Motor Reversing
HeyBub
"Single-phase induction motors drive many arbor-mounted cutting tools in the
home workshop. Stationary grinders, table and radial arm circular saws
frequently turn abrasive or cutting disks that are directly mounted on the
motor's spindle. These disks have large inertial moments that allow them to
free wheel for a long time after the power is turned off. A lengthy coast to
complete stop often amounts to a major inconvenience."
http://www.homemetalshopclub.org/news/sep01/sep01.html#reversing
EXT
"HeyBub" <hey...@NOSPAMgmail.com> wrote in message
news:4-idnf9GbsSMHTLR...@earthlink.com...
HeyBub
I was looking for a home remedy for a festering, fulminating, giant red mass
on my, er, never mind. Just say I stumbled across it and thought it might be
interesting to some (the motor business, not my, um, temporary disability).
WW
"HeyBub" <hey...@NOSPAMgmail.com> wrote in message
news:4-idnf9GbsSMHTLR...@earthlink.com...
>WW
Larry Jaques
wrote:
>In article <A7CdneSTh70fUTLR...@earthlink.com>,
> HeyBub <hey...@NOSPAMgmail.com> wrote:
>> I was looking for a home remedy for a festering, fulminating, giant red
>> mass on my, er, never mind.
>
>A boil on the bum then :-)
Sounded like election-time talk to me. <shrug>
--
Ask not what the world needs. Ask what makes you come
alive... then go do it. Because what the world needs
is people who have come alive. -- Howard Thurman
willshak
If I need to stop a spinning table saw blade in a hurry to change or
reset something, I find that a scrap piece of lumber makes a great blade
brake. Turn the saw off and slide the scrap up to the still spinning
blade. Blade stops in a couple of seconds. No extra parts needed.
--
Bill
In Hamptonburgh, NY
In the original Orange County. Est. 1683
To email, remove the double zeroes after @
-MIKE-
Someone could make some money by developing an aftermarket saw brake,
under the table.... pads or rollers or whatever, that would squeeze the
blade.
--
-MIKE-
"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com
mi...@mikedrumsDOT.com
---remove "DOT" ^^^^ to reply
Larry Jaques
wrote:
>On 10/10/10 11:35 AM, willshak wrote:
>> WW wrote the following:
>>> "HeyBub" <hey...@NOSPAMgmail.com> wrote in message
>>> news:4-idnf9GbsSMHTLR...@earthlink.com...
>>>> Found this article...
>>>>
>>>> "Single-phase induction motors drive many arbor-mounted cutting tools
>>>> in the home workshop. Stationary grinders, table and radial arm
>>>> circular saws frequently turn abrasive or cutting disks that are
>>>> directly mounted on the motor's spindle. These disks have large
>>>> inertial moments that allow them to free wheel for a long time after
>>>> the power is turned off. A lengthy coast to complete stop often
>>>> amounts to a major inconvenience."
>>>>
>>>> http://www.homemetalshopclub.org/news/sep01/sep01.html#reversing
>>>>
>>>>
>>>> Great ... I may rig up my table saw this way. Would be safer with a
>>>> brake. WW
>>
>> If I need to stop a spinning table saw blade in a hurry to change or
>> reset something, I find that a scrap piece of lumber makes a great blade
>> brake. Turn the saw off and slide the scrap up to the still spinning
>> blade. Blade stops in a couple of seconds. No extra parts needed.
>>
>
>Someone could make some money by developing an aftermarket saw brake,
>under the table.... pads or rollers or whatever, that would squeeze the
>blade.
Lawsuits from the arse with the SawStop patents notwithstanding, I
think he went with the positive stop style because it's the only one
which would keep from taking a finger off. The rest spin just enough
to do serious damage.
-MIKE-
A saw blade brake wouldn't infringe on SawStop's patent at all.
Steve Turner
> On 10/10/10 11:35 AM, willshak wrote:
>> WW wrote the following:
>>> "HeyBub" <hey...@NOSPAMgmail.com> wrote in message
>>> news:4-idnf9GbsSMHTLR...@earthlink.com...
>>>> Found this article...
>>>>
>>>> "Single-phase induction motors drive many arbor-mounted cutting tools
>>>> in the home workshop. Stationary grinders, table and radial arm
>>>> circular saws frequently turn abrasive or cutting disks that are
>>>> directly mounted on the motor's spindle. These disks have large
>>>> inertial moments that allow them to free wheel for a long time after
>>>> the power is turned off. A lengthy coast to complete stop often
>>>> amounts to a major inconvenience."
