Hi all ;
Can anyone provide a <somewhat > scientific .. yet
<simple> explanation - of how the saw-stop
_detection_ works ?
I saw a demonstration - and cannot figure out why :
: it works on a finger
: it works on a hot dog - being held by a finger
.. but not on a hot dog that is not held by a finger !
I'm really missing something - and it's driving me crazy !
John T.
--- news://freenews.netfront.net/ - complaints: [email protected] ---
On 8/19/2014 5:13 PM, [email protected] wrote:
> Hi all ;
>
> Can anyone provide a <somewhat > scientific .. yet
> <simple> explanation - of how the saw-stop
> _detection_ works ?
> I saw a demonstration - and cannot figure out why :
> : it works on a finger
> : it works on a hot dog - being held by a finger
> .. but not on a hot dog that is not held by a finger !
Capacitance.
Better explanation than I can type:
http://machinedesign.com/guest-commentary/capacitance-system-stops-table-saws-amputating-fingers
--
eWoodShop: www.eWoodShop.com
Wood Shop: www.e-WoodShop.net
https://www.google.com/+eWoodShop
https://plus.google.com/+KarlCaillouet/posts
http://www.custommade.com/by/ewoodshop/
KarlCaillouet@ (the obvious)
Bill <[email protected]> wrote:
> Bill wrote:
>> Lew Hodgett wrote:
>>> Capacitance technology is older than dirt.
>>>
>>>
>>
>> Probably fewer than 1 in 10 have a clue, though I think the mF part > would catch on fast.
>>
> Please excuse my poor attempt at humor.
> Ya'll provided very good examples.
Nice edit on the MF. ;)
--
www.ewoodshop.com (Mobile)
[email protected] wrote:
>>>> I saw a demonstration - and cannot figure out why :
>>>> : it works on a finger
>>>> : it works on a hot dog - being held by a finger
>>>> .. but not on a hot dog that is not held by a finger !
-------------------------------------------------------------
"Bill" wrote:
> Maybe you should describe your knowledge about electricity and
> electronics first. Understanding this is not as
> simple as eating a hotdog. You may need to brush up before you
> properly approach the question.
--------------------------------------------------------------------------
Capacitance technology is older than dirt.
Most capacitance probes are found in level measurements in
process vessels.
Over the years I nave probably sold 1,000+ probes that have involved
either continuous level measurements in vessels that contained
conductive or non-conductive contents.
The same is true of point level devices (Saw-Stop is a point level
device).
Again the probe can be engineered to monitor either conductive
or non-conductive materials.
The vessel can be either conductive or non-conductive.
I've sold probes to operate at temperatures of 1,000F.
Although the science of capacitance probes is rather straight
forward and well documented, the real work is the application
engineering required to properly define the design of the probe
such that the probe solves the problem at hand.
I was fortunate to have a great application engineer,
but father time punched his ticket a couple of years ago,
far ahead of his time, but that is life.
As Bill has suggested, getting involved in an in depth discussion
of Saw-Stop technology is a little more complex than one might think.
Lew
Leon <lcb11211@swbelldotnet> wrote:
> On 8/19/2014 8:05 PM, Swingman wrote:
>> On 8/19/2014 7:04 PM, [email protected] wrote:
>>
>>> It was explained in the seminar < but not demonstrated > that
>>> if you fed a hotdog into the blade - but not holding it in your hand -
>>> - ie just having the hotdog held between 2 pieces of wood -
>>> the sawstop would not function to stop the blade ...
>>> it would cut the hotdog !
>>> That's what I couldn't understand.
>>> That's what I need to have explained.
>>
>> Capacitance is the ability to store an electrical charge (your body has
>> capacitance).
>>
>> There must also be a conductor to allow that electrical charge to flow
>> (or show a difference in potential) along a certain path (to the
>> mechanism of the sawstop).
>>
>> Wood, is not a good conductor (unless wet) of electricity, nor does it
>> have sufficient capacitance to store enough of charge on it own.
