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An alternative to Saw Stop?

by runswithscissors
posted 01-22-2013 07:37 AM


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232 replies

232 replies so far

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runswithscissors

1243 posts in 778 days


#1 posted 01-22-2013 07:46 AM

An update: Thinking continues to evolve. My Unisaw arbor pivots from the front, or near side of the table. If the arbor pivoted from the rear, or far side, of the table, the belts from the motor would tend to pull it down (not depending just on gravity). The switch should cut the motor at the same instant, to save belts from damage when they go slack (not actually sure whether that would be a problem). I’m not having any insight as to how the riving knife would work into this.

Another way that would allow the riving knife (which is the way at least one of Grizzly’s models works) is to simply drop the arbor straight down, rather than pivoting it down. But I do think the blade would get out of there most quickly by pivoting from the rear, pulled down by gravity and the drive belts simultaneously. I bet this could be made to be very quick acting. Dare I say it? Maybe even faster than the Saw Stop?

I’m trying to picture it: your finger (or hotdog) accidentally touches the blade, and POOF, it disappears beneath the ZCI. No damage done. You turn off the saw, press a button to reset the mechanism, crank up the arbor, and you’re in business again. Seems like it could work with dadoes as well.

It would be nice to hear other approaches, objections, caveats, etc. I know that this is the kind of topic that can bring out the best (and the worst) in woodworkers.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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Earlextech

1024 posts in 1443 days


#2 posted 01-22-2013 01:56 PM

I like it runswithscissors, this is the American spirit we love, create something yourself instead of complaining about what someone else is doing. Go for it!

-- Sam Hamory - The project is never finished until its "finished"!

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SamuraiSaw

489 posts in 717 days


#3 posted 01-22-2013 02:49 PM

I’ve only briefly looked at a Saw Stop, so help me understand the process. I know a sacrificial block slams into the blade, but what causes the arbor assembly to drop? Is that a mechanical process or is there another piece that has to be replaced?

I wonder what might be a problem with leaving the blade spinning….......................

I hope this remains a discussion and not a pissin’ match.

-- Artisan Woodworks of Texas.... www.awwtx.com

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Cosmicsniper

2199 posts in 1911 days


#4 posted 01-22-2013 02:56 PM

It drops because the energy from the spinning blade has to go somewhere even after stopping it. It’s own inertia carries it below the table.

-- jay, www.allaboutastro.com

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JesseTutt

811 posts in 863 days


#5 posted 01-22-2013 02:56 PM

My Grizzly bandsaw has a motor break that stops the blade within 3 seconds. If that was also added (to the arbor) it could help stop the blade. I know that 3 seconds is a long time in an accident, but a motor brake, arbor brake and dropping the arbor would provide 3 points of safety.

I thought I heard somewhere that the guy who invented the stop saw method had a umbrella patent that would cover any emergency stop / safety mechanism.

From Jay’s comment I assume there is a quick way to disengage the raise / lower blade mechanism.

-- Jesse, Saint Louis, Missouri

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ChuckV

2487 posts in 2280 days


#6 posted 01-22-2013 03:03 PM

I thought I heard somewhere that the guy who invented the stop saw method had a umbrella patent that would cover any emergency stop / safety mechanism.

Yes indeed. I received a letter from an attorney representing Saw Stop telling me that I have to stop hitting the off switch on my saw with my hip!

-- “While the world with closed eyes sleeps, The sky knows and weeps - steel rain. ” ― Nathan Bell

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SamuraiSaw

489 posts in 717 days


#7 posted 01-22-2013 03:13 PM

What releases the arbor allowing it to drop and how is that reset?

Please forgive my ignorance, but I’ve really not paid much attention to Saw Stop before now.