>>>>
>>>> http://www.homemetalshopclub.org/news/sep01/sep01.html#reversing
>>>>
>>>>
>>>> Great ... I may rig up my table saw this way. Would be safer with a
>>>> brake. WW
>>
>> If I need to stop a spinning table saw blade in a hurry to change or
>> reset something, I find that a scrap piece of lumber makes a great blade
>> brake. Turn the saw off and slide the scrap up to the still spinning
>> blade. Blade stops in a couple of seconds. No extra parts needed.
>>
>
> Someone could make some money by developing an aftermarket saw brake, under the
> table.... pads or rollers or whatever, that would squeeze the blade.
I've always wondered if a set of good quality bicycle brakes couldn't be safely
mounted on the trunnion to perform that very task. Route the cable to the
front of the saw to a hand or foot operated lever and there ya go.
--
Free bad advice available here.
To reply, eat the taco.
http://www.flickr.com/photos/bbqboyee/
Kerry Montgomery
"Steve Turner" <bbqb...@swtacobell.net.invalid> wrote in message
news:i8tn2l$1hv$1...@news.eternal-september.org...
The now common disk brakes might be a great match - their designed to grab a
thin metal disk instead of a wide rim.
Kerry
Larry Jaques
wrote:
WTF does that have to do with lawsuits? People sue to keep their
product on top whether they have a case or not. REAL WORLD, Mike.
-MIKE-
>> Someone could make some money by developing an aftermarket saw brake,
>> under the
>> table.... pads or rollers or whatever, that would squeeze the blade.
>
> I've always wondered if a set of good quality bicycle brakes couldn't be
> safely mounted on the trunnion to perform that very task. Route the
> cable to the front of the saw to a hand or foot operated lever and there
> ya go.
>
Interesting. There is certainly a lot for force against a bike brake
than a coasting saw blade/motor. I think a simple spring and
electromagnet/solenoid would do the trick in the same way an electric
door bell works.
No electric current: spring holds brakes closed.
Electric current: solenoid pulls brakes open.
A manual cable or secondary electric source could be added for manual
brake release.
-MIKE-
In the "REAL WORLD" (relax, man), patent infringement law suits get
thrown out in the first hearing, too, Larry. What, you're a patent
attorney, too?
Josepi
a spring setting the speed and strength to be held open all the time.
"-MIKE-" <mi...@mikedrumsDOT.com> wrote in message
news:i8tsnd$3us$1...@news.eternal-september.org...
-MIKE-
> For fast stops a powered brake on may be preferred to normally brake on with
> a spring setting the speed and strength to be held open all the time.
>
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.
J. Clarke
mi...@mikedrumsDOT.com says...
In any case, since EU law requires brakes already (indirectly, with an
allowed spindown time IIRC), Sawstop would have an uphill battle
claiming that they infringe its patents.
HeyBub
>
> 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.
Isn't there an old Indian trick about a spinning piece of wood and starting
a fire?
Larry Jaques
wrote:
No, I've just been horrified at how many frivolous lawsuits make it
into court, including patent infringement suits. Check it out.
Josepi
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.
"-MIKE-" <mi...@mikedrumsDOT.com> wrote in message
news:i8u31p$foe$1...@news.eternal-september.org...
Josepi
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.
"HeyBub" <hey...@NOSPAMgmail.com> wrote in message Isn't there an old Indian
trick about a spinning piece of wood and starting
a fire?
news:Po2dnYsq7ZB9Yy_R...@earthlink.com...
dpb
> I would think that an emergency stop mechanism would be a whole different
> magnitude than a scheduled, everyday, stop.
indeed...
> For a finger saver an emergency stop mechanism would have to stop the blade
> in a few teeth passings. ...
SawStop is a few (10's of iirc) msec.
By several "tooth passings" a finger is already pretty well history...
--
-MIKE-
Especially since it's apples and oranges.
SawStop is a safety brake that only stops when contact with flesh is
made, and it's instantaneous.
I'm talking about a gradual brake that occurs as part of normal operation.
-MIKE-
Point?
-MIKE-
> On Sun, 10 Oct 2010 21:41:24 -0500, -MIKE-<mi...@mikedrumsDOT.com>
> wrote:
>
>> On 10/10/10 9:22 PM, Larry Jaques wrote:
>
>>> WTF does that have to do with lawsuits? People sue to keep their
>>> product on top whether they have a case or not. REAL WORLD, Mike.
