In the thread on SawStop, the issue of making saws stop rotating shortly
after the user turned the power off came up, with the central example
being miter saws, which stop in a few seconds after the trigger is
released.

But it was not clear how this worked, and if it was more widely
applicable.

Anyway, I did a little research, and found the governing patent. The
electric brake was invented by Black and Decker, and apparently licensed
widely.

The patent is 6,037,729. To get a copy, go to http://www.pat2pdf.org
and follow the directions.

This approach is intended for universal motors, as used on small saws
and drills and routers, and is not directly applicable to induction
motors, as used in table saws.

Joe Gwinn

"Joseph Gwinn" wrote in message
...
In the thread on SawStop, the issue of making saws stop rotating shortly
after the user turned the power off came up, with the central example
being miter saws, which stop in a few seconds after the trigger is
released.

But it was not clear how this worked, and if it was more widely
applicable.

Anyway, I did a little research, and found the governing patent. The
electric brake was invented by Black and Decker, and apparently licensed
widely.

The patent is 6,037,729. To get a copy, go to http://www.pat2pdf.org
and follow the directions.

This approach is intended for universal motors, as used on small saws
and drills and routers, and is not directly applicable to induction
motors, as used in table saws.

Yeah, but to get SawStop-type decelerations, you'd proly need motor windings
as thick as yer pinky.
iiuc, electric braking is wear'n'tear on the motor windings.

The discussion continued under the thread Ping Leon: Design Q on sawstop,
in rec.woodworking, which turned into a bunch of silly backbiting with those
silly territorial rw ninnies, but still some inneresting points, alternative
strategies were discussed -- namely, that you don't really need to STOP the
blade so suddenly, as much as just *get it out of the way in a hurry*, which
can be done in a mouse-trap trigger like setup with standard springs, with
large but realistic forces. Then a non-destructive rapid deceleration is
possible, with regular ole piston disk-brake calipers.
Some calcs appear in that thread.

There are still other solutions, one of the biggest being education, imo.
Out of sight/out of mind "solutions" like Sawstop create out of sight/out of
mind mentalities, where people now expect *everything* to cater to their
well-being.

All lost on the rec.woodworking peeple, but wtf, they seem obsessed with
dildos anyway.... I mean, dado's....

I think all this smacks of the crawling helmet.
http://www.dailymail.co.uk/femail/ar...g-helmets.html

Imo, Stephen (G)ass of sawstop is tryna mind**** Congress (to LEGISLATE the
sawstop into yer shop), just like these crawling helmet assholes are
mind****ing idiot parents. Same ****, different product.
--
EA


Joe Gwinn

In article ,
"Existential Angst" wrote:

"Joseph Gwinn" wrote in message
...
In the thread on SawStop, the issue of making saws stop rotating shortly
after the user turned the power off came up, with the central example
being miter saws, which stop in a few seconds after the trigger is
released.

But it was not clear how this worked, and if it was more widely
applicable.

Anyway, I did a little research, and found the governing patent. The
electric brake was invented by Black and Decker, and apparently licensed
widely.

The patent is 6,037,729. To get a copy, go to http://www.pat2pdf.org
and follow the directions.

This approach is intended for universal motors, as used on small saws
and drills and routers, and is not directly applicable to induction
motors, as used in table saws.

Yeah, but to get SawStop-type decelerations, you'd proly need motor windings
as thick as yer pinky.
iiuc, electric braking is wear'n'tear on the motor windings.

The brake winding is no heavier than the run winding, according to the
patent.

The guarantee is to stop the blade in no more than six seconds, which
implies that the typical time is about three seconds.

The mechanism described in the patent requires that the brushes and
commutator be in good condition, as well as the switches.

As for induction motors, rapid stop is implemented in almost all VFDs,
by a related but different mechanism.


The discussion continued under the thread Ping Leon: Design Q on sawstop,
in rec.woodworking, which turned into a bunch of silly backbiting with those
silly territorial rw ninnies, but still some inneresting points, alternative
strategies were discussed -- namely, that you don't really need to STOP the
blade so suddenly, as much as just *get it out of the way in a hurry*, which
can be done in a mouse-trap trigger like setup with standard springs, with
large but realistic forces. Then a non-destructive rapid deceleration is
possible, with regular ole piston disk-brake calipers.
Some calcs appear in that thread.

The subject of the present thread is how miter saw electric brakes work,
and more generally how to stop induction motors, and is not a
continuation of the SawStop thread, which has degenerated, as you
mention.

Joe Gwinn

"Joseph Gwinn" wrote in message
...
In article ,
"Existential Angst" wrote:

"Joseph Gwinn" wrote in message
...
In the thread on SawStop, the issue of making saws stop rotating
shortly
after the user turned the power off came up, with the central example
being miter saws, which stop in a few seconds after the trigger is
released.

But it was not clear how this worked, and if it was more widely
applicable.

Anyway, I did a little research, and found the governing patent. The
electric brake was invented by Black and Decker, and apparently
licensed
widely.

