I need help in selecting an extension spring to counterbalance most of a
3.5# load over a hair less than 1" of travel. The 3.5# load needs to
rest solidly against the bottom stop at rest, and I need most of the
3.5# load counterbalanced through the 1" stroke, so it seems I need a
spring where the rate will not change significantly over that 1" travel.
I have a good amount of room to mount a fairly long spring, up to about
5" contracted length.

I see plenty of springs on McMaster to choose from, but I'd like to be
able to order the correct spring the first time.

Thanks!

Pete C. wrote:
I need help in selecting an extension spring to counterbalance most of a
3.5# load over a hair less than 1" of travel. The 3.5# load needs to
rest solidly against the bottom stop at rest, and I need most of the
3.5# load counterbalanced through the 1" stroke, so it seems I need a
spring where the rate will not change significantly over that 1" travel.
I have a good amount of room to mount a fairly long spring, up to about
5" contracted length.

I see plenty of springs on McMaster to choose from, but I'd like to be
able to order the correct spring the first time.

Thanks!

Before you order, you would be better asking the question from a aspring
maker.
He will know the modulous of elasticity of different thicknesses of
steel wire at what diameter coil.
IE spring rate in ozor lbs per 1" of movement.
then when you have this information you can order up a spring to do
the task you specify.

On Mon, 14 Dec 2009 13:41:54 -0600, "Pete C."
wrote:


I need help in selecting an extension spring to counterbalance most of a
3.5# load over a hair less than 1" of travel. The 3.5# load needs to
rest solidly against the bottom stop at rest, and I need most of the
3.5# load counterbalanced through the 1" stroke, so it seems I need a
spring where the rate will not change significantly over that 1" travel.
I have a good amount of room to mount a fairly long spring, up to about
5" contracted length.

I see plenty of springs on McMaster to choose from, but I'd like to be
able to order the correct spring the first time.

Thanks!

You want the spring with the lowest spring rate (pounds/inch) that
will support your load in the space available. Some of the spring mfrs
have selection tools online that make it easier to zero in on a spring
than McMaster. This will give you enough information to go back to
McMaster to see if they carry something close enough.

For example:
http://www.centuryspring.com/Century...ion_search.jsp

Associated Spring and Lee Spring are two other places to check.

--
Ned Simmons

On Mon, 14 Dec 2009 13:41:54 -0600, Pete C. wrote:

I need help in selecting an extension spring to counterbalance most of a
3.5# load over a hair less than 1" of travel. The 3.5# load needs to
rest solidly against the bottom stop at rest, and I need most of the
3.5# load counterbalanced through the 1" stroke, so it seems I need a
spring where the rate will not change significantly over that 1" travel.
I have a good amount of room to mount a fairly long spring, up to about
5" contracted length.

I see plenty of springs on McMaster to choose from, but I'd like to be
able to order the correct spring the first time.


Google "constant-force springs".

Good Luck!
Rich

Do a Google on springs. There should be some good design info there.

Bob Swinney
"Pete C." wrote in message
ter.com...

I need help in selecting an extension spring to counterbalance most of a
3.5# load over a hair less than 1" of travel. The 3.5# load needs to
rest solidly against the bottom stop at rest, and I need most of the
3.5# load counterbalanced through the 1" stroke, so it seems I need a
spring where the rate will not change significantly over that 1" travel.
I have a good amount of room to mount a fairly long spring, up to about
5" contracted length.

I see plenty of springs on McMaster to choose from, but I'd like to be
able to order the correct spring the first time.

Thanks!

On Mon, 14 Dec 2009 13:41:54 -0600, "Pete C."
wrote:


I need help in selecting an extension spring to counterbalance most of a
3.5# load over a hair less than 1" of travel. The 3.5# load needs to
rest solidly against the bottom stop at rest, and I need most of the
3.5# load counterbalanced through the 1" stroke, so it seems I need a
spring where the rate will not change significantly over that 1" travel.
I have a good amount of room to mount a fairly long spring, up to about
5" contracted length.

I see plenty of springs on McMaster to choose from, but I'd like to be
able to order the correct spring the first time.

McMaster has the pounds force and pounds/inch in there search
online. It should allow you to get close.

