7 replies to this topic

[Silly]

So for one of my entries in the 2017 mod contest i need a spring longer and not too much wider or skinnier then a [k26], with just as much power behind it. I dont think i would be able to spring-merge two pieces of [k26] together, as i dont have acess to high strength adhesives or welding.

So, anyone know of any long [k26]-like springs available?

[thedom21]

There is a few on McMaster-Carr that should work, https://www.mcmaster.com/#9662K31 looks good.

 

In comparison to a [k26] it is 36" long while the [k26] is 11" long. The OD is 0.031" larger, ID is also 0.031" larger but it has the same wire diameter and they list the rate constant as 35.21 while the [k26] is listed at 42.69 so it would be a slightly lighter pull.

[Silly]

Sounds good! Im making the FOAP (The "Father Of All Pistols") for the mod contest, and i needed somthing long to be used in the massive plunger tube ive made.

[snakerbot]

Something to note about McMaster's rate constant. It's not the same thing as spring constant - the 'K' value we all know. Those springs are meant to be cut to length, which changes the spring constant, so you take the rate constant and divide by the length to get spring constant. For a full length [k26], this nets you a spring constant of 3.88lbf/in, and for the K31, that is .98lbf/in. The draw at maximum compression is probably in the same ballpark for each spring, which is probably what you want, but take this into consideration.

[Silly]

That is at full length of each spring, right? (Not cut down)

[thedom21]

snakerbot, on 24 May 2017 - 9:31 PM, said:

Something to note about McMaster's rate constant. It's not the same thing as spring constant - the 'K' value we all know. Those springs are meant to be cut to length, which changes the spring constant, so you take the rate constant and divide by the length to get spring constant. For a full length [k26], this nets you a spring constant of 3.88lbf/in, and for the K31, that is .98lbf/in. The draw at maximum compression is probably in the same ballpark for each spring, which is probably what you want, but take this into consideration.

 

I knew there was something I needed to do to those numbers to get a better comparison.

 

Silly, on 24 May 2017 - 11:01 PM, said:

That is at full length of each spring, right? (Not cut down)

 

How long of a spring were you planning to use?

 

9662K29 gets you a 3.806 lbf/in at a 0.75" OD and 0.54" ID so slightly smaller spring but draw would be very difficult on this one. Essentially the same as a [k26] but if you go longer it gets more difficult?

 

9662K44 gets you a  1.277 lbf/in with at a 0.75" OD and 0.59" ID which is a bit stiffer than the K31. Depending on how long you want the draw to be you should be able to pick one of these 3 to get a similar total draw weight of the [k26].

 

[k26] has a length of 11" Rate constant of 42.69 and spring constant of 3.88 lbf/in

 

For instance you could use 11" of the k29 and your rate constant would be 3.806 lbf/in x 11 in and your rate constant is 41.866 which would essentially feel the same as a [k26].

 

But you could achieve the same feel from a lot more spring with say a k44 where the spring constant is lower but the spring is over three times as long. Between the K29, K31, and K44 I would go with the K44.

 

         

[Silly]

I think i will go with the k44. I need about 3 full feet of draw for this monster, so that one should be good.

[Draconis]

Okay, clarification on how springs work:

 

For any given section of a spring, the same percentage of deflection requires the same total force.  Say I have an 11" spring which takes forty pounds of force to compress 90%.  If I cut it in half, that same 90% deflection will still require forty pounds to compress, even if that happens in 4.5" instead of 9".