The patent is 6,037,729. To get a copy, go to http://www.pat2pdf.org
and follow the directions.

This approach is intended for universal motors, as used on small saws
and drills and routers, and is not directly applicable to induction
motors, as used in table saws.

Yeah, but to get SawStop-type decelerations, you'd proly need motor
windings
as thick as yer pinky.
iiuc, electric braking is wear'n'tear on the motor windings.

The brake winding is no heavier than the run winding, according to the
patent.

The guarantee is to stop the blade in no more than six seconds, which
implies that the typical time is about three seconds.

The mechanism described in the patent requires that the brushes and
commutator be in good condition, as well as the switches.

As for induction motors, rapid stop is implemented in almost all VFDs,
by a related but different mechanism.


The discussion continued under the thread Ping Leon: Design Q on
sawstop,
in rec.woodworking, which turned into a bunch of silly backbiting with
those
silly territorial rw ninnies, but still some inneresting points,
alternative
strategies were discussed -- namely, that you don't really need to STOP
the
blade so suddenly, as much as just *get it out of the way in a hurry*,
which
can be done in a mouse-trap trigger like setup with standard springs,
with
large but realistic forces. Then a non-destructive rapid deceleration is
possible, with regular ole piston disk-brake calipers.
Some calcs appear in that thread.

The subject of the present thread is how miter saw electric brakes work,
and more generally how to stop induction motors, and is not a
continuation of the SawStop thread, which has degenerated, as you
mention.

I was just highlighting the point that there is rapid stop, and there are
..001 sec stops.

And also that even 6 sec braking can be tough on motor windings, if what I
read was correck.
Would be nice, in electric brake systems, to be able to switch it off when
it isn't nec, and it is not always nec -- like the manual brake on lathes.
Unless yer switching parts in a snap-handle collet, no point in wearing out
the brake if coasting to a stop is ok.

Also, there are at least three types of electric brakes: two types of
regenerative: the stuff you are talking about is proly an "internal" type,
thru winding switching. There is also regenerative braking back into the
"grid", or thru high-power resistors.
Or, you just power the motor backwards! Which would require pinky-sized
wiring....
--
EA



Joe Gwinn

On Thursday, December 13, 2012 10:53:55 AM UTC-6, Existential Angst wrote:
"Joseph Gwinn" wrote in message

...

In article ,

"Existential Angst" wrote:



"Joseph Gwinn" wrote in message

...

In the thread on SawStop, the issue of making saws stop rotating

shortly

after the user turned the power off came up, with the central example

being miter saws, which stop in a few seconds after the trigger is

released.



But it was not clear how this worked, and if it was more widely

applicable.



Anyway, I did a little research, and found the governing patent. The

electric brake was invented by Black and Decker, and apparently

licensed

widely.



The patent is 6,037,729. To get a copy, go to http://www.pat2pdf.org

and follow the directions.



This approach is intended for universal motors, as used on small saws

and drills and routers, and is not directly applicable to induction

motors, as used in table saws.



Yeah, but to get SawStop-type decelerations, you'd proly need motor

windings

as thick as yer pinky.

iiuc, electric braking is wear'n'tear on the motor windings.



The brake winding is no heavier than the run winding, according to the

patent.



The guarantee is to stop the blade in no more than six seconds, which

implies that the typical time is about three seconds.



The mechanism described in the patent requires that the brushes and

commutator be in good condition, as well as the switches.



As for induction motors, rapid stop is implemented in almost all VFDs,

by a related but different mechanism.





The discussion continued under the thread Ping Leon: Design Q on

sawstop,

in rec.woodworking, which turned into a bunch of silly backbiting with

those

silly territorial rw ninnies, but still some inneresting points,

alternative

strategies were discussed -- namely, that you don't really need to STOP

the

blade so suddenly, as much as just *get it out of the way in a hurry*,

which

can be done in a mouse-trap trigger like setup with standard springs,

with

large but realistic forces. Then a non-destructive rapid deceleration is

possible, with regular ole piston disk-brake calipers.

Some calcs appear in that thread.



The subject of the present thread is how miter saw electric brakes work,

and more generally how to stop induction motors, and is not a

continuation of the SawStop thread, which has degenerated, as you

mention.



I was just highlighting the point that there is rapid stop, and there are

.001 sec stops.



And also that even 6 sec braking can be tough on motor windings, if what I

read was correck.

Would be nice, in electric brake systems, to be able to switch it off when

it isn't nec, and it is not always nec -- like the manual brake on lathes.

Unless yer switching parts in a snap-handle collet, no point in wearing out

the brake if coasting to a stop is ok.



Also, there are at least three types of electric brakes: two types of

regenerative: the stuff you are talking about is proly an "internal" type,

thru winding switching. There is also regenerative braking back into the

"grid", or thru high-power resistors.

Or, you just power the motor backwards! Which would require pinky-sized

wiring....

--

EA







Joe Gwinn

Don't forget DC injection for stopping motors..
It is not regenerative, and it is not running it backwards..

