's plenty of
equipment that works well for one application and not for others. The fact
that it may not work for other applications is not really an argument at
all.

Gerhard

2006\08\18@005512 by Herbert Graf

flavicon
face
On Thu, 2006-08-17 at 14:12 -0400, Dave Lag wrote:
> Interesting update on the sawstop
> http://www.designnews.com/CA6360672.html
>
> .........snip....
> Lathrop and Young on the sawstop:
> (http://www.sawstop.com)
>  >It is neat to watch them shove a raw hotdog into the blade and it
>  > stops. Not very practical if you are mowing rocks though.

While the idea is very interesting, I do have a problem with the way
he's approached getting his idea "accepted": by basically lobbying the
government to FORCE the manufacturers to use some technology, likely
his.

Anytime somebody tries to shove their product down the throats of
consumers it bugs me.

Frankly, I don't see any reason this sort of thing SHOULD be mandated. A
person using a table saw is FULLY aware of what it's capable of. As long
as sufficient measures are taken to prevent persons who aren't aware of
what a saw can do (i.e. children) from using the saw, I see NO reason to
force consumers to pay additional money (both up front, and false
triggers).

We'll see how this turns out, but based on how this guy as approached
trying to get his product sold, I am NOT wishing him luck.

TTYL

2006\08\18@005754 by Herbert Graf

flavicon
face
On Thu, 2006-08-17 at 19:05 -0600, Robert Rolf wrote:
> Seems to me that some sort of longwave passive IR detection would
> be the way to go. Then the conductivity of the material
> wouldn't matter. Only the heat from finger/hand would trigger
> the blade brake. And the guard region could be moved back from
> actual blade contact, to just milimeters away. Trick would be
> keeping the sawdust from being a problem (hence the original idea
> using capacitance sensing).

But then "warm" wood would trigger it, i.e. wood in my car in the sun
for an hour. Heck, even doing a cut on a piece of hardware would
probably warm it up enough to trigger.

TTYL



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