>>
>> Therefore the hot dog, when affixed between two pieces of wood (having
>> no, or a very week, electrical charge; and not being a good conductor)
>> will likely not create the difference/electrical flow necessary to trip
>> the sawstop circuit.
>>
>> That's a pretty simplistic explanation, and it has been a long time ...
>>
>
> And to just throw a wrench in the equation, the saw stop has an override
> switch for cutting wet lumber and or ferrous materials.
>
> My experience with cutting damp PT lumber is that the brake does not trip
> but does shut down the saw. So this probably backs up what Doug was
> indicating. The wet wood does not have enough capacity to store an
> electrical charge to trip the brake but apparently enough to shut down the saw.
Doug's correct in the human body being the source of capacitance sufficient
for the mechanism's sensors to detect the necessary difference to operate.
The moisture in the wood is what is allowing the detection of a difference
in the capacitance from your body to the mechanism's sensors, not that it
is storing an electrical charge. IOW, the moisture in the wood is providing
the path. (Perhaps enhanced by the chemicals used to treat it.)
For the OP's benefit, here is simple way to illustrate what I was trying
(poorly) to describe in response to his request for a _simple_ explanation
of the basic principle.
Take an iPad or any device that uses a capacitance touch screen.
Tightly roll/fold a _dry_ paper towel to thickness of a pencil. Which would
be the wood, holding the hot dog, in the OP's question.
Holding it in your bare fingers, try to use it as a stylus on your touch
screen. No dice.
Wet the paper towel "stylus", squeeze the water so that it is not
saturated, but moist, grasp it between your bare fingers, and stylus away.
The water has provided a path from your fingers, through the wet "wood", to
allow the capacitance screen's sensors to detect the difference required to
operate.
If you now wrap that wet stylus in sufficient dry paper that your fingers
are no longer be in contact with moisture (the hot dog held by wood,
instead of fingers in the OP's demo), the stylus will no longer work
Not exactly the same as the Sawstop, but a simple way to observe part of
the underlying principle the OP requested.
(Theoretically you can do the same thing by grounding both the device and
the stylus to the same plane)
--
www.ewoodshop.com (Mobile)
On 8/19/2014 7:04 PM, [email protected] wrote:
> It was explained in the seminar < but not demonstrated > that
> if you fed a hotdog into the blade - but not holding it in your hand -
> - ie just having the hotdog held between 2 pieces of wood -
> the sawstop would not function to stop the blade ...
> it would cut the hotdog !
> That's what I couldn't understand.
> That's what I need to have explained.
Capacitance is the ability to store an electrical charge (your body has
capacitance).
There must also be a conductor to allow that electrical charge to flow
(or show a difference in potential) along a certain path (to the
mechanism of the sawstop).
Wood, is not a good conductor (unless wet) of electricity, nor does it
have sufficient capacitance to store enough of charge on it own.
Therefore the hot dog, when affixed between two pieces of wood (having
no, or a very week, electrical charge; and not being a good conductor)
will likely not create the difference/electrical flow necessary to trip
the sawstop circuit.
That's a pretty simplistic explanation, and it has been a long time ...
--
eWoodShop: www.eWoodShop.com
Wood Shop: www.e-WoodShop.net
https://www.google.com/+eWoodShop
https://plus.google.com/+KarlCaillouet/posts
http://www.custommade.com/by/ewoodshop/
KarlCaillouet@ (the obvious)
[email protected] wrote:
> < snips>
>
>>
>>A capacitor "absorbs" and stores electricity up to its capacity, then
>>releases any addition electricity sent its way. A hotdog, although having
>>similar capacitance characteristics, is only a small mass, and capacitance
>>of human flesh (and hotdogs) functions as a relationship of mass to
>>capacitance content, or think of it as volume. If a human is holding the
>>hotdog, then the hotdog and the human essentially become one and there is
>>enough mass and capacitance "volume" that the saw can sense the change and
>>trigger the Sawstop. The hotdog held by sticks just does not have enough
>>mass and capacitance "volume" for the Sawstop to recognize the change.
>>
>>Does that get you to the answer?
>
>
> That one works best for me !
> Thanks Jim& everyone else who replied.