-- Artisan Woodworks of Texas.... www.awwtx.com

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helluvawreck

16043 posts in 1619 days


#8 posted 01-22-2013 03:15 PM

I am seriously thinking about getting a sawstop. At 62 I’ve been using table saws since high school but have never had an accident that injured me. However, I’m not getting any younger and I’m sure my concentration is not what it used to be. So…....

helluvawreck aka Charles
http://woodworkingexpo.wordpress.com

-- If a man does not keep pace with his companions, perhaps it is because he hears a different drummer. Let him step to the music which he hears, however measured or far away. Henry David Thoreau

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crank49

3524 posts in 1724 days


#9 posted 01-22-2013 04:23 PM

The Saw Stop patent would not stop you from making some other brake or drop and release method, but the SS method is absolutely the best one possible. Anything else will be second best.

I say that, not because I own one (I do not) or have any association with SS what so ever, just an observation of an engineer with 42 years of experience coming up with “outside the box” solutions to problems.

There are 2 main things about SS that make this design the best.
1- The brake cartridge stop block jams into the blade and stops it instantly. So fast that the motor and belts and even the arbor continue to rotate for a few milliseconds. It’s much harder to stop the mass of the motor than the relatively light blade in comparison.
2- The stop block jams into the back side of the blade so, due to the direction of rotation, the blade snatches itself below the table. There are no other energy sources needed because the blade rotation is directly converted into vertical movement in one direction (down).

These elements are what is protected by the patent because they are the essence of the design and the idea that created Saw Stop in the first place. This is what patents are for.

The flesh sensing technology is not unique. The touch screen on smart phones is similar technology.

If I were going to develop an alternate solution I would still grab the blade. There is no other way to stop something moving at ~200 feet per second, which is the tip speed of the teeth on a 10” blade spinning at 4500 RPM. But you would have to grab the sides of the blade, like a disk brake rotor to avoid the Saw Stop patent. Further, this brake caliper type devise would have to have some energy source.

Then I think a drive with a clutch that could disengage from the motor and engage a gear or cable to pull the blade below the table at the same time might be possible without infringing the patent.

Finally, even if this system could be made to work and not get into a patent piss fight with Saw Stop, it would surely cost more to produce and would not work quite as well. Not a system likely to be a market success.

-- Michael :-{| “If you tell a big enough lie and tell it frequently enough, it will be believed.” ― A H

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Underdog

556 posts in 788 days


#10 posted 01-22-2013 04:36 PM

The Whirlwind CEO has a couple prototypes of a system which seems to be an electronic brake that is activated if you touch the blade guard. So basically it doesn’t have to be as fast, because it’s more a preventative thing.

It doesn’t ruin a cartridge or a blade though.

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a1Jim

112936 posts in 2330 days


#11 posted 01-22-2013 04:53 PM

Saw stop does drop and stop when triggered. If just dropping the blade would work to protect your hands don’t you think they would have just done that?

-- http://artisticwoodstudio.com Custom furniture

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Jorge G.

1526 posts in 1228 days


#12 posted 01-22-2013 04:54 PM

Samurai and crank49 have it right, the kinetic energy of the blade has to go somewhere once the break engages. SS cleverly uses this energy to retract the blade.

Any alternative technology would have to preclude engaging the teeth of the blade to stop it, as I am sure Gass has completely covered this in his patent. Remember the guy is a patent lawyer and a PhD in physics, he is not stupid whatever else you think of him.

Having said that, we all know how the disc breaks in a car work. I am not an engineer so I don’t know how difficult this would be, but why not design something that acts like the breaks on a car, after all what we have is a spinning disc, just like in a car. Giving that the mass of a disc is so small I am sure break pads would be able to stop it pretty quick.

Carry on….this is my contribution. If you use my idea and invent one, you have to promise to sell it in Mexico… :-)

-- To surrender a dream leaves life as it is — and not as it could be.

