Compression springs and extension springs

It's a bit difficult to follow you. I assume that the compression spring will be compressed from their rest position, and the extension spring will be arranged to somehow keep the compression springs from springing back to rest position, correct? What we would need to know is how far are you planning to compress the compression spring set, and then we can tell you how much the extension spring must be extended to counteract them. For example, if you want the compression springs to be compressed by 1.1 inches, this requires a force of 1/3 of 1.95 pounds = 0.65 pounds. This load can be generated by the extension spring if it is stretched 0.65/6.05 = 0.11 inches.

I have taken the liberty to copy the personal message you sent me here, as you should always post follow-up questions to the forum as opposed to using personal messages.

First, 3 springs in a row together act as spring that is 1/3 as stiff as a single spring. The formula for calculating spring loads is F=kx, where k is the spring coefficient in pounds/inch and x is the spring displacement from rest in inches. This formula assumes a perfect linear relatoinship between force and displacement - in real life this may not be the case, especially if the springs are compressed to the point where the coils begin to interfere with each other, or if a spring is stretched so far as to take on a permanent stretch.

From the data you have provided, the spring coefficient for the 3 springs stacked together and in compression is 1/3 of 1.77 pound/inch, or 0.59 pounds/inch. Since you want to compress the stack by 6.5 inches from a rest length of 9 inches to a compressed length of 2.5 inches, that requires 3.84 pounds of force. The extension spring has a spring coefficient of 6.05 pounds/inch, so it must be stretched 0.64 inches in order to balance the force of the compression spring.

One other item - you don't mention how the extension spring and compression springs are connected to each other - if through the trigger then is the trigger acting like a lever, with a center pivot and the springs attached at either end? If this is the case then the relative lengths of the two lever arms will affect the answer. Hope this helps.