>>>
>>
>> In the "REAL WORLD" (relax, man), patent infringement law suits get
>> thrown out in the first hearing, too, Larry. What, you're a patent
>> attorney, too?
>
> No, I've just been horrified at how many frivolous lawsuits make it
> into court, including patent infringement suits. Check it out.
>
I understand and it is certainly frustrating.
But, if we let that deter us, not one would ever invent anything.
J. Clarke
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.
J. Clarke
>
> 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.
So how much power do you have to put into that electronic brake to stop
the blade as fast as Sawstop's physical block?
And why would a caliper not last long? A set of brake pads on a car
with 10" rotors lasts 40,000 miles or so, and they're getting a Hell of
a lot more of a workout that they would stopping a little bitty saw
blade that masses less than 1/1000 as much.
-MIKE-
That may be true, but they still don't do any harm.
HeyBub
> On 10/11/10 7:11 AM, HeyBub wrote:
>> -MIKE- 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.
>>
>> Isn't there an old Indian trick about a spinning piece of wood and
>> starting a fire?
>>
>
> Point?
Everybody knows that, which is why I'm trying to explain. But everyone's
alive except those who drowned in an adjacent bog.
-MIKE-
Put down the pipe. :-p
Bill
> In article<dsGso.3869$OB2....@newsfe02.iad>, JRM.@easynews.com says...
>>
>> 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.
>
> So how much power do you have to put into that electronic brake to stop
> the blade as fast as Sawstop's physical block?
>
> And why would a caliper not last long? A set of brake pads on a car
> with 10" rotors lasts 40,000 miles or so, and they're getting a Hell of
> a lot more of a workout that they would stopping a little bitty saw
> blade that masses less than 1/1000 as much.
The physics on that seem interesting. A little like stopping a speeding
bullet on a dime--it challenges my imagination. Probably not quite as
difficult as stopping a lightning bolt, but I wouldn't want to try that
either.
Bill
Josepi
17 teeth?
How fast can you push your finger?
"-MIKE-" <mi...@mikedrumsDOT.com> wrote in message
news:i8vkeg$te2$1...@news.eternal-september.org...
-MIKE-
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.
> 17 teeth?
>
> How fast can you push your finger?
>
> "-MIKE-"<mi...@mikedrumsDOT.com> wrote in message
>
Steve Turner
> 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.
>
>> 17 teeth?
>>
>> How fast can you push your finger?
>>
>> "-MIKE-"<mi...@mikedrumsDOT.com> wrote in message
>>
>> That may be true, but they still don't do any harm.
>>
>>> 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.
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.
--
See Nad. See Nad go. Go Nad!
-MIKE-
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.
Josepi
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.
"-MIKE-" <mi...@mikedrumsDOT.com> wrote in message
news:i922f7$253$1...@news.eternal-september.org...
-MIKE-
> This was exactly my point.
>
> The other thing, and unfair to the 17 teeth is OK defence is that the
> SawStop pulls the blade away and down. It appears to be grabbed on the back
> side of the blade and the inertia pulls the balde back and under the table
> effectively removing the blade from the finger area. I doubt you would want
> to do this everytime in a **NON**emergency stop. My guess is arbor bending
> would set in after a few dozen of them.
>
> Watch the videos (most have). This is no gentle stop for an armature and saw
> blade of that intertia.
>
> So the retort to the 17 teeth big damage people is still "How fast do you
> push your finger?"
>
> OTOH: Pushing the stock, slipping off, and back handing a running blade can
> be different speeds.
>
I guess I don't know what we're debating, anymore.
I thought we were talking about slowing down the coast of a saw blade
after turning off the power. I guess we got on a tangent.
If it's you're mission to dream up ways to refute the effectiveness of
the SawStop technology... well, I'm off the boat, because you've lost
your mind. :-)
Josepi
some twist about emerg. stopping the blade. Then I jumped in to point out a
difference in technique would be needed and got some resistance. Now I am
chatting with you and who knows whwre it went.
I am not disputing the effectiveness of the SawStop, at all. After seeing
videos I feel I owe the guy something without buying one. Amazing design.
Now I want to kno how to beat it with my wallet.
BTW: never owned a table saw and have never intended to. I know too many
that have lost an eye, fingers, thumb pieces and a **dog to one. When I wave
to somebody I don't want them to think I am giving them the one finger
salute.