> John T.
>
>
> --- news://freenews.netfront.net/ - complaints: [email protected] ---
Does your computer have a touchpad? Move the cursor with your finger
on the touchpad. Then try it using a piece of plastic or wood. Low
capacitance and it doesn't work. Try it with a hotdog held between
two pieces of wood. It may or may not work, depending on the
sensitivity for capacitance of your touchpad. Same principle.
--
GW Ross
When the going gets tough, everybody
leaves.
[email protected] wrote in news:[email protected]:
> Hi all ;
>
> Can anyone provide a <somewhat > scientific .. yet
> <simple> explanation - of how the saw-stop
> _detection_ works ?
> I saw a demonstration - and cannot figure out why :
> : it works on a finger
> : it works on a hot dog - being held by a finger
> .. but not on a hot dog that is not held by a finger !
>
> I'm really missing something - and it's driving me crazy !
http://en.wikipedia.org/wiki/SawStop
[email protected] wrote in news:gpo7v9peibpve3l21bidlos50v750iga8r@
4ax.com:
> I guess that is what I need to have explained ...
> Thanks for the web links everyone - but none of them explain -
> - to me - how a finger stops the saw .. but a hotdog that is not
> held by a finger does not stop the saw ?
> Anyone have any idea ?
As has already been pointed out, SawStop uses an electronic circuit to determine the
capacitance -- the ability to store electric charge -- of the material being cut.
Surely it is obvious that an 80kg human body has a far greater ability to store electric
charge than a 50g hotdog. Their compositions are similiar, after all, and one would expect
that 1600x the mass would probably have a subtantial effect on capacitance.
Hence the circuit might be expected to react similarly to 80kg of human, and 80.05kg of
human + hotdog -- but quite differently to 50g of hotdog alone.
Of course, you could always email the manufacturer and get the information direct from the
authoritative source.
In rec.woodworking, <[email protected]> wrote:
> Can anyone provide a <somewhat > scientific .. yet
> <simple> explanation - of how the saw-stop
> _detection_ works ?
https://en.wikipedia.org/wiki/SawStop
SawStop's saws apply a small amount of electric voltage to the blade
of the saw. The current through the blade is continuously monitored.
If the saw detects a change in this current (as would occur if a
hand or other body part came into contact with the blade) an
automatic braking system is activated, forcing an aluminum brake
block into the blade. The saw stops within five milliseconds, and
angular momentum lowers the blade into the table. The operator
suffers a small nick instead of an amputation or other more serious
injury.[2] The design takes advantage of the difference in
"electrical conductivity" (similar to a GFI circuit) between wood
and flesh.[3]
Elijah
------
the dastardly movie villians need to use older saws now
On 8/19/2014 8:05 PM, Swingman wrote:
> On 8/19/2014 7:04 PM, [email protected] wrote:
>
>> It was explained in the seminar < but not demonstrated > that
>> if you fed a hotdog into the blade - but not holding it in your hand -
>> - ie just having the hotdog held between 2 pieces of wood -
>> the sawstop would not function to stop the blade ...
>> it would cut the hotdog !
>> That's what I couldn't understand.
>> That's what I need to have explained.
>
> Capacitance is the ability to store an electrical charge (your body has
> capacitance).
>
> There must also be a conductor to allow that electrical charge to flow
> (or show a difference in potential) along a certain path (to the
> mechanism of the sawstop).
>
> Wood, is not a good conductor (unless wet) of electricity, nor does it
> have sufficient capacitance to store enough of charge on it own.
>
> Therefore the hot dog, when affixed between two pieces of wood (having
> no, or a very week, electrical charge; and not being a good conductor)
> will likely not create the difference/electrical flow necessary to trip
> the sawstop circuit.
>
> That's a pretty simplistic explanation, and it has been a long time ...
>
And to just throw a wrench in the equation, the saw stop has an override
switch for cutting wet lumber and or ferrous materials.
My experience with cutting damp PT lumber is that the brake does not
trip but does shut down the saw. So this probably backs up what Doug
was indicating. The wet wood does not have enough capacity to store an
electrical charge to trip the brake but apparently enough to shut down
the saw.
