Originally Posted by
DaveW
Oh i understand perfectly. No need.
'... misinformation stating that only wire diameter will change the spring rate of a compression spring.'
To be sure we are on the same page, by spring rate, you are referring to the actual numerical value of the spring... right? To me it sounds like you are defining a compounding effect of compression.
That in turn sounds like you are telling me that ALL linear compression springs are progressive in nature? How is this so when the entire spring, regardless of how many coils are present, bears the same load (not to mention weaken as they are compressed... all flexible materials do, thats why materials like Delrin break, and steel bends)? All coils are 'active' once under load. They remain active as a unit (a singular unit) unless compressed as one (basically becoming a bumpstop).
You kind of lost me on that last paragraph. But what I mean by spring rate is the spring constant, k, a force constant which gives you the elasticity of the spring (usually in a lb/in or kg/mm rating in compression springs). This is linear because if you had a 2lb/in and compressed it 1 inch, the spring would be exerting 2lbs of force and if the spring were compressed to 2 inches it would exert 4lbs of force (perhaps thhis is what you were refering to by the "compounding effect"). Thus, the spring increases in 2lb increments for every inch = 2lb/in.
To take a stab at your last paragraph, the material shouldn't 'weaken' when compressed as long as the load does not cause the stress in the spring to go above the linear elastice region of the material, in which once it goes outside this region the material has plastically deformed and will no longer return to its original shape ( like when you stretch a spring too far and it doesn't go back to its originally shape). Additionally, if you stretch the material (spring) much further after this and the stress of the spring reachs the ultimate tensile strength of the material, then the spring will break. We don't usually see this in compression springs but rather may eventually fatigue a spring causing it to break, which is a result of imperections in the material or operating outside the range of the materials fatigue strength. Our springs we use in RC are also ground and squared end springs which results in the loss of 2 active coils (so they are not all active).