**(j/k about the dog...LOL)
"-MIKE-" <mi...@mikedrumsDOT.com> wrote in message
news:i926sd$jkh$1...@news.eternal-september.org...
cl...@snyder.on.ca
wrote:
>
>17 teeth?
>
>How fast can you push your finger?
>
>
>
>"-MIKE-" <mi...@mikedrumsDOT.com> wrote in message
>news:i8vkeg$te2$1...@news.eternal-september.org...
>That may be true, but they still don't do any harm.
>
>
>
>> 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.
>>
Actually significantly LESS than 17 teeth, because the blade is very
quickly slowing down throughout that 1/200 of a second. I believe the
number is something like SEVEN teeth pass the gullet from the time of
contact to full stop, and the last 3 or 4 are pretty well stopped as
they go by.
A demonstation showed a damp peice of cardboard stop the saw with
barely a nick in it.
cl...@snyder.on.ca
No way a caliper could stop the blade in even 4X the time the
saw-stop does. And keeping dust out of the gap between tha "pad" and
the blade would be quite problematic - with dust decreasing the
stopping efficiency by a very large margin.
Dan Coby
Another important part of the SawStop design is that the blade is dropped
below the table's surface as the blade is being stopped.
Hoosierpopi
"electromagnet/solenoid would do the trick"
My God man, you've invented the Saw Stop!
Hoosierpopi
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.
-MIKE-
Hardly.
There's a lot more more going on with that thing than a simple current
running through a magnet.
J. Clarke
cl...@snyder.on.ca says...
I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.
Steve Turner
> On Oct 12, 12:21 pm, Steve Turner<bbqbo...@swtacobell.net.invalid>
> 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?
I've read that about five times and have tried to visualize what you're talking
about, but I'm still puzzled.
> 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.
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?
Bill
> In article<th0ab6t0oquokl2ir...@4ax.com>,
When it snapped (seriously)? I'm not an engineer, so I don't know for
sure. I just wouldn't be surprised. Maybe someone else can opine.
Bill
Bill
> In article<i939j...@news5.newsguy.com>, Bi...@NOSPAM.net says...
> to stop a 3 pound saw blade?
"Pyrotechnics" rather than a master cylinder with brake fluid?
Bill
Josepi
Now we have to define "close"...LOL
"Steve Turner" <bbqb...@swtacobell.net.invalid> wrote in message
news:i935s3$1il$1...@news.eternal-september.org...
J. Clarke
says...
>
> I doubt most people use a pusher stick to cut plywood sheets.
>
> Now we have to define "close"...LOL
General rule is don't have your hands in in line with the blade, or
within 4 inches of it in any direction.
Steve Turner
> I doubt most people use a pusher stick to cut plywood sheets.
First of all, he never said what kind of wood he was cutting, but from what he *did* say I
kinda doubt it was a sheet of plywood. Secondly, I said push "jig", not push "stick", and I
meant one of these:
http://www.tablesawpushstick.com/images/Pushstick%20Safety.jpg
Of course, right there in the description they're calling it a push "stick", which I think
is erroneous. When I hear "push stick", I think of one of these pieces of crap:
http://woodzone.com/Merchant2/graphics/00000001/push-stick.jpg
which I would *never* use; they give me the willies. For plywood, it's entirely plausible
to use a "push block"
http://woodzone.com/Merchant2/graphics/00000001/push-block.jpg
Unless it's a really big sheet of plywood, I use these whenever I can on larger panels to
keep them against the fence and my hands away from the blade. I use a GRR-Ripper for almost
everything else that requires close proximity to the blade.
--
Free bad advice available here.
Markem
<jclark...@cox.net> wrote:
>In article <obabb6p8kmmove0ej...@4ax.com>, markem618
>@hotmail.com says...
>>
>> On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"
>> <jclark...@cox.net> wrote:
>>
>> >I suspect that a small pyrotechnic pressurizing one of the calipers off
>> >my '76 Lincoln might surprise you.
>>
>> Yes but the heat will do what to the saw blade?
>
>About the same thing it does to a brake rotor I suspect, polish the
>sides a little bit.
Uneven heating of a metal disc also would cause it to warp. But then
again the "cartridge" in a Sawstop is toast when activated.
The two times I trimmed my finger nails with a tablesaw was it was a
Delta TS220 I had at the time, I was in a hurry impatient a bit tired,
which equalled being stupid.
The Unisaw which I have now seems safer, and that is more than a
reason to be careful.