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jmartel

2817 posts in 903 days


#13 posted 01-22-2013 07:51 PM

The problem with the brake pad design is that it doesn’t stop it nearly as fast. You would need to have it trigger BEFORE any skin touches the blade via proximity sensor. If you wait until your finger touches the blade, the blade would probably get halfway through your finger before it stops. Stopping it “pretty quick” won’t work. It needs to be almost instantaneous. The best way to do that is to jam something into the teeth (like sticking a stick through the spokes of a bicycle) like the SS does.

If you could develop a proximity sensor that would sense anything that’s roughly in the neighborhood of the blade insert and make it reusable, then it would work. Keep in mind though that if you get kickback and your hand gets thrown into the blade, it still may not activate in time.

-- End grain is like a belly button. Yes, I know you have one. No, I don't want to see it.

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Jorge G.

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#14 posted 01-22-2013 08:55 PM

You are assuming the break pad won’t work fast enough because you are comparing to a car, I think it would be a matter of testing. Remember, mass has a lot to do with this, I am sure the clamping pressure could be achieved to trigger the pads and break the disk in fractions of a second, just like SS.

-- To surrender a dream leaves life as it is — and not as it could be.

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Cosmicsniper

2199 posts in 1911 days


#15 posted 01-22-2013 09:02 PM

Especially if the break pad engages on both sides.

-- jay, www.allaboutastro.com

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Marcus

1081 posts in 772 days


#16 posted 01-22-2013 09:08 PM

I think there is already a proximity sensing disk break method out there….check out http://www.whirlwindtool.com/

They stop the blade in 1/8’s of a second. That is great for the situations they’re showing, but you would still be in pretty bad shape if kickback tossed you into the blade or the like. Granted, much better shape than you would be in without the device installed.

I have to agree with Michael…I think SawStop just got this idea right. They’ve been around for 10 yrs or so and there really isnt much for alternatives out there. I find it hard to believe that the big boys of the tool world (Delta, Powermatic and the like) didn’t work out a licensing agreement with them 10 yrs ago.

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RonInOhio

720 posts in 1617 days


#17 posted 01-22-2013 09:08 PM

I agree with JMartel. A proximity sensor seems to be more practible than a flesh sensing blade brake. Say if flesh gets to within a inch or two from the blade some built-in mechanism could do one of several things.

Sound a warning or flashing light and/or brake the blade. Of course the warning would have to not startle the
user of the saw.

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joeyinsouthaustin

1286 posts in 825 days


#18 posted 01-22-2013 09:31 PM

It seems that If stopping the inertia of the motor is harder than the blade, the way around the ss patent is to stop the motor rather than the blade. This might end up being more expensive, but what if a clutch disengaged the motor, a pancake brake stops the blade, and a solenoid or other drops it. With the motor disengaged it can run down on it’s own, the brake may not destroy the blade, and the solenoid or other could be repeatable. This would prolly be enough changes to defeat the patent???

However the best thing is just don’t let your hand get to the blade, this is possible with good technique.

-- Who is John Galt?

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RonInOhio

720 posts in 1617 days


#19 posted 01-22-2013 09:36 PM

The clutch is a decent idea but as you say. It definitely adds to the complexity and
cost.

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runswithscissors

1243 posts in 778 days


#20 posted 01-22-2013 10:01 PM

My thought is that the instant dropping of the blade makes stopping the blade less essential; in fact, if it could be done without messing up drive belts, etc., maybe it wouldn’t need to be stopped at all. The spinning blade, below the table, can’t injure you.

I like the idea of the solenoid. In fact, maybe the solenoid would hold the swing arm in position until triggered, at which point it would release it so it could drop. How about 2 solenoids, the second one to yank it down?

I’m not thinking of the blade dropping mechanism as being the same as the blade raising/lowering arbor mechanism. It would have its own separate pivot point. Needs to be very precise and robust, because you don’t want blade wobble and flutter.

I am not a patent attorney. But some years ago I had an idea or two that I thought were patentable. I researched all I could, and concluded that (1)patents are expensive (more than I was willing to invest) (2) easily evaded, by simply making various changes to the protected technology. I also am deeply dubious about an “umbrella patent,” which seems to say. “I have a patent on things I haven’t even thought of yet.”

