Technical specs of springs used in Stratocaster style trems?

[Neverwhere]

I'm building a tremolo unit from scratch that has a horizontal spring like a Strat trem, I'd like to use one single spring that is a little bit longer than the ones used in strat trems, I'm having difficulty finding technical specs of these springs so I can get in the right ballpark before ordering some varying tension springs for experimentation.

Anyone know how to find min/max load, wire dia, max extended length@load and rate of these springs?

 

[Timtam]

As you've noticed, no strat trem spring vendors I know of specify their springs' mechanical properties, like the spring constant (stiffness). Instead trem springs are often described by meaningless terms like "vintage". That also means that people are not encouraged to understand the simple mechanics of trem springs.

Your best starting point is perhaps the one or two companies that sell a range of trem springs: "soft"/"weak", "medium", and "heavy"/"strong"/"high" (most likely euphemisms for their spring constants). Then measure their spring constants yourself - it's a simple science experiment done in many high school science classes. Just measure spring tension (load) and length for several different hung masses as shown in this video. If you don't have known masses, a cheap digital luggage weight gauge and turnbuckle will work too. Then plot each pair of load and length values on a graph like that below.
www.youtube.com/watch?v=2kOtd69Uis4

Then you can measure any of the single springs available from many other vendors and tell which ballpark they fall into. If you do, please post your results back here - there is little such data available.

Also, understand the simple physics of spring constants. Particularly that they are additive. So removing one spring of four will reduce the overall spring constant by 25%. Or adding a fifth spring (of the same type) will increase overall spring constant by 25%. If you understand that, spring performance is predictable and thus easily manipulated - there is usually no need to try a different spring vendor (who probably won't even tell you or even know their spring constant), for an unknown result.

Of course the overall stiffness of a trem is down to the balance of spring stiffness and string stiffness. On a floating trem, the torque generated by the springs exactly balances the torque generated by the strings. But because the springs have a much longer moment arm (perp distance from block attachment to knife edge axis), their force (tension) is much lower than that of the strings.

Here's some example data on strat spring properties (from sookwinder at OSG forum). The spring constant (stiffness) is given by the slope of the tension (load) versus extension curve. The springs below are linear (like most springs) and have similar spring constants once under significant load, but quite different tensions at any given extension. However that difference is usually equalized in practice by the fact that the claw has to be tightened enough to bring the springs to the same starting tension, to balance whatever counter torque the strings are generating.

https://www.offsetguitars.com/forums/viewtopic.php?f=29&t=32609