Mark
-MIKE-
> On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"
> <jclark...@cox.net> wrote:
>
>> my '76 Lincoln might surprise you.
>
>
Nothing.
A lot more heat is generated by cutting than would be generated in the
half second it would take to slow down the blade.
You guys do realize we're not leaving the motor on in this scenario,
right? :-)
-MIKE-
> -MIKE- wrote:
>> On 10/13/10 7:44 AM, Markem wrote:
>>> On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"
>>> <jclark...@cox.net> wrote:
>>>
>>>> I suspect that a small pyrotechnic pressurizing one of the calipers off
>>>> my '76 Lincoln might surprise you.
>>>
>>> Yes but the heat will do what to the saw blade?
>>>
>>> Mark
>>
>> Nothing.
>> A lot more heat is generated by cutting than would be generated in the
>> half second it would take to slow down the blade.
>>
>> You guys do realize we're not leaving the motor on in this scenario,
>> right? :-)
>>
>
> trick/secret!) : ) I didn't count the mass of the rotor either, or it's
> attached parts, in my other post either. I'm curious now though about
> the calculation (foot/lbs of force).
>
> Bill
>
Sometimes all it takes is a couple of scraps of wood to show how
"little" force is needed. Haven't you ever stopped a coasting blade with
a scrap of wood?
I still see people talking about the SawStop and what it takes for an
emergency stop of the blade. I don't know about anyone else, but all I'm
talking about is a convenience stop.
I suspect a blade could be stopped (at shut-off) in less that a second
with something the size of a bicycle brake and a spring.
-MIKE-
> -MIKE- wrote:
>>> In article<i94fh...@news1.newsguy.com>, Bi...@NOSPAM.net says...
>>> application. A pyro will build pressure rapidly.
>>
>> I didn't think we were talking about an emergency stop.
>> AFAIK, we're discussing a convenience stop which, in my opinion, would
>> be satisfactorily done in a couple seconds, not milliseconds.
>>
>
> I thought we were discussing a stop on the same order as SawStop.
> I didn't read every post in the thread.
>
> Bill
>
Someone brought SawStop into the discussion, which took things on a
tangent.
We started out discussing the OP's link to a set of motor reversing
instructions as a way to slow down the blade for convenience. Then I
proposed the use of a bicycle brake... and things went from there.
Bill
> On 10/13/10 9:43 AM, J. Clarke wrote:
>> In article<i94fh...@news1.newsguy.com>, Bi...@NOSPAM.net says...
Bill
read about flying parts.
Bill
Bill
> On 10/13/10 7:44 AM, Markem wrote:
>> On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"
>> <jclark...@cox.net> wrote:
>>
>>> I suspect that a small pyrotechnic pressurizing one of the calipers off
>>> my '76 Lincoln might surprise you.
>>
>> Yes but the heat will do what to the saw blade?
>>
>> Mark
>
> Nothing.
> A lot more heat is generated by cutting than would be generated in the
> half second it would take to slow down the blade.
>
> You guys do realize we're not leaving the motor on in this scenario,
> right? :-)
>
Yep, thought of that. Gotta break the problem into parts (important
J. Clarke
To stop the saw in a fraction of a revolution, you need rapid
Bill
>>>>> I suspect that a small pyrotechnic pressurizing one of the calipers off
>>>>> my '76 Lincoln might surprise you.
>>>>>
>>>> Bill>
>>>> When it snapped (seriously)? I'm not an engineer, so I don't know for
>>>> sure. I just wouldn't be surprised. Maybe someone else can opine.
>>>J. Clarke>
>>> Why would something that can stop a 4000 pound car "snap" when called on
>>> to stop a 3 pound saw blade?
>> Bill>
>> "Pyrotechnics" rather than a master cylinder with brake fluid?
>
>J. Clarke>
> To stop the saw in a fraction of a revolution, you need rapid
> application. A pyro will build pressure rapidly.
That is what I what I might expect to increase the probability of failure.
Given blade radius and density, and rpm, you could probably integrate to
compute the (foot-pounds of) energy that need to be stopped in a small
fraction of a second (I hope that the dust on the blade won't be an
issue). :) I've seen you post in another "forum" so I believe you are
up to the calculation. I do not have engineering background to back me
up, I'm just thinking it through with you and everyone else who is
reading. Evidently, you'll need to generate the equivalent of an equal
and opposite amount of energy. This means, I think, that you only get
the benefit of a "projection" (dot product) and not all of the force you
can apply to the side of the blade. My reasoning could definitely be
off, maybe a physicist or engineer could help out?