My understanding is that SawStop offered the technology to other companies, and that they didn’t bite. I’d be curious to know the history of that.

Here’s a question that intrigues me: Has anyone had the nerve to stick his finger into a spinning SawStop blade?
I’m not talking about a hot dog here, but real, personal flesh. Also, is it possible for a SS to draw blood, even minimally?

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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HorizontalMike

6968 posts in 1667 days


#21 posted 01-22-2013 10:16 PM

I keep thinking of using centripetal force developed by the motor that is transferred to the blade/wheel. What about adding a mass (TBD) to the axis of the motor that would then “store” x-amount of centripetal force, that could then be used to pull/push the blade below the table? The only restriction that I see at the moment would be the need to ‘slow start’ the motor so as to NOT overload and blow circuits, but once running, this centripetal force would actually work FOR the saw when cutting thick lumber and the like…

Still thinking… carry on…

-- HorizontalMike -- "Woodpeckers understand..."

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TheCook

39 posts in 873 days


#22 posted 01-22-2013 10:33 PM

Crazier in my mind than the lack of alternative blade stopping/shifting technologies is the complete lack of consumer level sliding table saws. The whole hand-jammed-in-blade thing isn’t an issue if you’re nowhere near the blade. Kickback also doesn’t come up if the workpiece is clamped down.

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jmartel

2817 posts in 903 days


#23 posted 01-22-2013 10:45 PM

Jorge, I realize that it would be significantly faster than locking up the brakes on a car, but it is still slower than a sawstop style brake. Physics rules all. That’s the need for the proximity sensor. I believe I read that the whirlwind has 3x the braking time as the SS, but the sensor they use can make up the difference by firing BEFORE the hand contacts the blade.

runswithscissors: Gass stuck his own hand into the sawstop for a Discovery Channel show. http://www.youtube.com/watch?v=eiYoBbEZwlk

-- End grain is like a belly button. Yes, I know you have one. No, I don't want to see it.

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Woodmaster1

541 posts in 1340 days


#24 posted 01-22-2013 10:50 PM

The best alternative to saw stop is to use the safety features of the table saw, no patent infringement involved.

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JesseTutt

811 posts in 863 days


#25 posted 01-22-2013 11:00 PM

A couple has commented that SS is the best design. Although I would agree that this is the current state of the industry, I don’t agree that the future will not bring a better design. Consider those who claimed that the horse drawn wagon was the best transportation device. (please don’t tell me I am missing apples and oranges. The concept of claiming that current technology is the best and nothing better will ever be developed is what I am talking about.)

-- Jesse, Saint Louis, Missouri

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Purrmaster

839 posts in 846 days


#26 posted 01-22-2013 11:13 PM

I (sort of) have an idea. My miter saw has an electric brake. When I let go of the trigger I don’t have to wait for the blade to spin down. The motor stops it. I’m assuming it does this by sticking the motor into reverse but I could easily be wrong.

The electric brake doesn’t stop the saw blade nearly as fast the saw stop. My miter saw would easily chop through my fingers before the blade stopped. But the electric brake is a convenience feature, not a safety feature.

Could an electric brake be built that could stop the blade as quickly as the SawStop does? My guess is probably not or it would have been done by now. The miter saw is driven directly by the motor. Table saws use belts and I’m not sure an electric brake can work with belts.

On a personal note: I am not taking any sides on the SawStop debate.

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pwalter

78 posts in 1337 days


#27 posted 01-22-2013 11:26 PM

I actually think a “brake caliper” design would work. I am actually an automotive tech, and with enough force, you can make a vehicles TIRES stop spinning almost instantly. BUT, I would still be half tempted to say that the blade would be ruined. The force and energy is turned into heat. That much heat on the blade would most likely ruin it. But then again, I am just a tech, far from an engineer.

