Consumer Product Safety Comm. to discuss proposed SawStop technology safety rule

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Finding the keyboard operational George Max entered:

coffee spray!!! Seriously the product warning lables are getting ridiculous. And not just the badly translated. I groan inwardly every time I see "caution contents may be hot" on a lid. If it isn't hot, I'm out of business. So it is with SawStop. As I see it there are two types of tabesaw acccidents. Being careful operator with an Opps and the careless operator. Both need the protection. Having reread the SawStop web site, I am very concerned about a third kind of trigger. If SawStop works by sensing a electrcal signal, what happens if someone is using a motor with worn brushes in the area or an arc welder? I know (hope) it's been tested for this but you can't test for everything. Bob
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On Fri, 08 Sep 2006 17:55:27 GMT, "The Other Funk"

You're in the retail coffee business? Sorta like Starbucks?
Moving onto the saw - this is what UL attempts to do. Test for everything. They say it senses the capacitance of a human body. I wonder if the amount of that capacitance is the same from individual is the same, and if not, does that make a difference? The electronics of the device can probably be shielded from interference, but the blade is part of the circuit, I don't think that can be shielded and in fact may act as an antenna. I'm also wondering about those teflon coated blades, but that might not matter since the teeth won't have teflon on them.
Since this is probably a new category of device for UL, they're going to have to dream up tests for it. Assuming it's totally new or at least nothing very similar.
There's going to be a heck of a lot of investigation on this.
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Finding the keyboard operational George Max entered:

If you are going to start talking dirty like that, I'll give you decaf. But yes I am in the coffee business. Check out the link in my sig.

The capacitance of the the human body, as measured to the saw blade (or where ever they are measuring it) will vary but I am sure they can cover the range. It's probably cheaper and easier to cover a range then a single value. The SawStop site doesn't go into any detail but I would guess the blade is a major part of the sensing part. If I get a chance , I'll look up the patent(s) and see what I can learn. Bob
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That has been known to trigger it. Last I heard, if you have these problems, they will send you a filter.

I
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Finding the keyboard operational CW entered:

If a filter makes the device less sensitive, what is their legal exposure if that saw then bites someone?
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It doesn't make it less sensitive. It filters out the static and voltave spikes on the line that are causing misfires.

if
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Finding the keyboard operational CW entered:

Well I believe you but I am going to have to do some research of my own. I thought that the trigger was a voltage spike. I'll get back to you. Bob
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Capacitance change is the trigger. Likely somewhat more sophisticated but essentially like a touch lamp.
I

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Finding the keyboard operational CW entered:

I read it as a voltage spike caused by a change in capacitance. Guess I better read it again. Bob
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I wondered about this as well. I read an article on the net that said it senses a *change* between the wood and say a hand/finger. But what if the accident happened before or after cutting. For example, and illustrative purpose only, what if one was to stick their hand directly into the blade? This would not result in a change of any kind. I don't know much about electronics.
Anybody?

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There are a few methods of doing this but the simplest is to have a tuned circuit ballanced by a certain capacitance. Proximity or contact from a human being will change that capacitance, throwing the circuit out of balance and trigger an event. A piece of wood will not do this because it is an insulator. The circuit does not detect the difference between a piece of wood and you, it just doesn't detect the wood at all.

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On Sat, 09 Sep 2006 13:43:38 -0400, Joe Bemier

Yes it would. The wood, if it's dry, has little/no effect on the system because it is a poor conductor. You are a good conductor and you have an effect no matter what.
Think of it more like this, the blade is full of water. The wood is impermeable to water. The skin soaks it up like a dry sponge. When you run the wood through it nothing happens to the water in the blade. As soon as your sponge hits it the water gets soaked up. Even though water is constantly supplied to the blade, the amount of water in it momentarily drops because so much of it moved out suddenly.
-Leuf
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wrote:

Great analogy! It's a slick invention, no doubt. But, personally, I can't agree with the course of mandating the technology, unless it was at a price that did not make much difference, i.e., <$100 at retail.
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Finding the keyboard operational Joe Bemier entered:

Joe, we are going to see more and more SawStop equiped shops as the insurance industry forces it upon the commercial sector. Then the saw mfrs insurance companies will insist on it. It's going to be market driven not legislated. Which means that the price will be all the market an bear. Bob
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On Sun, 10 Sep 2006 01:18:27 GMT, "The Other Funk"

As much as it bothers me I believe you are right, Bob. Its progress, I guess.
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I don't want to fan the flames but this article has some interesting points http://www.edn.com/article/CA502427.html The add on price quoted here is $150.00 not the $400.00 that has been bandied about. Since the controller is a TI part, it can't be too hard to build a competing product. The big trick is stopping the blade. Bob
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And on that note, there are proven, old tech methods of stopping electric motors using brakes or electrical methods. Years ago I worked at a plant that had among other things a "two roll mill." Without getting too specific about it's operation, it was driven by a 150 HP motor, and the business end consisted of 2 steel rollers, each about 4 feet long & 2 feet in diameter, rotating next to each other with a pinch point of about 1/2" or so between them. I'd guess that each roller weighed a couple/few tons. The whole setup had a safety bar above it that activated a braking mechanism. It was SOP for the operator to use this when he wanted to stop the mill for any reason, not just in emergencies. It would stop the entire machine, motor, gearing, etc, in less than a 1/4 turn of the main rollers without any damage to the machine, and could be reset by the operator, and the machine restarted, in less than a minute. (IIRC the rollers turned in the neighborhood of 100 RPM)
For that matter, just think how fast the brake on a CMS or router stops the tool (admittedly their reliability factor is not that high!) I'm no engineer, but it sure seems to me that it would be possible to stop a TS without a one-time-use cartridge.
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Larry Wasserman Baltimore, Maryland
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The amount of time for a CMS to come to a stop is sufficient to amputate a finger. Yes, there are ways of stopping a motor quite quickly but, even a partial rotation could be disastrous. In any case, stopping it that quickly would almost certainly unscrew the blade nut. A freewheeling blade will cut quite nicely.
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I think your right Leon, it will be awhile I think before its big with the home consumer, but for shops the potential insurance savings and what OSHa may adopt for rules I think you'll eventually see a lot of it and expanded to other tools.
Mike M
On Wed, 06 Sep 2006 15:50:51 GMT, "Leon"

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Along those lines, Robin at Lee Valley admitted a few months back that they're swapping out regular saws for sawstops in all their facilities. The long and short of it is that it's just too costly not to adopt the technology.
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