Regards,
Bill
Bill
>>> 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?
>>
>> I've read that about five times and have tried to visualize what you're
>> talking
>> about, but I'm still puzzled.
Think about what would happen if you were walking with a cane, and the
tip of the cane slipped on some ice. It's analogous.
Bill
Markem
<jclark...@cox.net> wrote:
>I suspect that a small pyrotechnic pressurizing one of the calipers off
>my '76 Lincoln might surprise you.
Yes but the heat will do what to the saw blade?
Mark
J. Clarke
Why would something that can stop a 4000 pound car "snap" when called on
Steve Turner
> -MIKE- wrote:
>> Someone brought SawStop into the discussion, which took things on a
>> tangent.
>> We started out discussing the OP's link to a set of motor reversing
>> instructions as a way to slow down the blade for convenience. Then I
>> proposed the use of a bicycle brake... and things went from there.
>>
> Properly done, I bicycle brake sounds like a good idea! I'd hate to read about flying parts.
AHEM. I believe *I* was the one who proposed the use of the bicycle brake. That -MIKE-
character is trying to steal my idea. :-)
-MIKE-
> In article<i94fh...@news1.newsguy.com>, Bi...@NOSPAM.net says...
I didn't think we were talking about an emergency stop.
AFAIK, we're discussing a convenience stop which, in my opinion, would
be satisfactorily done in a couple seconds, not milliseconds.
J. Clarke
About the same thing it does to a brake rotor I suspect, polish the
sides a little bit.
-MIKE-
> On 10/13/2010 12:00 PM, Bill wrote:
>> -MIKE- wrote:
>>> Someone brought SawStop into the discussion, which took things on a
>>> tangent.
>>> We started out discussing the OP's link to a set of motor reversing
>>> instructions as a way to slow down the blade for convenience. Then I
>>> proposed the use of a bicycle brake... and things went from there.
>>>
>> Properly done, I bicycle brake sounds like a good idea! I'd hate to
>> read about flying parts.
>
> AHEM. I believe *I* was the one who proposed the use of the bicycle
> brake. That -MIKE- character is trying to steal my idea. :-)
>
Welllll, looks like I own someone a beer.
Yeppers, I said, "...aftermarket saw brake, under the table.... pads or
rollers or whatever, that would squeeze the blade," and then you brought
up the bike brake.
A good inventor is a better thief. :-)
J. Clarke
Uh, J. Clarke didn't write _any_ of that.
J. Clarke
mi...@mikedrumsDOT.com says...
>
> On 10/13/10 12:06 PM, Steve Turner wrote:
> > On 10/13/2010 12:00 PM, Bill wrote:
> >> -MIKE- wrote:
> >>> Someone brought SawStop into the discussion, which took things on a
> >>> tangent.
> >>> We started out discussing the OP's link to a set of motor reversing
> >>> instructions as a way to slow down the blade for convenience. Then I
> >>> proposed the use of a bicycle brake... and things went from there.
> >>>
> >> Properly done, I bicycle brake sounds like a good idea! I'd hate to
> >> read about flying parts.
> >
> > AHEM. I believe *I* was the one who proposed the use of the bicycle
> > brake. That -MIKE- character is trying to steal my idea. :-)
> >
>
> Welllll, looks like I own someone a beer.
> Yeppers, I said, "...aftermarket saw brake, under the table.... pads or
> rollers or whatever, that would squeeze the blade," and then you brought
> up the bike brake.
>
> A good inventor is a better thief. :-)
And Nikolai Yvanovich Lobachevski is his _name_ . . .
J. Clarke
mi...@mikedrumsDOT.com says...
Well, geez, for that a bicycle brake will work fine.
J. Clarke
Disk brakes work by friction. The energy comes off as heat. Apply F to
the brake, k * F is the braking force where k is the coefficient of
friction.
Back of the envelope it looks like the Lincoln brake at Lincoln pressure
can stop it in about 1/3 revolution. Don't know how much higher
pressure that caliper can take--at 2x the pressure might be able to do
it in 1/6 revolution, which puts it in Sawstop territory.
Puckdropper at dot
news:i94hkb$nhu$1...@news.eternal-september.org:
*snip*
> Of course, right there in the description they're calling it a push
> "stick", which I think is erroneous. When I hear "push stick", I
> think of one of these pieces of crap:
>
> http://woodzone.com/Merchant2/graphics/00000001/push-stick.jpg
>
> which I would *never* use; they give me the willies. For plywood,
> it's entirely plausible to use a "push block"
>
*snip*
Trust your feelings, Steve.