On Tue, 19 Aug 2014 18:01:11 -0500, dpb <[email protected]> wrote:
>On 08/19/2014 5:13 PM, [email protected] wrote:
>...
>
>> I saw a demonstration - and cannot figure out why :
>> : it works on a finger
>> : it works on a hot dog - being held by a finger
>> .. but not on a hot dog that is not held by a finger !
>>
>...
>
>The demo's w/ the hotdog I've seen had it on a stick swinging into the
>blade...altho thinking about it, perhaps it was a metal rod so there was
>still a sizable object of capacitance in effect in contact...
>
>As the mechanical design article says, it's on the capacitance-matching;
>similar in principle to the capacitance-sensing lamp switching.
I guess that is what I need to have explained ...
Thanks for the web links everyone - but none of them explain -
- to me - how a finger stops the saw .. but a hotdog that is not
held by a finger does not stop the saw ?
Anyone have any idea ?
John T.
--- news://freenews.netfront.net/ - complaints: [email protected] ---
< snips >
>
>A capacitor "absorbs" and stores electricity up to its capacity, then
>releases any addition electricity sent its way. A hotdog, although having
>similar capacitance characteristics, is only a small mass, and capacitance
>of human flesh (and hotdogs) functions as a relationship of mass to
>capacitance content, or think of it as volume. If a human is holding the
>hotdog, then the hotdog and the human essentially become one and there is
>enough mass and capacitance "volume" that the saw can sense the change and
>trigger the Sawstop. The hotdog held by sticks just does not have enough
>mass and capacitance "volume" for the Sawstop to recognize the change.
>
>Does that get you to the answer?
That one works best for me !
Thanks Jim & everyone else who replied.
John T.
--- news://freenews.netfront.net/ - complaints: [email protected] ---
On 08/19/2014 5:13 PM, [email protected] wrote:
...
> I saw a demonstration - and cannot figure out why :
> : it works on a finger
> : it works on a hot dog - being held by a finger
> .. but not on a hot dog that is not held by a finger !
>
...
The demo's w/ the hotdog I've seen had it on a stick swinging into the
blade...altho thinking about it, perhaps it was a metal rod so there was
still a sizable object of capacitance in effect in contact...
As the mechanical design article says, it's on the capacitance-matching;
similar in principle to the capacitance-sensing lamp switching.
--
[email protected] wrote:
> Hi all ;
>
> Can anyone provide a <somewhat > scientific .. yet
> <simple> explanation - of how the saw-stop
> _detection_ works ?
> I saw a demonstration - and cannot figure out why :
> : it works on a finger
> : it works on a hot dog - being held by a finger
> .. but not on a hot dog that is not held by a finger !
>
> I'm really missing something - and it's driving me crazy !
>
> John T.
>
Not sure what you mean by not on a hot dog that is not held by a finger.
Have you really looked into this at all? Have you asked any questions of
the manufacturer?
--
-Mike-
[email protected]
[email protected] wrote:
> On Tue, 19 Aug 2014 19:50:41 -0400, "Mike Marlow"
> <[email protected]> wrote:
>
>> [email protected] wrote:
>>> Hi all ;
>>>
>>> Can anyone provide a <somewhat > scientific .. yet
>>> <simple> explanation - of how the saw-stop
>>> _detection_ works ?
>>> I saw a demonstration - and cannot figure out why :
>>> : it works on a finger
>>> : it works on a hot dog - being held by a finger
>>> .. but not on a hot dog that is not held by a finger !
>>>
>>> I'm really missing something - and it's driving me crazy !
>>>
>>> John T.
>>>
>>
>> Not sure what you mean by not on a hot dog that is not held by a
>> finger. Have you really looked into this at all? Have you asked any
>> questions of the manufacturer?
>
>
> It was explained in the seminar < but not demonstrated > that
> if you fed a hotdog into the blade - but not holding it in your hand -
> - ie just having the hotdog held between 2 pieces of wood -
> the sawstop would not function to stop the blade ...
