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25-03-2004, 10:42 PM
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#76
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Re: Why would a garage door torsion spring break & is two better than one?
brokenklutz@yahoo.com (DIY Klutz) wrote in message news:<1dfb2e58.0402250518.48670ed0@posting.google.com>...
> Since IPPT is so important, I'm trying to derive it for my springs
> given the torsion spring formulas in the web site below:
> http://www.srl.gatech.edu/education...mer/torsion.htm
I an NOT a garage door torsion spring expert (I too never realized until
this informative thread that there was a torsion spring in my doorway).
I think the equation listed at that web URL is off by a factor of 1/2 pi
The equation I derived from basic physics is (1/2 pi) more than that one:
K = (pi^2 * d^4 * E) / (32 * L)
where d is the diameter of your wire, E is Young's Modulus of Elasticity
for the spring material, and L is the total length of your wire (were
that wire to be uncoiled into a straight line).
If you prefer to format that equation from a straight line to a wire coil,
it should convert to:
K = (pi * d^4 * E) / (32 * N * D)
where N is the number of active coils and D is the true diameter of the
garage door torsion spring from the center of the coil to the center
of the wire. Again, my equation is off from yours by a factor of 1/2 pi.
Note your true diameter D = ID + ((OD - ID)/2)
D = 1.740 + ((2.250 - 1.740)/2
D = 1.740 + (0.510/2)
D = 1.740 + 0.255
D = 2.0 inches
Note your effective circumference C = pi * D
C = 3.14 * 2.0
C = 6.28 inches
Note your effective wire length L = (C * N)
L = 6.28 * 127
L = 798 inches
Plugging in the numbers you provided seems to arrive at an IPPT of:
K = (pi * d^4 * E) / (32 * N * D)
K = (3.14 * 0.256^4 * 3e7) / (32 * 127 * 2.0)
K = 49.78 inch pounds per turn
Ellen
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25-03-2004, 10:42 PM
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#77
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Re: Why would a garage door torsion spring break & is two better than one?
brokenklutz@yahoo.com (DIY Klutz) wrote in message news:<1dfb2e58.0402250518.48670ed0@posting.google.com>...
> To find the spring stiffness (K), I used the formula from that web page:
> K = d^4 E / 64 D N
Upon further inspection, this formula appears to be the spring constant
PER RADIAN (and not per turn).
2 pi radians can fix that.
Ellen
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25-03-2004, 10:42 PM
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#78
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Re: Why would a garage door torsion spring break & is two better than one?
According to Ellen Spelling <spellinellen@yahoo.com>:
> doordoc@prodigy.net (Doordoc) wrote in message
> news:<63b5749d.0402242104.74e10bcf@posting.google.com>...
> We do some commercial doors that
> > have 100,000 cycles, but that would be overkill on most residential
> > doors since the springs would outlast the rest of the door.
> That brings up the question of why only a mere 10,000 cycles?
> So many garage door springs seem to be breaking (virtually everyone
> in this thread has reported a broken torsion spring),
That's like ER nurse saying everybody must be sick, because all they
see is sick people ;-)
Remember that there's probably 100's of thousands of people subscribed
to the groups that this article is appearing in...
> What am I missing?
Probably a simple matter of most people don't use their doors anywhere
near like you do (we probably average 5 cycles/month). And secondly, in
the past, there may have been a big differential between 10,000 cycle and
20,000 cycle springs. The engineering involved is a lot more sophisticated
than it was 20 years ago, so there's more choice, better specifications,
and better specification control.
But you know what to buy when your current springs break...
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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25-03-2004, 10:43 PM
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#79
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Re: Why would a garage door torsion spring break & is two better than one?