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PittsburghTim

214 posts in 1075 days


#28 posted 01-22-2013 11:32 PM

Why not have a gear or teeth on the arbor, away from the blade. When flesh is sensed, it would stop the blade and use the arbors rotating energy to drive it below the table.

-- She asked me, "Who are you going to please with that?" I said, "Me."

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rkober

137 posts in 1045 days


#29 posted 01-22-2013 11:43 PM

Being a mechanical engineer and holding a patent I have comment on this thread. Firstly I commend thinking out of the box. However the patent very well could be a real issue if it’s written strong enough. Some early inventors are fortunate and have a broad concept patented which provides a lot of protection.

Mechanically you have to consider the energy evolved (as mentioned by others). Force equals mass times acceleration. Any of these processes, including SS, are not instantaneous but VERY fast (milliseconds). Therefore the acceleration is extreme. What I’m getting at is a brake or trigger to drop the blade must unload a tremendous amount of energy in a very short period of time. Personally I think SS is pretty ingenious but their source of energy comes with a price. This is not to say I’m a SS fan.

-- Ray - Spokane, WA - “Most people don’t recognize opportunity because it’s usually disguised as hard work.” - Unknown

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HorizontalMike

6968 posts in 1667 days


#30 posted 01-22-2013 11:44 PM

Contrary to the statement that GASS “stuck” his hand in a TS blade, pay attention. He very, very, very, slowly moved his finger forward NOWHERE NEAR the speed of a regular cut. The damn coward, IMO. If he TRULY believed in his system then test it under REAL world conditions…PERIOD. Nuff’ said…

-- HorizontalMike -- "Woodpeckers understand..."

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NormG

4544 posts in 1757 days


#31 posted 01-23-2013 12:14 AM

If I could afford any saw that had the technology to stop the blade, I would purchase the equipment

-- Norman

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Jorge G.

1526 posts in 1228 days


#32 posted 01-23-2013 12:14 AM

He very, very, very, slowly moved his finger forward NOWHERE NEAR the speed of a regular cut

No he did not, the film was made with high speed cameras, thus appearing as if he was moving his finger very slow. There was another version of the same film but not as close to the blade where he is seen moving the finger very fast.

-- To surrender a dream leaves life as it is — and not as it could be.

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joeyinsouthaustin

1286 posts in 825 days


#33 posted 01-23-2013 12:28 AM

johnathan I ALREADY HAVE A PATENT CEASE AND DESIST. And I already paid the lobbyist :)


The cook
right on right on. Technique and technology. Of course it doesn’t take long on expensive blades and not so expensive cartridges to afford a pro model.

pwalter this is why I describe a pancake break, not caliper. Imagine two blade stabilizers. The heat is applied over the a larger area, evenly, and also, just a thought, with the motor disengaged, does not have to be applied to the blade itself.

To all, the clutch and break parts are integral to sooo many machines prolly would not cost that much.

-- Who is John Galt?

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crank49

3524 posts in 1724 days


#34 posted 01-23-2013 01:52 AM

I don’t think some folks realize how fast the SS stops the blade.

I already pointed out that the blade surface is moving at close to 200 feet per second. That’s 136 MPH, by the way.
When the brake (and please stop spelling this break) engages the blade, its circumference moves less than 3/8 inch in a circular path before it is below the table.

If you had a brake that would stop the blade in 1 millisecond, 1/1000 of a second, the blade would travel 2.4 inches in a circular path. That’s about 6 teeth on an 80 tooth blade.

It would take hundreds of times more power to stop the motor than it does to stop the blade alone. Also, consider the fact that the blade motion has to stop virtually instantly what ever is doing the stoping. So, to stop the motor that fast I am pretty sure the motor would be destroyed the same as the blade.

I still think the best alternate for stopping/retracting the blade would be a clutch to release the motor and use the considerable energy of the still spinning motor to snatch the blade below the table while disk brake calipers grab the blade. But this will be more expensive than SS and will not work as well.