> it would cut the hotdog !
> That's what I couldn't understand.
> That's what I need to have explained.
> Regards ;
> John T.
>
Very fair question but... have you posed your question to the manufacturer?
Do you really think you're likely to get the right answer in an internet
newsgroup?
--
-Mike-
[email protected]
[email protected] wrote:
> Question the manufacturer - not yet - the seminar was just today.
> Valuable info and answers from a usenet group ... you bet !
Often - yes. But if youv'e followed any form of newsgroup you surely will
know that you're not going to get the factual answers you want from usenet
newsgroups. But... go as you will, get as you do. Of course - don't bother
to ask the manufactuer... yet...
--
-Mike-
[email protected]
[email protected] wrote:
> On Tue, 19 Aug 2014 18:01:11 -0500, dpb <[email protected]> wrote:
>
>> On 08/19/2014 5:13 PM, [email protected] wrote:
>> ...
>>
>>> I saw a demonstration - and cannot figure out why :
>>> : it works on a finger
>>> : it works on a hot dog - being held by a finger
>>> .. but not on a hot dog that is not held by a finger !
>>>
>> ...
>>
>> The demo's w/ the hotdog I've seen had it on a stick swinging into the
>> blade...altho thinking about it, perhaps it was a metal rod so there was
>> still a sizable object of capacitance in effect in contact...
>>
>> As the mechanical design article says, it's on the capacitance-matching;
>> similar in principle to the capacitance-sensing lamp switching.
>
> I guess that is what I need to have explained ...
> Thanks for the web links everyone - but none of them explain -
> - to me - how a finger stops the saw .. but a hotdog that is not
> held by a finger does not stop the saw ?
> Anyone have any idea ?
> John T.
>
Maybe you should describe your knowledge about electricity and
electronics first. Understanding this is not as
simple as eating a hotdog. You may need to brush up before you properly
approach the question.
>
> --- news://freenews.netfront.net/ - complaints: [email protected] ---
<[email protected]> wrote in message
news:[email protected]...
> On Tue, 19 Aug 2014 19:50:41 -0400, "Mike Marlow"
> <[email protected]> wrote:
>
>>[email protected] wrote:
>>> Hi all ;
>>>
>>> Can anyone provide a <somewhat > scientific .. yet
>>> <simple> explanation - of how the saw-stop
>>> _detection_ works ?
>>> I saw a demonstration - and cannot figure out why :
>>> : it works on a finger
>>> : it works on a hot dog - being held by a finger
>>> .. but not on a hot dog that is not held by a finger !
>>>
>>> I'm really missing something - and it's driving me crazy !
>>>
>>> John T.
>>>
>>
>>Not sure what you mean by not on a hot dog that is not held by a finger.
>>Have you really looked into this at all? Have you asked any questions of
>>the manufacturer?
>
>
> It was explained in the seminar < but not demonstrated > that
> if you fed a hotdog into the blade - but not holding it in your hand -
> - ie just having the hotdog held between 2 pieces of wood -
> the sawstop would not function to stop the blade ...
> it would cut the hotdog !
> That's what I couldn't understand.
> That's what I need to have explained.
A capacitor "absorbs" and stores electricity up to its capacity, then
releases any addition electricity sent its way. A hotdog, although having
similar capacitance characteristics, is only a small mass, and capacitance
of human flesh (and hotdogs) functions as a relationship of mass to
capacitance content, or think of it as volume. If a human is holding the
hotdog, then the hotdog and the human essentially become one and there is
enough mass and capacitance "volume" that the saw can sense the change and
trigger the Sawstop. The hotdog held by sticks just does not have enough
mass and capacitance "volume" for the Sawstop to recognize the change.
Does that get you to the answer?
--
Jim in NC
---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com
Mike Marlow wrote:
> [email protected] wrote:
>
>> Question the manufacturer - not yet - the seminar was just today.
>> Valuable info and answers from a usenet group ... you bet !
>
> Often - yes. But if youv'e followed any form of newsgroup you surely
> will know that you're not going to get the factual answers you want
> from usenet newsgroups. But... go as you will, get as you do. Of
> course - don't bother to ask the manufactuer... yet...
