lfw618
Mechanical
- Oct 4, 2018
- 61
I am designing a spring to be a replacement for existing springs. I have access to the existing springs and have tested them for load at height and measured key characteristics. I am working on a print to spec the springs to our vendor. It is a pretty simple/straightforward task, I'm just getting confused on specifics around the spring rate.
I am using the formula k=Gd^4/(8*N*D^3) to verify/validate what I am sending to the spring manufacturer. I have a couple options for how I can specify load. I can either specify loads at two heights, or specify required spring rate between two heights. I am confusing myself on what the above formula is determining, not sure if I am overthinking it. I am playing around with wire diameter, number of coils etc. so that I spec the right nominal values for our vendor accurately reproduce the spring.
I am not clear on whether the rate equation refers to the spring rate measured from deflection from free length, or deflection between two heights that are in the middle 60% of the spring.
I'll try to clarify my confusion with an example. I measured the springs at two heights, 1.39" and .98", and I measured the free height at 2.44" (1.042" avg coil OD .097 wire diameter for reference). The rate between the two heights is 32.3 lb/in. The rate at each height respectively is 30.3 lb/in and 30.9 lb/in when calculated from deflection from free height.
My confusion is whether that formula for rate, calculated the value to reflect the 32.3 value or the 30.3/30.9 values. Knowing that would help me to spec the correct# of coils and free length to our vendor.
Thanks in advance for your help.
I am using the formula k=Gd^4/(8*N*D^3) to verify/validate what I am sending to the spring manufacturer. I have a couple options for how I can specify load. I can either specify loads at two heights, or specify required spring rate between two heights. I am confusing myself on what the above formula is determining, not sure if I am overthinking it. I am playing around with wire diameter, number of coils etc. so that I spec the right nominal values for our vendor accurately reproduce the spring.
I am not clear on whether the rate equation refers to the spring rate measured from deflection from free length, or deflection between two heights that are in the middle 60% of the spring.
I'll try to clarify my confusion with an example. I measured the springs at two heights, 1.39" and .98", and I measured the free height at 2.44" (1.042" avg coil OD .097 wire diameter for reference). The rate between the two heights is 32.3 lb/in. The rate at each height respectively is 30.3 lb/in and 30.9 lb/in when calculated from deflection from free height.
My confusion is whether that formula for rate, calculated the value to reflect the 32.3 value or the 30.3/30.9 values. Knowing that would help me to spec the correct# of coils and free length to our vendor.
Thanks in advance for your help.