SD aftermarket guide rod/spring analysis thread

[huafist]

So, based on the discussion we were having in this thread:
http://smith-wessonforum.com/smith-...-broken-frame-slide-takedown-lever-issue.html

I decided to start a new topic, as suggested by 3hounds. Based on our discussions, I actually ordered an SS guide rod from stainless steel guide rods, Inc on Amazon yesterday. I'm going to do some testing with the 20lb spring that comes with it, as well as the stock spring. I'll be checking:

1) Free length of each spring, as well as distance between coils uncompressed.
2) Distance between coils at install height.
3) Coil bind (stacking) on both springs.
4) If I have the time, I'll check preload and max compression load numbers.

 

[Steve912]

Include the thickness of the rod base also, in overall length of compressed spring stack.

 

[40s&w]

Who makes the springs for stainless steel guide rods Inc?

 

[3hounds]

Which guide rod did you order ?

Oh I see they actually make one for our guns, nice.

ISMI believed the Gock 19 guide rod and spring should work
in our guns.

Mine didn't as you know, spring is too long.

Thanks, 3

 

[Disabled1]

After a few months with the Galloway SS Glock 19 guide rod assembly in my SD9VE, I have shot WELL OVER 1K rounds of anything from 115 gr to 147 gr in it, and had NO FTE, FTF, or FTF's! I would have to say that installing the $12 cheaper in price Glock SS guide rod over the recommended $12 more required S&W SDVE SS guide rod assembly, was a great choice!

 

[ou1954]

Measurements

So, based on the discussion we were having in this thread:
http://smith-wessonforum.com/smith-...-broken-frame-slide-takedown-lever-issue.html

I decided to start a new topic, as suggested by 3hounds. Based on our discussions, I actually ordered an SS guide rod from stainless steel guide rods, Inc on Amazon yesterday. I'm going to do some testing with the 20lb spring that comes with it, as well as the stock spring. I'll be checking:

1) Free length of each spring, as well as distance between coils uncompressed.
2) Distance between coils at install height.
3) Coil bind (stacking) on both springs.
4) If I have the time, I'll check preload and max compression load numbers.

It would be beneficial to also measure the spring rate if you do have a decent scale and distance measuring tool. You might be able to derive it from the measurements you intend to make.

 

[Sidnne]

After a few months with the Galloway SS Glock 19 guide rod assembly in my SD9VE, I have shot WELL OVER 1K rounds of anything from 115 gr to 147 gr in it, and had NO FTE, FTF, or FTF's! I would have to say that installing the $12 cheaper in price Glock SS guide rod over the recommended $12 more required S&W SDVE SS guide rod assembly, was a great choice!

I shot about 1,500 rounds with the Galloway spring before my frame broke.

 

[huafist]

Include the thickness of the rod base also, in overall length of compressed spring stack.

Of course As well as the thickness of any washers at the other end of the rod.

 

[huafist]

It would be beneficial to also measure the spring rate if you do have a decent scale and distance measuring tool. You might be able to derive it from the measurements you intend to make.

I figured could get it using the spring rate formula
(k = (d^4G)/(8D^3N))

However, after a little time, it occurs to me that the guide rod springs are flat wire, not round. I don't think I can derive an accurate value for (d) in the above equation with flat wire?

***EDIT 2***
I'm an idiot. I can treat it like a rectangle and find it's diagonal length.

 

[4MUL8R]

There is a different formula for flat wire springs. If I hadn't turned in my mechanical engineering handbooks I would give it to you. You can measure load at two compressed lengths and obtain the rate directly. Keep in mind that as coils begin to touch that the rate can change.

 

[huafist]

There is a different formula for flat wire springs. If I hadn't turned in my mechanical engineering handbooks I would give it to you. You can measure load at two compressed lengths and obtain the rate directly. Keep in mind that as coils begin to touch that the rate can change.

