Monster XL: I'm halfway there!

[sbell25]

I think there's a bit of confusion here. I think SilentGuy was actually referring to extension springs, however the problem here is compression springs so cutting it shorter is the right way to go.

I might have to try something like this as well, as I lost one of the springs and a plastic stopper for my 2700. The nozzle selector still works but not as well as it used to.

[Chewie]

The problem appears to be that the nylon stopper I made is JUST wide enough to hang up in the little socket it is in, so I'm going to need to take it out and shave it at some point. Not today, though

[Silence]

Originally Posted by sbell25

I think there's a bit of confusion here. I think SilentGuy was actually referring to extension springs, however the problem here is compression springs so cutting it shorter is the right way to go.

Well, it depends. Ben's right.

Hooke's law says F = k * d, where F is the force, d is the distance the spring is stretched, and k is a constant. It doesn't matter which way d goes, as long as the spring was designed to stretch that way.

But the formula also applies on a smaller scale - say, for each individual coil. A long spring has many coils, and if it's stretched a certain distance, lots of coils will stretch just a bit. That little bit of d for each coil means only a little bit of F is exerted in each coil. (Note that the overall force for the entire spring is not the sum of the F for each coil.)

With a shorter spring, there are fewer coils, so each coil must stretch more if you extend the spring by the same length. That means each coil exerts more force. The overall k, or force per distance stretched, is greater.

So cutting the spring could mean the spring will exert more force. But Ben's right in that if you cut it the right amount, the spring will need to be stretched so much less that the final force is less anyway. It's a balancing act, and unless you do calculations by counting coils, who knows what the result will be.

Anyway...

Good luck with your repair! I probably overanalyzed the situation, so no worries. Sorry for hijacking the thread.

[Ben]

If you want to be exact, but not use much math, here's a neat calculator I found at a Nerf forum a while back: http://www.engineersedge.com/spring_comp_calc_k.htm

This might be helpful for some other recent threads (the trigger springs one comes to mind).

[Silence]

At some point we could perhaps write an article to accompany the link to that spring forces calculator. Calculating values for materials and common sizes, perhaps with McMaster-Carr part numbers, could be invaluable and could help people trying to use the calculator. Still, approximation may take one far enough.

And there's some ubiquitous encyclopedia of materials, whose name I've forgotten, that contains precise statistics for every compound and mixture you can think of. You may have used it, Ben.

[sbell25]

Ben and SilentGuy, thanks for the info.

SilentGuy, I have to admit your answer left me a bit stumped for a while! You are right that cutting a spring increases it's rate. However when it comes to compression springs, no matter how short you cut it, and much you compress it by, the total force will always be less. Extension springs work opposite to this. Cutting an extension spring shorter increases it's rate AND total force.

I tested this by using the calculator than Ben provided the link to. For the purpose of experimentation the number of coils can be equal to the spring length in cm, inches, or whatever.

Now imagine that you have 2 compression springs. Both are identical except for length, and therefore the number of coils. Their lengths can be any number. Pick any number lower than the length of both springs. This will be the length the spring gets compressed to. Multiply the rate of the spring by the amount of deflection both springs are subjected to. You'll find each time that the total force will be less. Here's an example using the calculator:

Spring 1: 10 coil spring, 10" long, 10lbs/inch rate
Spring 2: 8 coil spring, 8" long, 12.5lbs/inch rate

Length when compressed in nozzle selector: 6" long.

Spring 1 Deflection: 10 - 6 = 4 inches
Spring 2 Deflection: 8 - 6 = 2 inches

Spring 1 Force: 4 * 10 = 40 pounds
Spring 2 Force: 2 * 12.5 = 25 pounds

As I said, that's just an example. Substitute any numbers you like in there, and the result will always be the same.

Hope that isn't too off topic.

Chewie: I'm interested in how you ended up making the stopper. Would you be able to take a photo of it?

[Silence]

You may be right. My assumption was that the spring will still be compressed the same distance after cropping it. But if it is only compressed to the same length as the longer spring is, then the total force may be less.