On Dec 14, 3:20*pm, Wayne Cook wrote:
On Mon, 14 Dec 2009 13:41:54 -0600, "Pete C."
wrote:



I need help in selecting an extension spring to counterbalance most of a
3.5# load over a hair less than 1" of travel. The 3.5# load needs to
rest solidly against the bottom stop at rest, and I need most of the
3.5# load counterbalanced through the 1" stroke, so it seems I need a
spring where the rate will not change significantly over that 1" travel.
I have a good amount of room to mount a fairly long spring, up to about
5" contracted length.

I see plenty of springs on McMaster to choose from, but I'd like to be
able to order the correct spring the first time.

* McMaster has the pounds force and pounds/inch in there search
online. It should allow you to get close.

A few years ago I designed a zero gravity simulator for the air
force. The concept is a hinged cantilever arm with a linear spring
attached between the end of the arm and a point equal distant above
the arm and directly above the spring. If the arm is horizontal from
the mount, the spring, arm and mount form a 45 deg triangle. Without
a weight on the arm it will spring vertical. If one adds an
appropriate weight on the end of the arm it is balanced by the spring
and will behave as gravity is gone. Alternately one can place a
pulley on the upper mount and install the spring in back. One way to
look at it is that it implements a zero stiffness or constant force
spring.

An other option to implement a low stiffness spring is to use a bucked
beam. Think of a yardstick pinned at both ends if on loads it above
the bucking load the yardstick deforms with a nearly constant force.

Pete C. wrote:

I need help in selecting an extension spring to counterbalance most of a
3.5# load over a hair less than 1" of travel. The 3.5# load needs to
rest solidly against the bottom stop at rest, and I need most of the
3.5# load counterbalanced through the 1" stroke, so it seems I need a
spring where the rate will not change significantly over that 1" travel.
I have a good amount of room to mount a fairly long spring, up to about
5" contracted length.

I see plenty of springs on McMaster to choose from, but I'd like to be
able to order the correct spring the first time.

Thanks!

Why not call a spring company and speak to somebody who knows springs?

There's one here called Stanley Spring and Stamping Corp.

"Pete C." wrote in message
ter.com...

I need help in selecting an extension spring to counterbalance most of a
3.5# load over a hair less than 1" of travel. The 3.5# load needs to
rest solidly against the bottom stop at rest, and I need most of the
3.5# load counterbalanced through the 1" stroke, so it seems I need a
spring where the rate will not change significantly over that 1" travel.
I have a good amount of room to mount a fairly long spring, up to about
5" contracted length.

I see plenty of springs on McMaster to choose from, but I'd like to be
able to order the correct spring the first time.

Thanks!

The best constant force spring is a air cylinder with a pressure regulator
suppling the air.
Constant pressure and no fatigue failures.

"Grumpy" wrote in message
...

"Pete C." wrote in message
ter.com...

I need help in selecting an extension spring to counterbalance most of a
3.5# load over a hair less than 1" of travel. The 3.5# load needs to
rest solidly against the bottom stop at rest, and I need most of the
3.5# load counterbalanced through the 1" stroke, so it seems I need a
spring where the rate will not change significantly over that 1" travel.
I have a good amount of room to mount a fairly long spring, up to about
5" contracted length.

I see plenty of springs on McMaster to choose from, but I'd like to be
able to order the correct spring the first time.

Thanks!

The best constant force spring is a air cylinder with a pressure regulator
suppling the air.
Constant pressure and no fatigue failures.
Apart from friction in the seals. Even on an oil hydraulics system. If you'd
ever tried it you'd know. A bellows or air spring would be better though.

On Tue, 15 Dec 2009 21:58:21 -0000, "newshound"
wrote:



"Grumpy" wrote in message


The best constant force spring is a air cylinder with a pressure regulator
suppling the air.
Constant pressure and no fatigue failures.

Apart from friction in the seals. Even on an oil hydraulics system. If you'd
ever tried it you'd know.

It's best to be sure of oneself when playing the know-it-all...

http://www.airpot.com/html/apply_precise.html

Frictionless and low-friction cylinders are also available from SMC.