Good to know. I'll see if the all-knowing google will turn up the rate formula for the flat wire coil spring.

 

[ou1954]

Spring Rate

Good to know. I'll see if the all-knowing google will turn up the rate formula for the flat wire coil spring.

No objection to scientific research [my old home] but I would be much more comfortable with direct measurements of real springs. I understand that someone in this thread is going to do that this weekend.

We know nothing about the characteristics of the spring material, so even with a perfect formula there are still many unknown variables.

ISMI says: "All Springs are Heat Treated, Shot Peened & Stress Relieved" so I'm not sure where that leaves us with regard to the material properties.

ISMI also seems to admit that spring characteristics do change with use, although probably not much in a gun, but of course, a lot in a race car.

 

[huafist]

No objection to scientific research [my old home] but I would be much more comfortable with direct measurements of real springs. I understand that someone in this thread is going to do that this weekend.

We know nothing about the characteristics of the spring material, so even with a perfect formula there are still many unknown variables.

ISMI says: "All Springs are Heat Treated, Shot Peened & Stress Relieved" so I'm not sure where that leaves us with regard to the material properties.

ISMI also seems to admit that spring characteristics do change with use, although probably not much in a gun, but of course, a lot in a race car.

I agree 100% ; I'm just curious as to how close the numbers in the real world are to what the math says they should be. However, instead of digging around looking for something that I may or may not find based on terminology used, I think we can agree that the best real world method is k=F/x.

I've already taken apart a stock guide rod and done some force measurements on it, and I'll do the aftermarket after it gets here tomorrow. Hopefully we'll find some useful data this way.

 

[TriumphMan]

? for the guru's.

A slide spring has 4 things going on.

1: preload

2: spring poundage/rate

3: over-all compression length

4: rebound

What point of a spring is measured to consider it's weight rating for a gun's slide?

What I mean, is the spring divided into sections for measurements? Like the first 1/5rd is your preload, then 1/5 to 3/4 of spring length is where poundage is measured and last 1/3 of spring the weight doubles, while not stacking, to build up compressed energy for the ejection and next round/feed rebound, while all the time also pushing the weight of slide back/forwards.

 

[huafist]

So, the SS guide rod came today:
[ame="https://www.amazon.com/Wesson-Stainless-Steel-Guide-Assembly/dp/B00Q5Y3ILI/ref=sr_1_1?ie=UTF8&qid=1466638445&sr=8-1&keywords=Guide+Rod+sd9"]Amazon.com : Smith and Wesson SD9VE/SD40VE Stainless Steel Guide Rod Assembly (Drop-in Ready!) : Sports & Outdoors[/ame]

In overall lenth, it's only .003" longer than the stock polymer rod - and that's at the captive screw, which sticks out of the slide anyway. Other than that, the dimensions are identical.
I installed the spring and checked slide travel - the slide stops in the EXACT same spot as it does with the stock rod. Travel is identical.
The spring is definitely stiffer than stock, but my scale gave up the ghost on me when I tried to measure it (it won't do anything now but put '8888' across the LCD).

At installed height, the air gap between coils was only .0005" difference from the stock spring, on the wider side.

I'm going to pick up another scale this week and hopefully get some better information for everyone over the weekend.

 

[huafist]

? for the guru's.

A slide spring has 4 things going on.

1: preload

2: spring poundage/rate

3: over-all compression length

4: rebound

What point of a spring is measured to consider it's weight rating for a gun's slide?

What I mean, is the spring divided into sections for measurements? Like the first 1/5rd is your preload, then 1/5 to 3/4 of spring length is where poundage is measured and last 1/3 of spring the weight doubles, while not stacking, to build up compressed energy for the ejection and next round/feed rebound, while all the time also pushing the weight of slide back/forwards.

While I'm not a "guru", the numbers crunching that I've done so far leads me to believe that's a full travel of the slide. I'll post numbers later to show my work.