I used that style of push stick for years, until I was cutting a small
piece and pressure on only the one point caused the piece to move and
catch on the back of the blade. The resulting kickback hit me in the
dust mask and broke the push stick. I will not use that style again.
Puckdropper
--
Never teach your apprentice everything you know.
cl...@snyder.on.ca
>I suspect that a small pyrotechnic pressurizing one of the calipers off
>my '76 Lincoln might surprise you.
>
But would also be totally impractical on a 10" saw.
cl...@snyder.on.ca
wrote:
Use a DC motor and a DPDT switch with a big resistor across the "stop"
terminals to short the motor when you shut it off. Stop a 10 inch
blade from 3600rpm in less trha a second with a dead short (if the
switch can handle it) or in about 2 seconds with a good "soft" braking
resistor.
J. Clarke
cl...@snyder.on.ca says...
Which is where this thread started.
J. Clarke
cl...@snyder.on.ca says...
Why would it be "impractical on a 10" saw? The brake rotors on that car
are IIRC 11.5 inch diameter and the whole brake assembly fits inside a
15" wheel.
Bill
Bill
Markem
<jclark...@cox.net> wrote:
>> Use a DC motor and a DPDT switch with a big resistor across the "stop"
>> terminals to short the motor when you shut it off. Stop a 10 inch
>> blade from 3600rpm in less trha a second with a dead short (if the
>> switch can handle it) or in about 2 seconds with a good "soft" braking
>> resistor.
>
>Which is where this thread started.
>
A really big solid state relay and a sealed explosion proof switch,
cause you do not want to start a thread about sawdust explosions.
Right?
You know you can use oars to stir stuff.
Mark
Josepi
*** think *** about what could happen and then prevent it.
In safety training they call this a "barrier"
Minimize the chances with a "barrier". If you cannot absolutely prevent it
think
"Do I have to do this at all" and "Is there another way" and "How can I
make is less risk"
Minimize the damage, if should it happen anyway.
"Puckdropper" <puckdropper(at)yahoo(dot)com> wrote in message
news:4cb62240$0$2367$c3e8da3$9dec...@news.astraweb.com...
Josepi
"J. Clarke" <jclark...@cox.net> wrote in message
news:MPG.271fd67d6...@hamster.jcbsbsdomain.local...
And Nikolai Yvanovich Lobachevski is his _name_ . . .
Josepi
<cl...@snyder.on.ca> wrote in message
news:9macb6pvro2h9a8vq...@4ax.com...
Josepi
work like a charm.
Maybe only because of the background of the guys proposing it.
"J. Clarke" <jclark...@cox.net> wrote in message
news:MPG.271ff998d...@hamster.jcbsbsdomain.local...
cl...@snyder.on.ca
This is all assuming a clean blade for the proper high co-efficient
of friction.
Dust od sap build-up on the blade can change that very quickly.
cl...@snyder.on.ca
wrote:
Nope, just an ex-mechanic wire-head.
cl...@snyder.on.ca
<jclark...@cox.net> wrote:
You want to put that monstrosity on a tilting arbour saw, mounted
under the saw table and in the path of the saw-dust and have it work
reliably???
Not going to happen - guaranteed.
Josepi
with.
The mechanics would be a nightmare to me, also. To others the electronics
would be a nightmare.
Contactor and resistor?...way too complicated.
<cl...@snyder.on.ca> wrote in message
news:4lrcb65g4g641tj4u...@4ax.com...
HeyBub
> This is all assuming a clean blade for the proper high co-efficient
> of friction.
> Dust od sap build-up on the blade can change that very quickly.
Consider what a disk brake caliper has to overcome: dirt, water, oil,
pigeons. It still does a pretty good job.
HeyBub
>>
>> Why would it be "impractical on a 10" saw? The brake rotors on that
>> car are IIRC 11.5 inch diameter and the whole brake assembly fits
>> inside a 15" wheel.
>>
> You want to put that monstrosity on a tilting arbour saw, mounted
> under the saw table and in the path of the saw-dust and have it work
> reliably???
> Not going to happen - guaranteed.
You want to put that goober under a car where it has to contend with dirt,
water, oil, ice, salt, road-kill entrails, and have it work reliably???
Common sense says it won't work and can't be made to work. Don't believe
your lyin' eyes.
