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#1
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SawStop science
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: --- |
#2
Posted to rec.woodworking
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SawStop science
In rec.woodworking, 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 |
#3
Posted to rec.woodworking
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SawStop science
On 8/19/2014 5:13 PM, 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-comme...tating-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) |
#6
Posted to rec.woodworking
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SawStop science
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- |
#7
Posted to rec.woodworking
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SawStop science
On Tue, 19 Aug 2014 18:01:11 -0500, dpb wrote:
On 08/19/2014 5:13 PM, 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: --- |
#8
Posted to rec.woodworking
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SawStop science
On Tue, 19 Aug 2014 19:50:41 -0400, "Mike Marlow"
wrote: 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: --- |
#9
Posted to rec.woodworking
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SawStop science
wrote:
On Tue, 19 Aug 2014 19:50:41 -0400, "Mike Marlow" wrote: 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- |
#10
Posted to rec.woodworking
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SawStop science
On Tue, 19 Aug 2014 22:52:35 +0000 (UTC), Eli the Bearded
wrote: In rec.woodworking, 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. |
#11
Posted to rec.woodworking
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SawStop science
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. --- news://freenews.netfront.net/ - complaints: --- |
#12
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SawStop science
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- |
#13
Posted to rec.woodworking
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SawStop science
On 8/19/2014 7:04 PM, 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) |
#14
Posted to rec.woodworking
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SawStop science
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#15
Posted to rec.woodworking
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SawStop science
wrote:
On Tue, 19 Aug 2014 18:01:11 -0500, dpb wrote: On 08/19/2014 5:13 PM, 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: --- |
#16
Posted to rec.woodworking
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Sawstop science
wrote in message ... On Tue, 19 Aug 2014 19:50:41 -0400, "Mike Marlow" wrote: 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 |
#17
Posted to rec.woodworking
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SawStop science
On 8/19/2014 8:05 PM, Swingman wrote:
On 8/19/2014 7:04 PM, 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. |
#18
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SawStop science
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#19
Posted to rec.woodworking
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SawStop science
Leon lcb11211@swbelldotnet wrote:
On 8/19/2014 8:05 PM, Swingman wrote: On 8/19/2014 7:04 PM, 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) |
#20
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SawStop science
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. |
#21
Posted to rec.woodworking
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SawStop science
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. |
#22
Posted to rec.woodworking
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SawStop science
Bill 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) |
#23
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SawStop science
Mike Marlow wrote:
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- |
#24
Posted to rec.woodworking
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Sawstop science
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: --- |
#25
Posted to rec.woodworking
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SawStop science
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, 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) |
#26
Posted to rec.woodworking
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Sawstop science
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: --- 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. |
#27
Posted to rec.woodworking
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SawStop science
Geez, I don't read the newsgroup for a few days, and look what happens... -- When the game is over, the pawn and the king are returned to the same box. Larry W. - Baltimore Maryland - lwasserm(a)sdf. lonestar.org |
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