I will say that a slider or a power feeder that would keep your hands completely away from the blade is just as good of an approach as the SawStop.

And, a completely different type of saw might be designed to displace the table saw all together. Perhaps a band saw with a wide blade could be as good at through cuts. Still need something for non-through cuts, however.

-- Michael :-{| “If you tell a big enough lie and tell it frequently enough, it will be believed.” ― A H

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RonInOhio

720 posts in 1617 days


#35 posted 01-23-2013 02:00 AM

Its possible that laser cutters with built-in alignments and such will eventually
replace TSs. They already have these units but not sure what kind of hurdles
there are for these units making TSs obselete. If ever.

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cutworm

1068 posts in 1546 days


#36 posted 01-23-2013 02:22 AM

I still don’t see how you can get your finger under the blade guard. Guess I’m a dummy. I guess you could if you tried.

-- Steve - "Never Give Up"

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derosa

1557 posts in 1588 days


#37 posted 01-23-2013 03:18 AM

Contrary to the statement that GASS “stuck” his hand in a TS blade, pay attention. He very, very, very, slowly moved his finger forward NOWHERE NEAR the speed of a regular cut. The damn coward, IMO. If he TRULY believed in his system then test it under REAL world conditions…PERIOD. Nuff’ said…
Maybe for real world testing he used the kitten toss test. Toss a extra cute kitten at the blade simulating the speed of someone slipping into the blade. If kitten remains extra cute then the system works; if the kitten becomes un-cute then he needed to tweak the design. I understand that real sawstop owners still use this test to check the viability of the system on occasion.

It would be interesting to see just how fast a hydraulic caliper for a bicycle would stop a saw blade. Magura used to produce a caliper for rim brakes that could grab so fast and hard that they could crush rims. But even a bicycle disc brake is designed to stop a couple hundred pounds being leveraged by a large, heavy wheel. A piston design like the sawstop uses could be used to activate the hydraulics. As long as Gass didn’t invent the piston then its use to activate an already existing bicycle caliper should be distant enough from his metal brake to do the job. On the down side, I’m not certain the blade would survive this kind of system, I’ve seen rotors warp from squeezing too hard and fast and in this system the piston would be designed to apply more pressure then a normal person’s squeeze.

-- --Rev. Russ in NY-- A posse ad esse

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oldnovice

3872 posts in 2121 days


#38 posted 01-23-2013 04:06 AM

Solenoids typically operate at about 40 milliseconds with a load connected so a much “better” solenoid would be designed.

A proximity sensor would also detect the wood as it would need to be a capacitive sensor as opposed the ferrous/all metals or all materials (ultrasonic)!

If the blade guard had flesh sensing capability then it could be used to stop the blade and it would not need to be as fast as SS. Flesh sending technology has been around for decades (I designed my first one over 50 years ago) as it just uses the human body as a “switch” to close the circuit (a low current switch). However, there are some cuts that require removing the guard just as I am sure that there are instances where the SS needs to be disabled.

I also wonder how many LJs wear gloves while sawing lumber and does SS detect gloves? I think not, it would need to get to the flesh first!

-- "I never met a board I didn't like!"

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Rick M.

4509 posts in 1133 days


#39 posted 01-23-2013 05:46 AM

I still don’t see how you can get your finger under the blade guard.

Same way you get a piece of wood under the guard.

-- http://thewoodknack.blogspot.com/

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oldnovice

3872 posts in 2121 days


#40 posted 01-23-2013 08:07 AM

Way back on my first job we manufactured trip controls which are used on various pieces of industrial machinery like punch presses and/or hydraulic presses which are loaded and operated manually. To insure that the operator had both hands out of the way before the press is engaged the operator is required to push two buttons nearly simultaneously. The circuitry in these controls also disallows locking down either of the push buttons so the operator cannot fool the controls.