> Plugging in the numbers you provided seems to arrive at an IPPT of:
> K = (pi * d^4 * E) / (32 * N * D)
> K = (3.14 * 0.256^4 * 3e7) / (32 * 127 * 2.0)
> K = 49.78 inch pounds per turn
>
> Ellen
I don't know anything about the formulas both of you are using but
obviously your formula is accurate since the IPPT of his spring (250 x
1-3/4 x 33) is 45.23 according to the spring calculator software you
referred to if you use the full length of the spring and 49.95 if you
use 30" for the active length.
We simply take the weight of the door multiplied by the multiplier for
the drum (approx .39 to .40) to determine the IPPT that is required.
Sorry but most garage door people aren't into figuring out how the
IPPT of the spring is determined.
Doordoc
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25-03-2004, 10:43 PM
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#80
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Re: Why would a garage door torsion spring break & is two better than one?
> Who chose 10,000 anyway? Nobody asked me.
It has been an industry standard for pretty much since they started
making torsion springs (don't remember the year but was somewhere
around the 1940's or 50's in Toledo, OH) & the springs will normally
last most owners 7-8 years during normal use.
> Since the total repair cost is three (or more) times that, wouldn't we
> save ooodles of money simply by doubling the life of the spring?
>
As much as you use your door, yes you would save oodles of money
>
> My point is, the 19,000 duty cycle torsion spring is about the same
> cost as the 10,000 duty cycle spring. And that 10,000 seems vastly
> too low. So, why not go with the 19,000 (or even greater) every time?
>
> What am I missing?
>
> Ellen
A big difference on the material cost whether one is a dealer or a
manufacturer when buying springs in bulk or by the truck load is the
weight. Steel & freight is paid for by the pound, so in bulk
quantities the difference is very substantial. However, when they are
bought one or two at a time there would be very little difference in
cost.
The amount of weight a garage door service vehicle can carry is also
limited and the more weight they carry the more wear & tear there is
on the vehicles and the truck will break down more often & will be
more expensive to repair.
As with most things, everything can't be fair for everybody, so most
things will be very close to the middle ground.
Doordoc
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25-03-2004, 10:44 PM
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#81
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Re: Why would a garage door torsion spring break & is two better than one?
doordoc@prodigy.net (Doordoc) wrote in message news:<63b5749d.0402261704.19edac7e@posting.google.com>...
> > Who chose 10,000 anyway? Nobody asked me.
>
> It has been an industry standard for pretty much since they started
> making torsion springs (don't remember the year but was somewhere
> around the 1940's or 50's in Toledo, OH) & the springs will normally
> last most owners 7-8 years during normal use.
>
> The amount of weight a garage door service vehicle can carry is also
> limited and the more weight they carry the more wear & tear there is
> on the vehicles and the truck will break down more often & will be
> more expensive to repair.
Chris Lewis' ER comment is apropos in that most of us were oblivious
to
the garage door torsion spring until that fateful day (crack) ...
I'd agree with Duane that Doordoc has been right on the money in
all his posts I've seen (I lurked in the archives before posting).
The weight of the 19,000 cycle spring that Ellen calculated in this
thread (15.34 pounds) is indeed fifty percent greater than the weight
of the 10,000 cycle garage door torsion spring (a mere 11.52 pounds).
I can see that this weight on the torsion bar, once installed, would
make
no difference whatsoever to the homeowner; but, as Doordoc noted, the
repairman's truckload would increase by 50% with no likely change in
profit.
More likely, the repairman's carry-on inventory would, of necessity,
go DOWN (with the result, again, of no likely increase in profit).
Worse yet, fewer correct springs might be replaced on the first call
as a
result of less varied inventory (how many times does the repairman
actually
call ahead to determine the exact spring size?).
More to the point:
Q: Has anyone in this thread been given a choice of springs by the
repairman?
(based on the duty cycle)
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25-03-2004, 10:44 PM
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#82
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Re: Why would a garage door torsion spring break & is two better than one?
brokenklutz@yahoo.com (DIY Klutz) wrote:
>...Q: Has anyone in this thread been given a choice of springs by the
>repairman?
