 Checking spring rate, Am I doing it right? |
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| bondo |
 Jan 8 2006, 09:17 PM
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#1
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Practicing my perpendicular parking  Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California  |
I set the spring with a metal plate on it next to a wall. I made a mark on the wall at the top of the plate. I added 25 lbs, 50 lbs, and 230 lbs (me), and marked the wall accordingly. I then did the math to calculate pounds per inch, and I get around 120 lbs per inch. (for example, it deflected 1.9 inches when I stood on it)
All the measurements started with a nearly completely unloaded spring, which is not the situation it will see in a car. Is the spring effect linear, or do I need to install them in a 914 and see how much it dips when I jump in the rear trunk? |
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| SirAndy |
Jan 8 2006, 10:38 PM
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#2
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Resident German Group: Admin Posts: 41,625 Joined: 21-January 03 From: Oakland, Kalifornia Member No.: 179 Region Association: Northern California |
find someone with a spring tester ... rich at HPH has one ... (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif) Andy |
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| bondo |
Jan 9 2006, 10:00 AM
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#3
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Practicing my perpendicular parking Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California |
(IMG:http://www.914world.com/bbs2/html/emoticons/icon_bump.gif)
Can anyone at least tell me if I'm way off? Or suggest a closer spring tester? (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif) |
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| Borderline |
Jan 9 2006, 10:09 AM
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#4
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Senior Member Group: Members Posts: 720 Joined: 8-February 05 From: San Juan Bautista, CA Member No.: 3,577 Region Association: Northern California |
That's the principle. You should be in the ball park. Make sure the spring is linear...All the coil spacing is the same distance when unloaded. I have a set of springs with 3 coils that are wound very close and actually go solid when installed in the car. That changes the rate. I think they did that so the spring wouldn't fall loose when the car was jacked up as it often is. Good luck. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)
Bill |
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| bondo |
Jan 9 2006, 10:26 AM
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#5
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Practicing my perpendicular parking Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California |
The coil spacing is even. I was expecting 180, which is why I ask. |
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| Aaron Cox |
Jan 9 2006, 10:35 AM
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#6
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Professional Lawn Dart Group: Retired Admin Posts: 24,541 Joined: 1-February 03 From: OC Member No.: 219 Region Association: Southern California |
my afco coils say they are tested this way:
compress spring one inch. now measure how much it takes to deflect the second inch..... |
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| bondo |
Jan 9 2006, 11:01 AM
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#7
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Practicing my perpendicular parking Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California |
Aha! Ok, I'll try that. Thanks! |
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| ppickerell |
Jan 9 2006, 11:29 AM
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#8
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914 addicted Group: Members Posts: 1,679 Joined: 14-October 03 From: Pleasanton, CA. Member No.: 1,246 |
Aaron is right. Get the spring under some load at somewhere around 15% of the available travel. Record the load value(L1). Deflect one inch and record the load (L2). Subtract Load 1 from load 2 and multiply by 10. You don't want to measure rate in the first 15 or last 15% of available travel.
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| bondo |
Jan 9 2006, 11:38 AM
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#9
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Practicing my perpendicular parking Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California |
Why multiply by 10? |
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| blitZ |
Jan 9 2006, 12:09 PM
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#10
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Beer please... Group: Members Posts: 2,223 Joined: 31-August 05 From: Lawrenceville, GA Member No.: 4,719 Region Association: South East States |
It's a 10 inch spring? |
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| ppickerell |
Jan 9 2006, 12:27 PM
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#11
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914 addicted Group: Members Posts: 1,679 Joined: 14-October 03 From: Pleasanton, CA. Member No.: 1,246 |
Ooops, My bad, the springs I make are so f'in small we travel them .100 inches and multiply by 10!
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| bondo |
Jan 17 2006, 04:17 PM
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#12
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Practicing my perpendicular parking Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California |
Ok, I tried it with more weight. I added weight in 50 pound increments, up to 300 lbs. I got more than 2" of compression. It looks like it's pretty linear.. I even graphed it. These are supposed to be 180 lb springs, what do you guys think?
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| Mueller |
Jan 17 2006, 04:31 PM
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#13
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914 Freak! Group: Members Posts: 17,146 Joined: 4-January 03 From: Antioch, CA Member No.: 87 Region Association: None 
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besides the fact that you are a geek??? (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif) looks like you are on the right track.... my method (I am not an artist) Attached image(s) 
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| bondo |
Jan 17 2006, 04:53 PM
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#14
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Practicing my perpendicular parking Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California |
I have a pic to post when I get home.. You WILL laugh. That is what I did, but it wasn't nearly as elegant. Besides my geekiness, doesn't it look more like a 120-130 lb spring than a 180? |
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| Mueller |
Jan 17 2006, 04:57 PM
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#15
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914 Freak! Group: Members Posts: 17,146 Joined: 4-January 03 From: Antioch, CA Member No.: 87 Region Association: None
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when I tested my springs ( a few different pairs), it seemed that with the correct amount of weight applied, the spring actually compressed a "tad" (1/4" or so) more than 180/1" or 360/2" |
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| bondo |
Jan 17 2006, 05:29 PM
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#16
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Practicing my perpendicular parking Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California |
Hmm, 1/4" would put it right in the 180 lb ballpark. Why would 180 lbs per inch really be 180 lb per 1.25 inch? |
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| bondo |
Jan 17 2006, 06:59 PM
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#17
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Practicing my perpendicular parking Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California |
I think I may have figured out where the 1/4" comes from.. one of the things you do when calculating spring rate is count the "free coils". Setting the spring on something flat gives it more free coils than when the top and bottom most coils are more supported by the spring saddle and hat. If I can figure out a way to do it, I'll try again using the spring saddle and hat.
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| bondo |
Jan 17 2006, 07:28 PM
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#18
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Practicing my perpendicular parking Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California |
Ok, here's the pic.. this is 300 lbs. Half the pipe is pounded into the ground. (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)
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| bondo |
Jan 20 2006, 06:19 PM
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#19
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Practicing my perpendicular parking Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California |
Ok, I measured the spring and used this formula to calculate the theoretical spring rate. (theoretical because not all alloys that are used for springs are the same) It comes out to 160 lb/inch. It also can't be exactly accurate because I measured the paint, which has some thickness.
Of course I'm not the type to be satisfied by math.. so I rounded up a spring tester.. of sorts. The displacement accuracy is .001.. the force accuracy is 1%. This is the sort of thing that satisfies me. (IMG:http://www.914world.com/bbs2/html/emoticons/happy11.gif) Attached image(s) 
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| bondo |
Jan 20 2006, 06:22 PM
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#20
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Practicing my perpendicular parking Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California |
Here is the graph of the data. (I did the graph a little differently this time.. makes more sense this way.. displacement vs. force) I tested both springs, as a double check. There's no way around it, this is a 140 lb spring.
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