Measuring Spring Strength

[CDBPDX]

So a couple times I've refurbished the springs in broken machines and had this problem - the motor seems to work fine 'on the bench' but when I slap on a turntable and try to play a record, it slows down and stops. Like the drag of the needle in the groove was too much for the springs.

I assume the problem was weak springs because replacing them with new springs seemed to fix it. When I'm installing the 'weak' springs, there doesn't seem to be anything weak about them until it's time to play a record. Some folks feel all springs should be replaced with new ones, but I hate to waste a perfectly good used spring if it will do the job.


Is there a 'standard' for spring strength and a way to measure it besides install it and see if it works? Is there any way to tell if it is too weak?

Or do I just need more experience to recognize a weak spring when I see one?

CDB

[JerryVan]

CDB,

As you surmise, the real test of a spring is in trying to use it. Besides setting up a test stand, with a way to measure output torque for a given number of crank revolutions, then creating a "standard" by which to compare test samples, there really is no better way.

That being said, you can sometimes spot a "weakling" by observing the number of "loose" coils of spring as it spirals towards the center arbor. By loose coils, I mean sections of spring that are not wound, (or unwound), tightly against the next layer. So, if you see maybe 15 or 20 revolutions of spring, as it spirals in towards the center, that do not contact each other, versus maybe 3 or 4 such revolutions, you can bet that the spring with the higher count is weaker. Is it too weak? Don't know till you try it...

[CDBPDX]

CDB,

As you surmise, the real test of a spring is in trying to use it. Besides setting up a test stand, with a way to measure output torque for a given number of crank revolutions, then creating a "standard" by which to compare test samples, there really is no better way.

That being said, you can sometimes spot a "weakling" by observing the number of "loose" coils of spring as it spirals towards the center arbor. By loose coils, I mean sections of spring that are not wound, (or unwound), tightly against the next layer. So, if you see maybe 15 or 20 revolutions of spring, as it spirals in towards the center, that do not contact each other, versus maybe 3 or 4 such revolutions, you can bet that the spring with the higher count is weaker. Is it too weak? Don't know till you try it...

Thanks! That explains a lot. CDB