> (based on the duty cycle)
>
While I don't remember the exact cycle numbers, I was given the option of
replacing my springs with either "identical" or "upgraded" springs last time
they broke. The cost difference was pretty minimal, ten or fifteen bucks.
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25-03-2004, 10:45 PM
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#83
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Re: Why would a garage door torsion spring break & is two better than one?
doordoc@prodigy.net (Doordoc) wrote in message news:<63b5749d.0402211752.68319686@posting.google.com>...
> Actually the number of the springs has nothing to do with how long
> they last. It is all a matter of the wire size, the length of the
> spring, & the inside diameter of the spring.
Sorry but I'm *still* a bit confused about this onesey twosey thing.
If it doesn't really matter how many garage door torsion springs
are installed; and if all that matters is the dimension of the
torsion springs (based on the door load) - then why would anyone
go to the (double) trouble of installing TWO garage door torsion
springs when they could just as well do with ONE?
For example, why would I keep two spare tires in my trunk?
Why would I have the mason put in two chimneys for my fireplace?
Why would I install two sprinkler systems for my lawn?
It seems just as unreasonable to me to have two springs?
(based on the information in this helpful thread)
Can someone set me straight on this quest?
Ellen
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25-03-2004, 10:47 PM
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#84
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Re: Why would a garage door torsion spring break & is two better than one?
"Ross" <vze4kz2u@verizon.net> wrote in message news:<ETNXb.14277$5W3.5326@nwrddc02.gnilink.net>...
> Adjusting garage door torsion type balance springs is best left to the
> experienced professional. The danger presented as you tension the spring
> should not be taken lightly. I know one individual who suffered a severe
> hand injury when the spring "got away," similar to a window shade spring,
> but fully exposed and with far more force!
From: Doorman (lunger@istream.com)
Subject: Re: Garage Door Ratings/Opinions
Newsgroups: alt.home.repair
Date: 1999/10/24
....
Counterbalance assembly. The industry standard is 10,000 cycles. I
personally think the type you wind up with a drill is well, for lack of a
better term Mickey mouse. Some are better than others and I sure hate to see
plastic used for torsion spring components. Here's the acid test. Phone up
a dealer that handles that type of door and tell him your spring is broken.
Ask them what it would cost to replace it. They are safer, but all this
taboo about garage door counterbalances being extremely dangerous has a lot
to do with litigation rather than safety. It is true that a few people have
been injured when fooling around with these things, but people have been
injured doing all kinds of things. Do you ever hear that you shouldn't buy a
table saw because you can cut your fingers off. Utter nonsense.
The torsion counterbalance assembly should have good quality bearings
throughout and preferably ones that you can oil. The rollers that run in the
track can be either nylon or steel as both stand up very well providing they
are well built and you can usually tell by looking at them. If they have
bearings, ask the dealer if they are sealed (not that important) or case
hardened (very important.) Some of the nylon ones that are available
actually stand up quite well without bearings. They simply roll on the
roller shaft like the wheel on a kids wagon.
.... (complete message in the archives) ...
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25-03-2004, 10:48 PM
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#85
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Re: Why would a garage door torsion spring break & is two better than one?
In article <d2d93df1.0403010513.1a48f643@posting.google.com>, Like I said before wrote:
> to do with litigation rather than safety. It is true that a few people have
> been injured when fooling around with these things, but people have been
> injured doing all kinds of things. Do you ever hear that you shouldn't buy a
> table saw because you can cut your fingers off. Utter nonsense.
Delta has to make a special shorter spindle for the blades on Unisaws if
they are to be sold in EU countries. This is to prevent the use of dado
blades on saws sold in Europe. (FYI - a dado blade is used to make a wide
cut - up to an inch or more. Some are "wobble" - a tilted blade on the
spindle to get the wide cut, and some are stacked blades.) The reasoning is
that dado blades are too dangerous for consumers to use.
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