How to put a number on spring tension ?

[Milacron]

With gas springs I used to check tension by simply putting a digital scale on a drill press table and using the spindle rack as a sort of arbor press to press the spring against the scale. Worked great, but gas springs have consistant pressure, such that how far you compress it don't effect the reading much.

So how do you put a number on a regular coiled compression spring ? I've got a small one where it takes 1 oz of pressure to get it started moving a postage scale, 3 oz to move to half it's (at rest) length, and 6 oz to flatten it. So, what is it's "number" for comparison to other springs purposes ?

 

[L Vanice]

Don, you are asking about compression springs, but they don't have "tension."

Here is a link to answers to your question.
Compression spring specs

Larry

 

[deltaenterprizes]

I would use the weight to fully compress the spring.That was the way I was told to identify the strength of recoil springs for 1911 style pistols when I was shooting matches.
The method was to put a dowel in the spring,put a washer over the dowel,put assembly on a scale,push on washer to compress the spring and read the scale at full compression.
To compare springs ,check the diameter of the wire,thicker wire stronger spring,all other dimensions being the same.

 

[MattW]

Coil springs have a "spring constant" or "rate" in units like lbs/in or N/cm, etc., some amount of force per unit displacement. Normal coil springs should be pretty linear in the working range. So, if 1 lb deflects the spring 1 inch, 2 lbs should deflect the spring 2 inches.

When you are measuring this, maybe put your scale on your mill so you can get a more accurate deflection reading. Don't let your last reading be the full "flattened" position, commonly known as "stacked height". Put a little pressure on the spring, zero your press and scale, compress to some deflection short of stacked and read your force and deflection. Make sure your scale does not deflect. Maybe put a DTI near the spring and factor in any scale deflection. Divide the force by the deflection and that is your spring constant.

 

[3t3d]

The usual spec, is pounds per inch. Add in the pre-tension, and you have story.

The gas spring as you describe them, have a low pounds per inch, or rate. Since they don't increase much during the stroke. They do have mostly pre-tension, so they stay fairly constant.

Think about a mainspring, or window shade spring, it has a low "rate" but is pre-tensioned most of the way. this gives it a nearly constant tension in use.

Other special (coil) springs have a variable pitch in the windings. As the fine pitch coils stack up, the spring rate goes up, as the remaining wide coils have to move farther per inch of travel. These are commonly seen in suspension springs.

I hope this helps!

 

[gbent]

Gearheads use a spring tester. Think small arbor press with a weight scale built into the bottom. There is a rule attached to the bottom that allows one to read the height of the spring. Usually look for a minimium force for a given height.

 

[pistonskirt]

Gearheads use a spring tester

*LMAO*

Here is this old "gearheads" very old spring tester.

regards

Brian

 

[Forrest Addy]

Yup. Gas springs don't follow spring rate rules too well.

I think Matt has the right approach. Specify a gas spring in terms of the initial load (preload), the travel, and the full load just short of "two blocked".

 

[sneebot]

Are you looking for the spring constant? If so this can be calculated using F=kx where F=force, K=spring constant or rate and x=distance. You don't provide the overall length of the spring you are looking at...

 

[MitsTech]

D, it all depends on how you want to rate the spring.

For example, automotive valve springs are typicly checked at "installed height", meaning, if they are compressed .100" at rest, you would compress the spring .100" and check the force.

Basicly, you have to match the load to the application. If you need a spring with 500# of force at 50% compression, that's where you measure your force.

 

[Glenn Wegman]

spring rate calculation

I used to use a simple formula that was based on wire diameter and number of coils which worked well, but can't remember remember what it was!(long time ago)

Got it!!

Glenn