DIY spring tester

[BK911]

I was thinking of ways to make a spring tester and wanted to see if anybody else has come up with anything.

My first idea simply involves a nut, bolt, washers, bench vise and torque wrench. Insert a washer, spring, washer then nut onto a bolt, then insert into a vise. Torque down until the required deflection and measure the torque required. This torque can be translated with some basic equations to give force, and you already know the deflection. Viola, spring constant.

Less than $1 in parts. But would it be accurate enough? The friction on the threads would have to be guestimated, but with graphite maybe it could be assumed negligible?

It's not that I'm looking for a cheap way out but IF the same results can be had for a fraction of the cost, why not?

[orbmedia]

Not the way to go. I think this would be extrememly inaccurate because of the friction losses involved. Don't do it by measuring torque and back-calculating. Instead just put the spring on a scale and sit on it and measure the deflection. The fatter you are the more deflection! Get your spring rates that way.

[911pcars]

If it's a valve spring, remember to position a board or some other posterior protection before sitting on it.

What was the rough calc for measuring suspension spring rate? Add weight to vehicle until the chassis drops 1", then measure the weight?

Sherwood Lee

[thabaer]

I've actually pondered in the past just for fun how to do this. (what's with MY brain?)

I always pictured a lever arm for a multiplier that would also give you an expanded scale to measure the deflection. You could even just set the whole rig on a concrete floor, anchor the fulcrum at one end of the arm, position the spring at 1:4 (or whatever ratio), then hang weight at the other end and measure. As long as the arm was rigid (or you measure it's deflection with a rigid block in place of the spring), it should be accurate.

[BK911]

Gentlemen!

Thanks for the input! I agree the friction value would be hard to estimate. Maybe get one spring checked at a shop, the put it on my contraption to figure out friction losses? Of just admit defeat and spring for the tester? Yes, pun intended!

The lever method would probably yield the best results. Back to the drawing board!

BK