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On Dec 8, 10:55 am, "Existential Angst" wrote:
wrote in message
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On Dec 8, 8:36 am, "Existential Angst" wrote:
There seems to be two mechanical strategies at work in the SawStop, of
translation, and of rotation, ie, retracting the blade, and stopping the
rotation.
It seems to me one would be sufficient, with retraction having the
advantage
of being non-destructive. Not sure if the blade is direct drive or belt
drive, but if it was belt drive, the retraction could all the more
rapid,
since you would not have to retract the mass of a relatively heavy
motor.
In fact, if designed properly, you could proly have only the blade and
its
bearing retract, along grooved guides of some sort, allowing for a very
rapid acceleration from whatever force is applied -- presumably springs?
But could also be pneumatic or hydraulic, or solenoidal.
Unless the deceleration of rotation is just an inherently faster process
than the retraction process.
But, from what I see, it seems the retraction is occurring FIRST,
anyway,
to
initiate the destructive crash, so mebbe the rotational issue is
irrelevant??
In the videos I've seen the blade is fully stopped, while
the retraction is only partial, more like the retraction
has only started.
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http://www.youtube.com/watch?v=eiYoB...endscreen&NR=1
1:45 the retraction looks pretty complete to me.
BUT, at 2:50, which shows the whole process, it appears that the
retraction
occurs AFTER the collision thingy engages.
Yet, at 1:45, the retraction seem instantaneous, upon touching the hot
dog.... Go figger.
Well, one is normal speed video, the other is high-speed
photography that is slowed down so you can actually
see what is happening.
At the 1:45 normal speed spot all you see is the top of the saw
and it's impossible to determine any sequence of
events. At the 2:50 area it's clear that a substantial amount
of the movement is ocurring after the saw blade has
stopped spinning.
Also, what "tired" just posted makes sense. The saw
has momentum that has to go somewhere. One place
to dissipate it is to allow the blade to go down in a
controlled fashion. It could be that is all they use. If so,
the sequence would be that the pawl engages first
and as it stops the saw, the momentum then causes
the retraction.
And I think one problem with relying only
on retraction would be that it's not going to be fast
enough to get all or enough of the blade out of the way.
You could do the math and find the force necessary
to move a given mass several inches in 1ms.
=================================================
10,000 newtons per cm of retraction for a 1 kg (2.2#) mass, or about 4x
the
weight of a 200# guy.
If 1/2 cm was suff, and the unit to be accelerated was only 1/2 kg, then
it
would only be 200# of force, a lot more manageable.
800# is actually not a cosmically large force, given that some people can
lift 800#, but it's perhaps a bit to apply in a very small area. And mebbe
too expensive to implement.
I would expect the mass is more than 2.2 lbs.
And not clear how you'd apply such a large force.
If you used a spring for example, the mass of the spring
also has to be accounted for because you're also
accelerating that.
=============================================
Depends how you design it. I could see a strong magnesium housing to a
belt-driven blade being pretty lite.
And actually, a large spring IS the force-provider. Basically you'd have a
mouse-trap type situation, where a very small/fast actuator trips the
spring, which then applies the accelerating force -- one on each side of the
blade could supply wicked fast accelerations.
For example, Lee Spring in NYC has dies springs with spring constants of
over 2,000 # per inch.... and that's just one spring. So these forces are
easily obtainable in very small spaces, more than adequate for even multi-kg
blade housings.
Heh, resetting the blade, tho, would require crowbar.... LOL
But actually, could be done with fine-thread "resetting screw", might take a
cupla minutes.
A side question is why have the retraction at all.
I guess if you're flopping a whole arm down on the
saw, it would prevent injury from just hitting a stopped
blade.
==================================================
I suspect the retraction is not for retraction's sake but as a kind of
force
reaction to the stopped blade, preventing more damage than is already
occurring.
From "tired"'s reply it is indeed the saw momentum.
But he seems to imply that it also prevents the injury by
pulling the blade away. We'd have to see a very high-speed
close up of the hot dog video to see the exact sequence
and if the saw stopping alone isn't sufficient.
Now, if rotation is still an issue, wouldn't a caliper/rotor brake type
deal
be as fast as his collision process, AND be non-destructive? Mebbe
multiple
calipers.
It would have to be one hell of a caliper brake to stop that
spinning saw in 1ms. With the way it's implemented now,
at first contact of the jamb the saw is stopped dead.
================================================== ===
Here's a way to do it:
If a quick retraction occurs over a relatively small distance, AND a
caliper-applied deceleration then occured (non-destructive), you'd have a
more time to stop the blade rotation, ie less demanding braking, no
trashed
blade.
Yes, IF you could retract it quicker than a finger can advance
for as long as it takes to stop the saw.
To wit:
Suppose the retraction was about 1/2" (roughly 1 cm). Wood is fed into a
saw somewhere around .25-1 ft/sec, wo we'll use 12"/sec.
Now, upon the 1/2" retraction, the hand won't contact the blade for
another
50 milliseconds, giving the blade 50x longer to stop, before the hand has
another chance to contact the blade -- a whole lot easier to accomplish
than a 1 millisecond stop.
I suspect the most feasible way to accomplish this kind of retraction is
with bigazz spring (proly two, on either side of the blade, moving two
bearings), triggered much the way the spring of his jamb-ditty is applied,
with the calipers simultaneously engaging.
Heh, and these calipers can act as a brake on the saw during normal use,
as
well, instead of electric motor braking. Lathes often have a frictional
stop system, using a drum-like squeeze brake, very handy.
Oh, oh, but then he wouldn't be able to sell new crumple ditties at
$70/pop.....
Mebbe you could run this by (G)ass, ask him to send me $5 if he likes
the
idears.
You really think he didn't think of a simple brake,
like they have on say lawn mowers, first?
================================================
Mebbe he dudn't drive, or mow his lawn.
Or mebbe just invite me to one of them 'spensive luncheons, where
he's twisting CONgress's arms on safety'n'****, you know, for all the
li'l
children....
--
EA
Or better yet that anyone involved in this is interested in
answering your questions, given all the insults and names
you've called them?
===============================================
Like they don't warrant it, right?
These corrupt assholes couldn't give a goddamm about you'n'me, but they
are
surefire quick to up the regulational ante, and then **** the public for
the
slightest transgression. Municipal penalty pricing, donchaknow.
With high enough penalties, they could eliminate taxes, and still remain
in
the black.
--
EA- Hide quoted text -
- Show quoted text -
I've only looked into the SS itself a bit. I haven't looked into
what the inventor is or isn't doing regarding politicians, making
it mandatory, etc.
==================================================
Well, a few replies in the previous thread addressed this, and some forums
have discussed this at length. The almost universal consensus so far is
that his tactics/lobbying, altho legal, are manipulative and greed-driven.
(G)ass is quite at home with the lobbyists..
All's you gotta do is scream Safety loud enough, or " ....the li'l
children...". and BAM, everyfuknthing stops, sense goes out the window, and
you can rip off the system to yer heart's content. Ergo, Crawling Helmets.
I think that whiney asshole TiredofSpam has color-coordinated crawling
helmets, to match his diapers and Superman cape.
--
EA