I have a propensity for reading my own posts after the fact and realizing
that a previous post of mine came out harsher than I had wished it had -
sorry for that. Just wanted to encourage you to contact the manufacturer,
as it seems you are planning to do. There is some serious talent and
expertise in this group, so your outreach within this group is not in error,
but as one of our best (Karl - Swingman) is prone to say... within
newsgroups... free advice is often worth what you pay for it.
--
-Mike-
[email protected]
On Tue, 19 Aug 2014 22:52:35 +0000 (UTC), Eli the Bearded
<*@eli.users.panix.com> wrote:
>In rec.woodworking, <[email protected]> wrote:
>> Can anyone provide a <somewhat > scientific .. yet
>> <simple> explanation - of how the saw-stop
>> _detection_ works ?
>
>https://en.wikipedia.org/wiki/SawStop
>
> SawStop's saws apply a small amount of electric voltage to the blade
> of the saw. The current through the blade is continuously monitored.
> If the saw detects a change in this current (as would occur if a
> hand or other body part came into contact with the blade) an
> automatic braking system is activated, forcing an aluminum brake
> block into the blade. The saw stops within five milliseconds, and
> angular momentum lowers the blade into the table. The operator
> suffers a small nick instead of an amputation or other more serious
> injury.[2] The design takes advantage of the difference in
> "electrical conductivity" (similar to a GFI circuit) between wood
> and flesh.[3]
Not exactly electrical conductivity. Rather, as Swingman posted, it
detects the capacitance of the blade. If it touches your hand, the
capacitance will go up.
On Tue, 19 Aug 2014 19:50:41 -0400, "Mike Marlow"
<[email protected]> wrote:
>[email protected] wrote:
>> Hi all ;
>>
>> Can anyone provide a <somewhat > scientific .. yet
>> <simple> explanation - of how the saw-stop
>> _detection_ works ?
>> I saw a demonstration - and cannot figure out why :
>> : it works on a finger
>> : it works on a hot dog - being held by a finger
>> .. but not on a hot dog that is not held by a finger !
>>
>> I'm really missing something - and it's driving me crazy !
>>
>> John T.
>>
>
>Not sure what you mean by not on a hot dog that is not held by a finger.
>Have you really looked into this at all? Have you asked any questions of
>the manufacturer?
It was explained in the seminar < but not demonstrated > that
if you fed a hotdog into the blade - but not holding it in your hand -
- ie just having the hotdog held between 2 pieces of wood -
the sawstop would not function to stop the blade ...
it would cut the hotdog !
That's what I couldn't understand.
That's what I need to have explained.
Regards ;
John T.
--- news://freenews.netfront.net/ - complaints: [email protected] ---
On 8/20/2014 1:29 AM, Swingman wrote:
> Leon <lcb11211@swbelldotnet> wrote:
>> On 8/19/2014 8:05 PM, Swingman wrote:
>>> On 8/19/2014 7:04 PM, [email protected] wrote:
>>>
>>>> It was explained in the seminar < but not demonstrated > that
>>>> if you fed a hotdog into the blade - but not holding it in your hand -
>>>> - ie just having the hotdog held between 2 pieces of wood -
>>>> the sawstop would not function to stop the blade ...
>>>> it would cut the hotdog !
>>>> That's what I couldn't understand.
>>>> That's what I need to have explained.
>>>
>>> Capacitance is the ability to store an electrical charge (your body has
>>> capacitance).
>>>
>>> There must also be a conductor to allow that electrical charge to flow
>>> (or show a difference in potential) along a certain path (to the
>>> mechanism of the sawstop).
>>>
>>> Wood, is not a good conductor (unless wet) of electricity, nor does it
>>> have sufficient capacitance to store enough of charge on it own.
>>>
>>> Therefore the hot dog, when affixed between two pieces of wood (having
>>> no, or a very week, electrical charge; and not being a good conductor)
>>> will likely not create the difference/electrical flow necessary to trip
>>> the sawstop circuit.