So if you use a spacer to compensate for the shorter length after cutting, then the force will be stronger for the shorter spring. But if you just go by the actual length, which I didn't consider, then you're absolutely right.

[sbell25]

Ah! I see what you're talking about. I hadn't even considered using a spacer, I just assumed that you would cut it to a length that was longer than the minimum required. So: if you're compressing the spring by the same amount, then yes, the shorter spring will have more force because it has a higher rate. However if you compress it to the same length, then the longer spring will have more force.

[Silence]

That is a more straightforward way of explaining it. Hooke's law (F=kd) really is rather simple, but it's easy to misinterpret what the d stands for. The d does stand for the length you stretch the spring by, not what you stretch it to.

Although you did bring up a good point that no matter what, a cut spring will always exert less force at a certain length than before. I hadn't realized that before.

[Ben]

At some point we could perhaps write an article to accompany the link to that spring forces calculator. Calculating values for materials and common sizes, perhaps with McMaster-Carr part numbers, could be invaluable and could help people trying to use the calculator. Still, approximation may take one far enough.

And there's some ubiquitous encyclopedia of materials, whose name I've forgotten, that contains precise statistics for every compound and mixture you can think of. You may have used it, Ben.

That might be a good idea. For some articles, I start their pages and outline my thoughts so I could add them later. You seem to know a good deal about springs, so that might be something you could start. I've found that half the work is the outline and making pictures if you want to use some.

I haven't run into any encyclopedia of materials, but if I do, I'll let you know.

Edit: Wow, this seems a little weird because I was replying to something SilentGuy said above. I need to refresh my pages I suppose.

[Silence]

I find myself having to hit Ctrl+Shift+R to reload and skip the browser's cache. I feel the quick reply box, which uses client-side scripting to display your post once you submit, is a bit buggy since it doesn't fully communicate with vBulletin with posts.

I'll ask my dad about that book tomorrow. It's been around in various editions for decades and is at least 1000 or 2000 pages thick, by the way.

[Chewie]

It mostly works, I'm still trying to get the spring fine-tuned. So you're saying that in the nozzle with the leak, the spring is pushing the stopper out too far, which is allowing water to come out the bottom hole.

Right?

[Silence]

Where are the O-rings in the nozzle/assembly? Around the hole in the main water gun? Obviously it can't just be around the entire spinning piece, as the water would then be able to escape from all the nozzles. I may take a look at my CPS 4100 to check.

You may want to try pressing on the rotating part in various places to see if that fixes the seal. Also, does the leaking happen regardless of which nozzle you use? Smaller nozzles have more plastic area exposed to the water, which means there's more force pressing on the turret.

[Chewie]

Originally Posted by SilentGuy

Where are the O-rings in the nozzle/assembly? Around the hole in the main water gun? Obviously it can't just be around the entire spinning piece, as the water would then be able to escape from all the nozzles. I may take a look at my CPS 4100 to check.

You may want to try pressing on the rotating part in various places to see if that fixes the seal. Also, does the leaking happen regardless of which nozzle you use? Smaller nozzles have more plastic area exposed to the water, which means there's more force pressing on the turret.

The leak only happens in the nozzle with the store-bought spring, I havn't thought to switch one nozzle with the other, so I don't know if that is a factor. I'm not entirely sure what an o-ring is in this context, but I know there is no damage to the nozzle piece.

[Ben]

If the Monster XL's nozzle assembly works similarly to the CPS 2700's, the spring can't push it out too far. In my CPS 2700, the maximum distance the nozzle assembly can move out is limited by a screw in the center. Perhaps you need to adjust this screw until it is at the correct distance.

The link below is a picture from a CPS 2700 showing the O-ring in the nozzle assembly. If your Monster XL is lacking something like this it won't seal correctly. Since you said there's no damage it probably isn't lacking this but it's good to check.

http://web.archive.org/web/200209180...r/cps27005.JPG

Edit: Me checking back to the beginning of this thread verifies that there is a screw that can be adjusted.