Motor Reversing

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On 10/10/10 10:34 PM, Josepi wrote:

I would prefer powered off/normal on, because the operator would get used to the blade always braking and in the case of a solenoid failure, the blade would not coast.
I would also think an assembly with wheels applying just a little pressure to the sides of the blade would make a decent passive system. It would be just enough pressure to slow down the blade in a second or two and not enough pressure for the motor to even register the resistance.
Think about how little pressure it takes with a scrap piece of wood to stop a coasting blade.
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-MIKE- wrote:

Isn't there an old Indian trick about a spinning piece of wood and starting a fire?
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I know of a fellow that worked on a vertical sliding saw professionally and stopped it with the side of his thumb, for years. One day he got a carbide blade installed and forgot.
The fire was in the last half of his thumb.
Watch your working habits. Environments change. You may too... in body shape.
trick about a spinning piece of wood and starting a fire?
-MIKE- wrote:

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On 10/11/10 7:11 AM, HeyBub wrote:

Point?
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-MIKE- wrote:

Everybody knows that, which is why I'm trying to explain. But everyone's alive except those who drowned in an adjacent bog.
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On 10/11/10 3:05 PM, HeyBub wrote:

Put down the pipe. :-p
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I would think that an emergency stop mechanism would be a whole different magnitude than a scheduled, everyday, stop.
For a finger saver an emergency stop mechanism would have to stop the blade in a few teeth passings. For everyday usage a couple dozen blade rotations would be OK too. These two situations would require different tactics.
A dynamic electronic brake could vary the intensity for the two different scenarios and we could add the caliper to the emerg stop. A caliper probably wouldn't last long in everyday usage and would need to be adjusted and/or replaced frequently.
I would prefer powered off/normal on, because the operator would get used to the blade always braking and in the case of a solenoid failure, the blade would not coast.
I would also think an assembly with wheels applying just a little pressure to the sides of the blade would make a decent passive system. It would be just enough pressure to slow down the blade in a second or two and not enough pressure for the motor to even register the resistance.
Think about how little pressure it takes with a scrap piece of wood to stop a coasting blade.
--

On 10/10/10 10:34 PM, Josepi wrote:
> For fast stops a powered brake on may be preferred to normally brake on
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Josepi wrote:

indeed...
SawStop is a few (10's of iirc) msec.
By several "tooth passings" a finger is already pretty well history...
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says...

Sawstop stops the blade in 1/200 of a second, according to their Web site. At 3450 RPM that means the blade stops in .29 revolution, which with a 60 tooth blade means that 17 teeth have had a shot at your finger.
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On 10/11/10 12:08 PM, J. Clarke wrote:

That may be true, but they still don't do any harm.
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17 teeth?
How fast can you push your finger?
That may be true, but they still don't do any harm.

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Have you seen the videos and live demonstration? It does no harm. They wouldn't be selling like hotcakes if their marketing strategy centered around "losing only a pint of blood, instead of a whole finger." Have you seen the video demonstrations? They've been done with lunch meat and human fingers.

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On 10/12/2010 11:04 AM, -MIKE- wrote:

And with a 60-tooth blade spinning at 3450 RPM, that's 3450 teeth spinning past every *second*. At that speed, coming to a dead stop after only 17 teeth have had a chance to cut anything is pretty damn good. Unless you're just flat-out careless or stupid (or both) and are wildly advancing your fingers towards the blade, 17 teeth are not going to do much damage. I could do much worse in the blink of an eye with a careless swipe of my pocketknife.
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On 10/12/10 11:21 AM, Steve Turner wrote:

I've seen a hotdog demonstration in which they *did* push the dog, on top of a piece of wood, into the blade as quick as the blade with receive it. It was much faster than anyone with any sense would advance any stock into a table saw. The dog had the tiniest little sliver of "skin" taken off. Had it been a finger, it would surely have bled a drop or two. But I've done much worse to my finger when a file slipped or I got a splinter.
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This was exactly my point.
The other thing, and unfair to the 17 teeth is OK defence is that the SawStop pulls the blade away and down. It appears to be grabbed on the back side of the blade and the inertia pulls the balde back and under the table effectively removing the blade from the finger area. I doubt you would want to do this everytime in a **NON**emergency stop. My guess is arbor bending would set in after a few dozen of them.
Watch the videos (most have). This is no gentle stop for an armature and saw blade of that intertia.
So the retort to the 17 teeth big damage people is still "How fast do you push your finger?"
OTOH: Pushing the stock, slipping off, and back handing a running blade can be different speeds.
I've seen a hotdog demonstration in which they *did* push the dog, on top of a piece of wood, into the blade as quick as the blade with receive it. It was much faster than anyone with any sense would advance any stock into a table saw. The dog had the tiniest little sliver of "skin" taken off. Had it been a finger, it would surely have bled a drop or two. But I've done much worse to my finger when a file slipped or I got a splinter.
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On 10/12/10 12:13 PM, Josepi wrote:

I guess I don't know what we're debating, anymore. I thought we were talking about slowing down the coast of a saw blade after turning off the power. I guess we got on a tangent.
If it's you're mission to dream up ways to refute the effectiveness of the SawStop technology... well, I'm off the boat, because you've lost your mind. :-)
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LOL..I guess I am in the same boat as you. I did jump in late and saw (pun) some twist about emerg. stopping the blade. Then I jumped in to point out a difference in technique would be needed and got some resistance. Now I am chatting with you and who knows whwre it went.
I am not disputing the effectiveness of the SawStop, at all. After seeing videos I feel I owe the guy something without buying one. Amazing design. Now I want to kno how to beat it with my wallet.
BTW: never owned a table saw and have never intended to. I know too many that have lost an eye, fingers, thumb pieces and a **dog to one. When I wave to somebody I don't want them to think I am giving them the one finger salute.
**(j/k about the dog...LOL)
I guess I don't know what we're debating, anymore. I thought we were talking about slowing down the coast of a saw blade after turning off the power. I guess we got on a tangent.
If it's you're mission to dream up ways to refute the effectiveness of the SawStop technology... well, I'm off the boat, because you've lost your mind. :-)
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wrote:
wildly advancing your fingers towards the blade,
As is done when, say, you are pushing a bit of wood into the saw and it jerks out of place and you essentially "fall" forward now that the wood is no longer offering resistance?
Of course, the blade never stop turning at all on the saw I was using, but I did manage to put three finges and a thumb in its path before realizing I was cutting skin and bone - and jerked back.
Only cut clean through one digit and got it sewed and screwed back on.
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On 10/12/2010 9:19 PM, Hoosierpopi wrote:

I've read that about five times and have tried to visualize what you're talking about, but I'm still puzzled.

Would I be correct in assuming you were pushing the wood into the blade with your bare hands rather than using a push jig or Gripper or something similar?
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I doubt most people use a pusher stick to cut plywood sheets.
Now we have to define "close"...LOL

I've read that about five times and have tried to visualize what you're talking about, but I'm still puzzled.

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