>>>
>>> That's a pretty simplistic explanation, and it has been a long time ...
>>>
>>
>> And to just throw a wrench in the equation, the saw stop has an override
>> switch for cutting wet lumber and or ferrous materials.
>>
>> My experience with cutting damp PT lumber is that the brake does not trip
>> but does shut down the saw. So this probably backs up what Doug was
>> indicating. The wet wood does not have enough capacity to store an
>> electrical charge to trip the brake but apparently enough to shut down the saw.
>
> Doug's correct in the human body being the source of capacitance sufficient
> for the mechanism's sensors to detect the necessary difference to operate.
>
> The moisture in the wood is what is allowing the detection of a difference
> in the capacitance from your body to the mechanism's sensors, not that it
> is storing an electrical charge. IOW, the moisture in the wood is providing
> the path. (Perhaps enhanced by the chemicals used to treat it.)
Exactly however I assumed that any path at all was enough to trigger the
brake. I have been very careful,so far, to not cut into my aluminum
miter gauge fence, something that we all apparently do. ;~) My
assumption was that the wet wood would have the same effect as cutting
the fence while touching the fence with you hand or finger and or
cutting the hot dog while touching the dog with your hand or finger.
In the case of the wet wood there was no brake trip rather after cutting
a few inches the saw coasted to a stop repeatedly until I engaged the
over ride switch. So there must be some measure of the signal from the
blade to a conductive source that decides whether to brake or simply
shut down the saw.
Apparently the saw can detect the difference and for that matter I would
suspect that the saw top also has the ability to absorb the charge at
the blade.
>
> For the OP's benefit, here is simple way to illustrate what I was trying
> (poorly) to describe in response to his request for a _simple_ explanation
> of the basic principle.
>
> Take an iPad or any device that uses a capacitance touch screen.
>
> Tightly roll/fold a _dry_ paper towel to thickness of a pencil. Which would
> be the wood, holding the hot dog, in the OP's question.
>
> Holding it in your bare fingers, try to use it as a stylus on your touch
> screen. No dice.
>
> Wet the paper towel "stylus", squeeze the water so that it is not
> saturated, but moist, grasp it between your bare fingers, and stylus away.
>
> The water has provided a path from your fingers, through the wet "wood", to
> allow the capacitance screen's sensors to detect the difference required to
> operate.
>
> If you now wrap that wet stylus in sufficient dry paper that your fingers
> are no longer be in contact with moisture (the hot dog held by wood,
> instead of fingers in the OP's demo), the stylus will no longer work
>
> Not exactly the same as the Sawstop, but a simple way to observe part of
> the underlying principle the OP requested.
>
> (Theoretically you can do the same thing by grounding both the device and
> the stylus to the same plane)
>
>>>> Hi all ;
>>>>
>>>> Can anyone provide a <somewhat > scientific .. yet
>>>> <simple> explanation - of how the saw-stop
>>>> _detection_ works ?
>>>> I saw a demonstration - and cannot figure out why :
>>>> : it works on a finger
>>>> : it works on a hot dog - being held by a finger
>>>> .. but not on a hot dog that is not held by a finger !
>>>>
>>>> I'm really missing something - and it's driving me crazy !
>>>>
>>>> John T.
>>>>
>>>
>>> Not sure what you mean by not on a hot dog that is not held by a
>>> finger. Have you really looked into this at all? Have you asked any
>>> questions of the manufacturer?
>>
>>
>> It was explained in the seminar < but not demonstrated > that
>> if you fed a hotdog into the blade - but not holding it in your hand -
>> - ie just having the hotdog held between 2 pieces of wood -
>> the sawstop would not function to stop the blade ...
>> it would cut the hotdog !
>> That's what I couldn't understand.
>> That's what I need to have explained.
>> Regards ;
>> John T.
>>
>
>Very fair question but... have you posed your question to the manufacturer?
>Do you really think you're likely to get the right answer in an internet
>newsgroup?
Question the manufacturer - not yet - the seminar was just today.
Valuable info and answers from a usenet group ... you bet !
John T.
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