J. Clarke
cl...@snyder.on.ca says...
It works reliably on a tilting Lincoln wheel in the path of rain, road
dust, and whatever else mother nature can throw at it, so why does a
nice, dry saw cabinet present such problems?
Do yourself a favor, pull a wheel off your car and _look_ at the
mechanism.
J. Clarke
cl...@snyder.on.ca says...
But we don't know which way it changes. Brake pad material isn't all
that high-friction you know.
J. Clarke
>
> The electornic way would be so much gentler and easier to implement. They
> work like a charm.
>
> Maybe only because of the background of the guys proposing it.
If it "works like a charm" then why can't it slow a dado fast enough to
meet EU regulations?
J. Clarke
says...
>
> As I stated posters seem to lean towards the technology they are comfortable
> with.
>
> The mechanics would be a nightmare to me, also. To others the electronics
> would be a nightmare.
>
> Contactor and resistor?...way too complicated.
So tell us how to wire an induction motor to make the "contactor and
resistor" work.
cl...@snyder.on.ca
wrote:
It's BECAUSE I was a mechanic for several decades that I would NOT use
a brake caliper for the application.
cl...@snyder.on.ca
<jclark...@cox.net> wrote:
>In article <0guto.28451$7m7....@newsfe20.iad>, JRM.@easynews.com
>says...
>>
>> As I stated posters seem to lean towards the technology they are comfortable
>> with.
>>
>> The mechanics would be a nightmare to me, also. To others the electronics
>> would be a nightmare.
>>
>> Contactor and resistor?...way too complicated.
>
>So tell us how to wire an induction motor to make the "contactor and
>resistor" work.
On an induction motor the process is a bit different. Instead of a
resistor across the motor to stop it you use "DC Injection" - in other
words throw about 40 volts DC across the winding for about 2 seconds.
cl...@snyder.on.ca
<jclark...@cox.net> wrote:
I've been doing it for over 45 years
I've also rebuilt a few tilting arbour saws - both belt drive, gear
drive, and direct drive..
cl...@snyder.on.ca
wrote:
It's the clearance issues around a tilting arbour more than the dirt
and sawdust. A purpose built caliper could be used on the opposite end
of the motor on a direct drive saw - but a drum would be just as
effective and smaller for the same stopping power. You don't need the
fade resistance of a disk brake for the application, nor the thermal
mass of a Lincoln car caliper.
Steve Turner
> In article<i94ma4$cp4$1...@news.eternal-september.org>,
> mi...@mikedrumsDOT.com says...
>>
>> On 10/13/10 9:43 AM, J. Clarke wrote:
>>> In article<i94fh...@news1.newsguy.com>, Bi...@NOSPAM.net says...
>>>>
>>>> J. Clarke wrote:
>>>>> In article<i939j...@news5.newsguy.com>, Bi...@NOSPAM.net says...
>>>>>>
>>>>>> J. Clarke wrote:
>>>>>>> In article<th0ab6t0oquokl2ir...@4ax.com>,
>>>>>> sure. I just wouldn't be surprised. Maybe someone else can opine.
>>>>>
>>>>
>>>> "Pyrotechnics" rather than a master cylinder with brake fluid?
>>>
>>> application. A pyro will build pressure rapidly.
>>
>> AFAIK, we're discussing a convenience stop which, in my opinion, would
>> be satisfactorily done in a couple seconds, not milliseconds.
>
> Well, geez, for that a bicycle brake will work fine.
Another reality check for all the people taking this thread off into the wild blue yonder is
the issue of getting the blade onto the arbor in the presence of calipers that grip either
side of the blade. My interest (and Mike's as well, I think) in using a bicycle brake was
simply a matter of "how can I retrofit my existing table saw with a simple convenience
brake?" I think the wide-opening jaws of a bicycle brake (maybe along with some kind of
front-side cable disconnect to allow the calipers to drop out of the way) would allow enough
clearance to get the blade on the arbor without too much trouble. This heavy-duty
automotive caliber Saw-Stop alternative that everybody else is talking about would also have
to provide a similar mechanism, which would of course add to the complexity.
--
So will there ever be a day, throughout the rest of my life, that I
won't encounter in the written word a case of somebody not understanding
the difference between the meanings of the words "to" and "too"?
To reply, eat the taco.
http://www.flickr.com/photos/bbqboyee/
J. Clarke
cl...@snyder.on.ca says...
So now you have to add a power supply and controls.