--
Ned Simmons

In article , Cydrome Leader
wrote:

Pete C. wrote:

I need help in selecting an extension spring to counterbalance most of a
3.5# load over a hair less than 1" of travel. The 3.5# load needs to
rest solidly against the bottom stop at rest, and I need most of the
3.5# load counterbalanced through the 1" stroke, so it seems I need a
spring where the rate will not change significantly over that 1" travel.
I have a good amount of room to mount a fairly long spring, up to about
5" contracted length.

I see plenty of springs on McMaster to choose from, but I'd like to be
able to order the correct spring the first time.

Thanks!

Why not call a spring company and speak to somebody who knows springs?

There's one here called Stanley Spring and Stamping Corp.

Brriinnnngggg!!!

Recorded Voice: "Hello and welcome to the Stanley Spring and Stamping
Corporation, world's largest supplier of springs and stamps, where you
can find a spring or stamp to meet any need . . . ." followed by a
seven-minute, very detailed description of ALL their products.

Recorded Voice continues: "Please listen carefully. Our menu options
have recently changed. If you know your party's extension you can dial
it at any time. To speak to a sales representative, press 1. To check
the status of an order, press 2. To hear this message in Spanish, press
3. To speak to an account representative, press 4. If you want to
return an order, press 5. If you are an ISO government contractor
requesting a quote, press 6. If you'd like fries with that, press 7. If
you think I asked that question to see if you were paying attention,
press 8. To hear your menu options again, press 9. All others please
stay on the line and you will be connected to the next available
customer service representative."

[97 seconds of Muzak, probably Kenny G or John Tesh, or if it's
December, "God Rest Ye Merry Gentlemen."]

Garbled voice: "Thank you for kzzztt the Stanley Spring and Stamping
Corporation. My name is vvwwwyyttt. How may I bzzztt your call?"

You: "Um, yes. I'd like some information about spring specifications,
please."

Voice: "Do you have an account with us, sir?"

You: "Um, no. I just need some information."

Voice: "I see. What kind of stamp were you looking for?"

You: "Not a stamp. A spring."

Voice: "A spring?"

You: "Yeah. You sell those, don't you?"

Voice: "Yes, sir, and no need to get snotty, sir. What kind of spring
are you looking for?"

You: "I wasn't snotty. I was just making sure. I'm looking for an
extension spring."

Voice: "One moment, sir."

[more Muzak]

Voice: "All of our extension spring representatives are currently
helping other customers. If you wish to leave your name and number, and
the number of springs you'd like to purchase, in thousands, one of them
will get back to you right after their brea... er, as soon as possible,
sir."

You: "I don't want to buy thousands of springs."

Voice: [After a pause] "And, how many springs did you need, sir?"

You: "Just one, actually."

Voice: [After another pause] "Excuse me, sir, did you say one thousand
springs? One? Is that like the number one followed by three zeros, or
did you mean one hundred thousand?"

You: "I meant one. One spring. Singular. Maybe two if I decide to take
my project to the next level."

Voice: "Two thousand springs?"

You: "Sure thing, but first I just need the specifications so I can
order the right two thousand springs. Look, is there anyone I can talk
to about ordering the right spring? You see, I need a spring to
counterbalance a 3.5 pound weight over a distance of about 1 inch of
travel and I'm not sure . . . ."

Voice: "I don't know the first thing about springs, sir. I'm just the
receptionist, but I think I know someone who can help you. One moment
while I connect you."

[Muzak]

A Different Voice (huskier, lots of bourbon & cigarettes in its
history, noise of machinery in the background):
"Gunner here. Whaddya want?"

You: "Do you know anything about springs?"

The New Voice: "Hell YES! I know EVERYTHING about EVERYTHING! Except
Idaho. What do you know about Idaho? Did you know I was a cop? Say. . .
you aren't one of those pinkie lib fags are you? You didn't vote for
that scum Obama, did you? You wanna buy a used 9" Clausing? Hardly any
rust at all. Only take a month or two to scrape down the ways. Are you
a doctor? I might need another bypass and I'm looking to have it done
cheap. Don't worry, ObamaCare will pay big time and we can split what's
left over. . . ."

You: [Bangs head on desk.]


-Frank
(Just having some fun here. Slow day at the salt mines.)

--
Here's some of my work:
http://www.franksknives.com/