I wrote the above explanation to consider an alternative to SS technology, i.e. an extremely versitile stock holding/feeding system that requires two hands to operate and keep them out of the way of the blade! If both hands are not on the system the saw will not allow the stock to move and if a hand comes off during a cut, the blade is turned off, with some braking, but not as much as SS as it can be determined how fast a hand can move from one of the safe positions to the guard and blade.

A sliding table TS is very close to keeping the hands away so now all that is needed is the electronics!

-- "I never met a board I didn't like!"

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dpoisson

184 posts in 1667 days


#41 posted 01-23-2013 04:25 PM

What if you would wear special gloves that could easily be detected for proximity to the blade? Make them grippy on the outside to help when handling wood and help save us from those darn splinters too.

As for dropping the blade / stopping it. What if you found a way to make the blade rise as it spins? If you make it stop spinning, it would fall, add on top of that a braking mecanism (disc brakes?) of some sort.

Truth be told, I don’t own a TS yet. But is there a lot of heat generated right before a kickback as the wood is applying lateral force on the blade? Could perhaps devise something to prevent kickbacks by detecting differences in temperatures?

Just thinking out loud…probably all garbage. Maybe someone smarter can fix what I just said ;-)

-- http://picasaweb.google.ca/dpoisson

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Tedstor

1507 posts in 1386 days


#42 posted 01-23-2013 04:49 PM

I’m late to the party. Sorry if my thoughts have already been mentioned.

1- Brakes on a car don’t work instantaneously, because they have 4,000lbs of mass pushing the car/wheels forward. When I worked as an auto tech, I occasionally put cars on a lifts, put the car in gear, and rev’d the engine (for diagnostic purposes- please don’t try this at home:)). When the car (as a whole) is not in motion, the brakes stop the wheels damn-near instanly when applied with sufficient force.
I would think a 10” saw blade could be stopped even faster.

2-Would an electro-magnetic clutch/brake be a feasible alternative?

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Ripthorn

799 posts in 1738 days


#43 posted 01-23-2013 05:08 PM

I like the idea of having some sort of a small disc, probably on the opposite side of the drive pulley from the blade, that gets utilized for harnessing the centripetal energy. You could have some sort of a pin that gets shoved in, like a stick in bike spokes, when the trip mechanism activates. Additionally, a brake could be applied to that same disc. The disc would likely need to be replaced, but it could be a 5 or 10 dollar replaceable thing as opposed to a $100 blade.

The clutch idea is also a good one, and could be incorporated so that there are multiple points of safety. With all of this, you may still need some sort of “cartridge” or something.

Of course, since a solenoid takes relatively long to activate, you could have some sort of a small piston or hammer that exerts a downward force on the front of the arbor so that it forces the blade under the saw about the rear pivot point. This could make it so that you could just push a reset button, move the mechanism back in to place, and go your merry way.

Sure all of these ideas would take additional refining and work to get right, but there are some possibilities. And something is surely better than nothing.

-- Brian T. - Exact science is not an exact science

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Dave

120 posts in 1950 days


#44 posted 01-23-2013 06:02 PM

I love this thread! There are some creative folks here on Lumberjocks. In the interest of keeping everyone’s creative juices flowing, here’s my two cents. To keep fingers intact we need to stop the blade, keep it away from the fingers, or both. Stopping the blade takes the same amount of energy no matter how you do it. The sawstop uses up the energy by deforming its brake and retracting the blade, destroying it in the process.

One way to make stopping the blade take less energy is to disconnect the arbor from the motor (magnetic clutch, for example, like tedstor mentioned). Motors have a LOT of inertia and something called “back EMF” too that makes them want to keep turning. Disconnecting it means a brake takes a LOT less energy to stop the blade and creates a lot less heat.

I also like the idea of mounting something to the arbor for the brake to hit besides the blade itself like ripthorn suggested. If the brake released into, say, an arbor-mounted gear (or something similar but more substantial that would absorb the impact without breaking) it would stop the spinning blade AND retract it into the table. With the right design you might even be able to reset everything without replacing any parts (or destroying the blade).

