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Old 12-20-2009, 11:51 PM   #1
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Talking spring rate ????

aloha all...is there a trick to find out what the spring rate is on different springs in lbs. I have a bunch of springs but don't know there rate (if thats the right term)
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Old 12-21-2009, 12:34 AM   #2
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Here is how I did it using a vernier digital caliper and a cooking/food weight scale which I had lying around. You need a steady hand to do this but

Set the caliper to the free length of the spring (its length without any load on it.) Place the spring vertically on the weight scale's measuring surface and then lower the caliper with its depth probe end first (with the caliper set to the spring's free legth) into the spring until the depth probe tip just touches the measuring surface. Then push down on the caliper a quarter inch (or some other suitable compression distance), which results in the spring being compressed by the same distance - read the weight scale at that compression setting. The spring rate is given by dividing the weight reading by the compression distance.

Perhaps someone has a more clever or easier way to find the spring rate (e.g. using known and precise weights to compress the spring while making a distance measurement.)
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Old 12-21-2009, 01:18 AM   #3
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Thanks zanglonli, your method works like a charm, measured a 17.5lbs spring as 18.0lbs, which is pretty close considering that it's quite hard to keep the pressure even to get a good reading from weights.

I imagine that it could be a bit more precise to use a fixed weight balast which you can put on top of the spring and have an opening in the middle where the caliper depth probe goes in. That way you also wouldn't need the weights each time once you know the weight of your balast piece.
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Old 12-21-2009, 04:06 AM   #4
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you can also rig up a G-clamp to compress your spring+scale into a bench and slowly wind it down measuring the heights and weights as you go.
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Old 12-21-2009, 07:42 AM   #5
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can I use a bathroom scale???it sounds like some weird math to me
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Old 12-21-2009, 08:14 AM   #6
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Quote:
Originally Posted by The Hawaiian View Post
can I use a bathroom scale???it sounds like some weird math to me
Yeah, but make sure that you subtract 10 pounds. Those things always make me fat.
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Old 12-21-2009, 09:24 AM   #7
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Do you know what manufacturer makes them? I have a bunch of sheets that I've collected specifying spring rates for various makes.
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Old 12-21-2009, 09:53 AM   #8
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If you have a local speed shop near by take the springs to them, They have spring rate compressors for checking the rates of valve springs though im not sure if it will measure something that light. give it a try they would probly try it for free
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Old 12-21-2009, 10:10 AM   #9
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Quote:
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Do you know what manufacturer makes them? I have a bunch of sheets that I've collected specifying spring rates for various makes.
me too...but I don't know the manufacturer, thats the problem
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