sawstop running

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Evidently the device does actually work. SawStop says that, during development, testing, and public demos, they have triggered the brake over a thousand times. One could discount that testimony as a magician endorsing their own parlor tricks. Maybe the SawStop employee doing each demo nudged a switch with his foot as he was feeding the plywood and hotdog through the blade. I guess that's why Fine Woodworking ran their tests - to make sure that SawStop wasn't tricking people. FWW concluded that the device is real and it works.
The device is fairly simple. Once you understand it, you might wonder why it hadn't been thought of sooner. They electrically isolate the blade, then feed a low voltage signal to it. They monitor the signal (about 3 volts). When the blade comes into contact with an object that has a lot of electrical capacitance, such as a human body, the signal voltage temporarily dips. This dip is much more pronounced when contacting a person than when cutting wood - unless you commonly rip pieces of wood that weigh 150 pounds, are at 80% moisture content, and have large unbroken electrical pathways throughout similar to our blood vessels.
Once contact is sensed the brake cartridge sends an electrical pulse through a stainless steel wire that is holding a spring compressed. The released spring pushes an aluminum brake pawl into the backside of the spinning blade. The blade burys itself in the brake pawl. Much of its rotational momentum is transferred into downward force, much like a car with its motor racing being knocked off concrete blocks, and the blade drops below the table top. This dropping motion is allowed by a specially designed arbor block with a pivot and spring loaded retainer.
To put the saw back into service you work the joined blade/pawl off the arbor and mounting posts, install a new blade and brake cartridge, and snap the arbor block back up into position. There is no damage to the saw. SawStop says that many of their tests have been on a single saw, and it is still running normally and in adjustment.
The cabinet saw already released includes hardware to implement this concept that may be overengineered and too carefully built. They are very interested in having the device work properly. It will be interesting, though morbid, to hear the first reports of actual contact with operators in regular shop situations.
Hope This Helps,
Dave
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George,
You are correct. A more accurate statement would be that the saw blade has to make substantial electrical contact with the operator's body. That can be accomplished through contact with a very small cross section of the bloodstream or a larger skin area. The hotdog demo, for example, involves electrical connection through the wet dog and across the finger/dog contact patch to get to the operator's body.
My saw senses contact whenever I touch the blade while it is stopped. The brake doesn't go off, but the LED control panel flashes a warning and the saw will not fire up until contact has ceased for at least five seconds.
I have also (very carefully) touched the blade side while it was running in Bypass Mode. The control panel flashed the contact pattern, so I know that the brake would have released if I hadn't been in Bypass.
The brake isn't activated by a charge (explosive). They use a strong spring. Explosives would be difficult to ship, might not burn properly when aged, and wouldn't push after the initial burst. The spring is inexpensive, ages well, and continues to push the pawl into the blade to ensure successful braking. The wire that holds the spring compressed is stainless steel so it should age well. The cartridge includes a resistance heater to keep the wire and capacitor above 50 degrees F at all times - ensuring that the burn-through will happen properly when needed.
Take Care,
Dave
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On 12 Jan 2005 22:00:57 -0500, snipped-for-privacy@designstrategies-dot-net.no-spam.invalid (dwright) vaguely proposed a theory ......and in reply I say!:
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Wait! There's a Bypass mode? Operator controllable? Uhoh! Suit City here we come, I reckon.
"Should I run my sawstop in bypass mode?" will replace "should I have a blade guard installed?" ?
In a working situation, is there any _record/log_ kept of each incident, and the state of the Saw Stop?
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Old Nick wrote:

Not really, bypass mode is specifically for metals and green wood that would trigger the Sawstop otherwise.

--
--John
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Old Nick,
I have no idea how diy came up with that address for me. I didn't type it anywhere when signing up. It's just designstrategies.net.
You've got a good hunch there. They had to include a bypass mode, and I wouldn't be surprised if the first person who gets bitten while using that mode sues SawStop claiming that they weren't running in bypass.
I have discussed the technology and the resulting saw's engineering at length with Steve Gass, as part of deciding whether or not to get one so early, but didn't get around to asking if the cartridge holds a record of operating patterns. It tells you if contact is sensed while in Bypass...would be trivial for it to record that info.
Most of the saw's smarts are in the cartridge. That make upgrades easier. If you happen to have endured reading my review you might have noticed that my saw received such an upgrade after I noticed an operational irregularity. At some point someone's got to try hacking the cartridge.
Regards,
Dave
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On 13 Jan 2005 22:00:48 -0500, snipped-for-privacy@designstrategies-dot-net.no-spam.invalid (dwright) vaguely proposed a theory ......and in reply I say!:
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Well it sounds as if somebody cares about your bum for you. Anti-spam addresses on the newsgroup are very common, to stop....well...spammers <G>. Hence my little request to remove ns when replying by email.

I remain neutral about SawStop. Which to say against, really, as I have not bought one <G>. But this one seems to be for _their_ protection.

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Kind'a like buying a "chip" to gain 30HP on your car, I suppose.
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You do know that that is how performance mods are legitimately done these days, right?
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What? My water injector and the little fans in the carb venturii are outdated?
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Well, water injection is also a legitimate technique - reduces combustion chamber temperature, and increases effective compression. A two-for-one effect in engines which can take advantage of it (turbo or super-charged, with engine management that can sense knock and adjust timing accordingly). Not sure about fans in the carb venturi, that sounds like a "magnets on the fuel line" kind of thing?
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Sure augmented thrust on our old turbojets when the water kicked in.
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Yup, it's real-world. Rolls-Royce was using it in aircraft engines at least as far back as WWII. I imagine it works in similar ways in a turbine engine (higher compression and able to burn more fuel cooler)?
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Oh yea - Bypass Mode is a little irritating to engage. They did that to discourage its regular use. You have to hold a key turned for at least a second while starting the saw.
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On 13 Jan 2005 23:00:58 -0500, snipped-for-privacy@designstrategies-dot-net.no-spam.invalid (dwright) vaguely proposed a theory ......and in reply I say!:
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But it will be done...<G>
Seriously, I am surprised they included it. Even after readin your other post.
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Old Nick wrote:

If they didn't then a lot of people would need two saws, one with Sawstop and one without.
--
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On Fri, 14 Jan 2005 05:29:59 -0500, "J. Clarke"
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Oh I can see the need! I just feel it will _legally_ negate the whole thing somewhere down the track, unless they cover their arses very carefully.
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duct tape
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Charles Spitzer wrote:

But does the key also have to be released in order to engage it?
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On Fri, 14 Jan 2005 11:28:28 -0700, "Charles Spitzer"
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Like I said...it will be done! <G>
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Ha! It may not work. The switch is a momentary contact keyswitch and it would have been easy for SawStop to program the routine so that it must start open, be held closed for 1 to 2 seconds, and go back open or else the saw won't run. I don't know that they did that though. I might give it a try for the heck of it next time I'm out in the shop.
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