need source for long, weak compression springs
 

We are looking for compression springs that are thin gauge (<.06 wire diameter), weak (around 10-20 lbs spring rate constant), narrow (between .65 and 1.125 OD), and long (3 ft. or longer). McMaster doesn't have anything that weak. I've been looking all weekend. Any ideas for a source? Thanks!

Re: need source for long, weak compression springs
 

How about here? http://www.centuryspring.com/Store/s...essionlong.php

There are a lot of companies that manufacture custom springs to order, but be careful -- the lead time might be beyond what you can deal with (or even beyond what's legal as a VENDOR!)

Re: need source for long, weak compression springs
 

I think you may need to consider using extension springs instead, which will be easier to find in the given parameters and won't be as likely to buckle.

Re: need source for long, weak compression springs
 

With a spring like that, you will need something to stabalize it to kep it from buckling. You can often stack springs on a shaft or inside a reasonably good fitting shaft (you need some room for growth, but not enough to allow for a buckle). I would recommend that shaft if it is possible. When stacking the springs, if they do not have a stackable seat, you can put a washer between them and stack them that way.
Remember your spring calcs (or look them up). In a stack, 2 30lbs/in. springs stacked in series turn into a 2x long 15 lbs/in spring. I think you may find some of your criteria overconstrain what you can get in springs. For example, buying 18 (or 3 packs) of this spring from McMaster:
Steel Compression Spring Zinc-Pltd Music Wire, 2.00" L,.970" OD,.125" Wire
And stacking them around a telescoping tubes would result in a 36" long spring, but the rate would be about 5.5 lbs/in and this is using wire that is more than 2X your required wire diameter.
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I am not sure about your application, but you might want to look into a "Gas Strut" They are nice compression springs that do not buckle and can be found in about 36" length with around 16" of stroke. The ones I am seeing on McMaster Carr are around 25 lbs. of force. This is a bit higher than you were looking for, but I think it might be better than a stack of springs and washers on telescoping tubes.

Re: need source for long, weak compression springs
 

We are using the springs inside telescoping tubes. We are also considering gas springs, but would need two or more in a stack to compress down to our required height (29") and extend as far as we need them to go (70"). The springs can be weak, as they only will be lifting about 2 pounds of telescopic tubing and a hook. Thanks for your ideas and input!

Re: need source for long, weak compression springs
 

I've used tall sprinkler head popup springs before that sound like they might work for you stacked.

Re: need source for long, weak compression springs
 

Really? 70" seems like a lot. If you really need this much extension, I can get you information on how to do it; but I am curious to know what this is for, if you don't mind telling.

Re: need source for long, weak compression springs
 

It's really just about 55" inches from the base of the bot (where the springs will start) to the end of the telescoping arm(s), where a hook will be located. The 70" allows for full extension without losing any force at the end. Happy to share our ideas. We are building two bots right now, one is a "normal" driver/shooter, the other a dedicated climber. Two extending hook "arms", two stationary hook "feet". In theory it works for any height. In practice, we having difficulty finding a few of the parts we want.

Re: need source for long, weak compression springs
 

Try cannibalizing a floor to ceiling shower caddy. The compression strut contains a long low rate spring within the 1" tube.

Re: need source for long, weak compression springs
 

You can pretty easily make springs from wire. Choose a pipe (PVC or steel) of somewhat smaller diameter than the final spring diameter. Mark with pen or chalk the disire spiral (pitch). Wrap wire tightly around the pipe. I put the pipe in my lathe and turn the pipe while guiding the wire.

Re: need source for long, weak compression springs
 

What kind of wire

Re: need source for long, weak compression springs
 

Is there a gag shop, magic shop, or clown supply store near you? The type of spring you describe is sometimes used in gag devices. Such as the fake can of nuts that contains several spring loaded fake worms that jump out. I am not sure if that is exactly what you are looking for, but it might be close.

I used to live near a magic shop and would occasionally go in looking for something like this for non typical applications. On one visit the woman at the counter looked at me a bit puzzled and asked, "Are you a clown"? The question did not take me completely off guard. You would be surprised how often women ask me that. But it was not for a while that I realized why this particular woman had asked. It turns out that they give a clown discount!

By the way, music wire from hobby shops make a serviceable custom wound spring, but the length is limited. You can sometimes also just over stretch an extension spring to convert it for compression use. You can also sometimes rewind a spring with the right sized wire into a new diameter and length if the original was not wrapped too tightly. Just be careful springs can be dangerous.

Re: need source for long, weak compression springs
 

Piano wire, coat hangars, MIG wire...

Re: need source for long, weak compression springs
 

For a spring? Yikes.

Re: need source for long, weak compression springs
 

Thanks for the ideas, especially the shower caddy. I don't think we will custom "wind" springs, though; compression springs are extruded, I think.

Re: need source for long, weak compression springs
 

Piano wire is "spring steel". Any metal can be used for a spring as long as the deflection doesn't stress the steel beyond yield strength.

DIY: http://zedomax.com/blog/2009/12/01/m...-from-scratch/

Re: need source for long, weak compression springs
 

I believe the "yikes" was for coat hangers.