Both ideas above could be combined with a drum or disc brake that helps slow down the blade, but you might not need it.

By the way, if we don’t destroy any parts the cost of a “false alarm” goes way down so a proximity sensor starts to look like a great idea. Creating a “safe zone” around the blade to trigger its retraction isn’t a big deal if all you need to do is reset a few things and get back to work. It also means you don’t have to stop the blade as fast.

By the way, a REALLY crazy idea would be to design a “smart blade” that turns its teeth around or retracts them when it senses flesh. That way you could use it on any saw. Just imagine how expensive it’d be to get THAT resharpened, LOL.

Anyway, I’m hoping to keep my fingers away from sharp fast-spinning objects regardless of what they’re connected to. You guys have put out some really creative ideas and I’m looking forward to seeing where this thread goes. If anybody pitches the ideas to Powermatic can you negotiate a good deal for all of us on their new saws?

-- "I'm not afraid of heights. I'm afraid of widths." - Steven Wright

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oldnovice

3872 posts in 2121 days


#45 posted 01-23-2013 07:49 PM

Back EMF is more of a factor in DC motors and it has little if any effect on keeping the motor turning as that is due to the physical size of the rotor. And, physical size of the rotor has a lot to do with the amount of HP that a motor can develop.

I once worked with a motor that had a hollow rotor core and because of that it could start, reach 10,000 RPM, and stop at a 1KHz rate. On a servo system these motors could stop almost instantly due to the braking provided by the servo system! The problem is that to get a motor/servo system with enough HP to run a TS would be expensive.

Perhaps a hybrid of the hollow core and HP is a possible solution!

A blade clutch could be a solution if the blade also had a brake. If the blade was cutting stock the resistance of that would be a near instant stop but is would depend a lot on the material being cut so a brake would be desirable to have a consistent stopping time.

There are still some problems with the clutch/brake system:
  1. A rotating clutch/brake would increase the inertia.
  2. In order to get the required response time out of these magnetic components they must either be very small or highly over driven, possibly to near the destruction point of these components, and small components may not be up to the task.

I hope that I am not being too much of a wet blanket; let me know when to stop!

-- "I never met a board I didn't like!"

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SCOTSMAN

5594 posts in 2338 days


#46 posted 01-23-2013 08:05 PM

You can actually use three phase technology to stop the blade instantly and I mean instantly! Using the phases to oppose each. other so one phase is pushing to go forward the other is trying to go backward and you get a stalling humming effect when neither goes anywhere.This can be used as an effective braking system to save fingers etc
,I see after I wrote this the last time someone (company) was working on it then nothing.
The saw stop is a poorly thought out unecessary technique which actually damages the mechanism and is expensive to replace. The method I talk about is well known and would be just as effective without the hassle and expense. Alistair

-- excuse my typing as I have a form of parkinsons disease

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ocwoodworker

204 posts in 1757 days


#47 posted 01-23-2013 08:07 PM

10 more years and then this whole thread is moot. The patent will have expired and all can use it. Let him have his hay-day for inventing it.

-- I'd like to believe Murphy's Law haunts my woodshop, because if it's Karma it would mean I had something to do with it. - K.R.

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derosa

1557 posts in 1588 days


#48 posted 01-23-2013 08:10 PM

Unless he gets the right to renew the patent. I’m betting he won’t let the patent die unless something better comes along.

-- --Rev. Russ in NY-- A posse ad esse

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Alexandre

1417 posts in 944 days


#49 posted 01-23-2013 08:49 PM

I think this could be safer than a sawstop:

-- My terrible signature...

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cutworm

1068 posts in 1546 days


#50 posted 01-23-2013 10:16 PM

I’m perfectly happy with and fully trust my blade guard.

-- Steve - "Never Give Up"

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