How to Measure Strength of Small Springs?

"Doug White" wrote: (clip) For the extractor, I was thinking of comparing their strength by stacking

^^^^^^^^^^^^^^^^^^^^ That method should work, to give you comparative values. If you want real spring constants, you could measure their length with a pair of calipers while hanging a weight from one end. The spring constant should be the same for extension as compression.

To get a spring that does the job, you could rotate it lightly against a belt sander to reduce the cross section of the wire, and measure your progress with the "Doug White Screw Compression Method. Having a spring "in series" with it that remains unaltered, and which is compressed the same amount every time will enable you to see how the spring changes as you lightly sand off metal.

This is one type of device used to test springs. It wouldn't be too difficult to scab together something functionally equivalent in a drill press or small arbor press.

I don't have the articles handy, but if someone else from the group can check the May and July 1987 issues of the Home Shop Machinist, there was a detailed article on coil spring making. I would not be surprised if there was a section on measuring the results, but I don't have the articles readily at hand to check.

RWL

I did something a whole lot simpler: I cobbled up two chopsticks, one fixed, one (above the other) hinged. I put one spring between the sticks at a marked point and hung a little weight off the end, and measured the deflection. Then I put the other spring in and did the same thing. I never measured the spring constant, but I knew for sure which spring was stiffer.

GWE

Ned Simm> >

Hi Doug

It can be easy to measure spring constant with a weight measuring scale and a distance measuring ruler. You could probably get good enough accuracy of the "weight needed" to compress your springs some "given distance" by placing the spring on a postage scale of the appropriate sensitivity and push down on the spring . First, force the spring to move some small distance and record a weight and a length reading. Then add some force to compress the spring a little more. Those force and length numbers provide all the data needed to identify "Pounds per Inch" of each spring.

Jerry .

Jerry

"Jerry" wrote: (clip) You could probably get good enough

^^^^^^^^^^^^^^^^^^^^^^^ Theoretically. What will actuaqlly happen is that there will be too much vibration. Both the length and the force will be bouncing around so much you won't get good readings.

why not put a valve on your gas port?

My FN-49 has an adjustable gas port, and I can park the brass at my feet, or hurl them into the sun.

Gunner

Or stick on a brass deflector. They are legal under NRA rules

Gunner, jonesing for an M1A, really really bad. And they are legal here in Kalifornia.

Anyone want to trade one for machine tools?

Hi Leo

You are probably right, or why would you write about vibration. But, I have measured alot-alot of automotuve suspension springs exactly as I tried to outline.

Jerry

On Sat, 12 Jan 2008 08:19:08 GMT, with neither quill nor qualm, "Leo Lichtman" quickly quoth:

You'd get bounce on a balance scale, but not on a digital, pressure-sensing type. Use ACME/SAE screw holddowns vs. your hand for providing the down-pressure and it'll be clean. Whooee, ah gare-on-tee.

--- Chaos, panic, and disorder--my work here is done.

I was thinking about this, but in one case the spring is too short to work with easily, and in the other, it's too long and flexible to keep straight. I like the idea of adding a weight & measuring extension if I can figure out a good way to hang on to each end.

Thanks to everyone for all the good ideas!

Doug White

I thought about that, and there are aftermarket gas tubes with valves built in. That would require a fair amount of disassembly to retrofit. I've also heard that the gas tube valves can get clogged up & are a royal pian to clean. I figured I'd fuss with the springs first & see how it works out. It only takes a couple minutes to pull the bolt & disassemble it completely so it's an easy thing to do.

Doug White

Both rifles are flat tops, and have side cocking handles that will probably require a custom deflector design. The side cocker is needed because the adjustable butt stock has a raised cheek piece that interferes with the standard charging handle:

Doug White

Side cocking handle? You just had to be different huh...

Gunner