 

[ou1954]

Spring rate

? for the guru's.

A slide spring has 4 things going on.

1: preload

2: spring poundage/rate

3: over-all compression length

4: rebound

What point of a spring is measured to consider it's weight rating for a gun's slide?

What I mean, is the spring divided into sections for measurements? Like the first 1/5rd is your preload, then 1/5 to 3/4 of spring length is where poundage is measured and last 1/3 of spring the weight doubles, while not stacking, to build up compressed energy for the ejection and next round/feed rebound, while all the time also pushing the weight of slide back/forwards.

Spring rate is simply the force required to compress the spring a specific distance and is, in our application, pounds per inch of compression. It is (almost) independent of how much it is compressed. Also, it applies to the spring as a whole, but one can also take measurements of intermediate sections of the spring and get the same result.

If the free length of a spring is 2 inches and a force of 20 pounds compresses it to a length of 1 inch the spring rate is 20 pounds per inch. If the spring "stacks" when being tested the result is meaningless.

I sometimes wonder whether the theory of "suddenly applied loads" comes into play in gun spring design. Look it up, it's an unexpected effect and something everyone remembers from most mechanical or stress classes. (We remember the result/effect but usually can no longer state the formula. I had to look it up.)

 

[huafist]

Spring rate is simply the force required to compress the spring a specific distance and is, in our application, pounds per inch of compression. It is (almost) independent of how much it is compressed. Also, it applies to the spring as a whole, but one can also take measurements of intermediate sections of the spring and get the same result.

If the free length of a spring is 2 inches and a force of 20 pounds compresses it to a length of 1 inch the spring rate is 20 pounds per inch. If the spring "stacks" when being tested the result is meaningless.

I sometimes wonder whether the theory of "suddenly applied loads" comes into play in gun spring design. Look it up, it's an unexpected effect and something everyone remembers from most mechanical or stress classes. (We remember the result/effect but usually can no longer state the formula. I had to look it up.)

Since I'm not a mechanical engineer, just a nerd - would that "theory of suddenly applied loads" work in the same manner as a non-Newtonian fluid? ie, the more suddenly force is applied, the stiffer the response?

 

[huafist]

Ok, so here are some numbers on the stock spring. I'll have to get another scale before I can go any further, as mine died during testing.

Overall free spring length: 4.996"
Spring installed height: 2.995"
Given that the slide travels rearward 1.885" at full recoil, that means the spring has a maximum compression of 3.886" during operation.

I took compression force measurements every 0.5" for the first 2" of spring travel - I couldn't go any further due to my scale issue. However, that's been enough to get some good data:

4.996": 0.0lbs
4.496": 2.1lbs
3.996": 4.1lbs
3.496": 6.3lbs
2.996": 8.6lbs

So this means that the preload on the spring is ~8.6lbs. We've worked it out to a spring rate of 4.1lbs, which gives us 15.93lbs at full recoil.

 

[ou1954]

Ok, so here are some numbers on the stock spring. I'll have to get another scale before I can go any further, as mine died during testing.

Overall free spring length: 4.996"
Spring installed height: 2.995"
Given that the slide travels rearward 1.885" at full recoil, that means the spring has a maximum compression of 3.886" during operation.

I took compression force measurements every 0.5" for the first 2" of spring travel - I couldn't go any further due to my scale issue. However, that's been enough to get some good data:

4.996": 0.0lbs
4.496": 2.1lbs
3.996": 4.1lbs
3.496": 6.3lbs
2.996": 8.6lbs

So this means that the preload on the spring is ~8.6lbs. We've worked it out to a spring rate of 4.1lbs, which gives us 15.93lbs at full recoil.

Very valuable measurements . . .

So, we've been discussing spring rate here and assumed it was in the range of 16-22 pounds per inch.

It now seems clear that when a vendor talks about a 16 or 22 pound spring it's clearly not the technical spring rate.

Any thoughts?