In article ,
Cross-Slide wrote:

On Thursday, December 13, 2012 10:53:55 AM UTC-6, Existential Angst wrote:
"Joseph Gwinn" wrote in message

[snip]

Also, there are at least three types of electric brakes: two types of

regenerative: the stuff you are talking about is proly an "internal"
type,

thru winding switching. There is also regenerative braking back into the

"grid", or thru high-power resistors.

Or, you just power the motor backwards! Which would require pinky-sized

wiring....

--

EA







Joe Gwinn

Don't forget DC injection for stopping motors..
It is not regenerative, and it is not running it backwards..

Yes, that's been mentioned before. I think that's how VFDs stop the
motor as well.

Joe Gwinn


PS: By the way, there is something wrong with how quoting works in your
newsreader - everything ends up double-spaced. Perhaps a configuration
problem? JMG

In article ,
"Existential Angst" wrote:

"Joseph Gwinn" wrote in message
...
In article ,
"Existential Angst" wrote:

"Joseph Gwinn" wrote in message
...
In the thread on SawStop, the issue of making saws stop rotating
shortly
after the user turned the power off came up, with the central example
being miter saws, which stop in a few seconds after the trigger is
released.

But it was not clear how this worked, and if it was more widely
applicable.

Anyway, I did a little research, and found the governing patent. The
electric brake was invented by Black and Decker, and apparently
licensed
widely.

The patent is 6,037,729. To get a copy, go to http://www.pat2pdf.org
and follow the directions.

This approach is intended for universal motors, as used on small saws
and drills and routers, and is not directly applicable to induction
motors, as used in table saws.

Yeah, but to get SawStop-type decelerations, you'd proly need motor
windings
as thick as yer pinky.
iiuc, electric braking is wear'n'tear on the motor windings.

The brake winding is no heavier than the run winding, according to the
patent.

The guarantee is to stop the blade in no more than six seconds, which
implies that the typical time is about three seconds.

The mechanism described in the patent requires that the brushes and
commutator be in good condition, as well as the switches.

As for induction motors, rapid stop is implemented in almost all VFDs,
by a related but different mechanism.


The discussion continued under the thread Ping Leon: Design Q on
sawstop,
in rec.woodworking, which turned into a bunch of silly backbiting with
those
silly territorial rw ninnies, but still some inneresting points,
alternative
strategies were discussed -- namely, that you don't really need to STOP
the
blade so suddenly, as much as just *get it out of the way in a hurry*,
which
can be done in a mouse-trap trigger like setup with standard springs,
with
large but realistic forces. Then a non-destructive rapid deceleration is
possible, with regular ole piston disk-brake calipers.
Some calcs appear in that thread.

The subject of the present thread is how miter saw electric brakes work,
and more generally how to stop induction motors, and is not a
continuation of the SawStop thread, which has degenerated, as you
mention.

I was just highlighting the point that there is rapid stop, and there are
0.001 sec stops.

And also that even 6 sec braking can be tough on motor windings, if what I
read was correck.

Six seconds isn't that hard on a small motor. And lots of big lathes
powered by three-phase motors do plug reversing, where two wires are
abruptly reversed, causing the motor to be driven backwards. Industrial
motors are designed to tolerate this. And I assume that miter saw
makers like B&D also design their motors to tolerate electric braking.

I have the VFD driving my lathe (Clausing 5914) configured to stop
rotation in one second.


Would be nice, in electric brake systems, to be able to switch it off when
it isn't nec, and it is not always nec -- like the manual brake on lathes.
Unless yer switching parts in a snap-handle collet, no point in wearing out
the brake if coasting to a stop is ok.

This can be done in B&D's design. I've read that there are three wires
between the motor assembly and the switch assembly, red, black, and
gray, and that if one interrupts the gray wire, the electric brake is
disabled.


Also, there are at least three types of electric brakes: two types of
regenerative: the stuff you are talking about is proly an "internal" type,
thru winding switching. There is also regenerative braking back into the
"grid", or thru high-power resistors.


Or, you just power the motor backwards! Which would require pinky-sized
wiring....

See plug reversing, above. And, no, the windings aren't any larger than
normal.

And, the B&D approach actually does drive in reverse for a moment. This
is explained in the patent.

Joe Gwinn

On Thu, 13 Dec 2012 21:33:57 -0500, Joseph Gwinn
wrote:


Or, you just power the motor backwards! Which would require pinky-sized
wiring....

See plug reversing, above. And, no, the windings aren't any larger than
normal.

And, the B&D approach actually does drive in reverse for a moment. This
is explained in the patent.

Joe Gwinn
Some of the early "fast stop" saws just used a 2 position switch. One
position put both lines to the motor terminals. The other position
shorted the motor terminals while disconnected from the line.
Basically just shorted the "generator" output.

Again, just works on universal, or brush style motors -( and works
better on permanent magnet (DC) motors which are usually used on
battery powered motors) It does not bring the motor to a rapid and
sure stop, but it really reduces the spin-down time significantly.