Quote Originally Posted by Black Beard View Post
Spring constant is approximately (all dimensions mm and for steel springs):

10^7 * wire diameter^4 / (outside dia-wire dia)^3 / number of coils

to give the newtons per meter spring constant. Change 10^7 to 10^4 to give newtons per mm

so 2mm wire with outside diameter 22mm and 20 active links (ignore ends) is

10 000 000 * 16 / 8000 / 20 = 1000 Newtons per m or 1 newton per mm. Too weak for an air rifle. Most air rifle springs are 5000 to 12000 Newtons per m spring constant.

Thicker wire, lower diameter and less coils = stiffer.
For your formulas that model spring gun behavior...do you need this spring constant or is spring rate needed? Or both?

I have wanted to try this but never dealt with the tools involved. I have read about the shadetree method of putting a bathroom or other scale down on a surface or press and using that to measure the force.

But I'm reading about tools like these. Anybody use one? What pressure/force scale or rating would be appropriate for the springs inside a springer (a TX200 in this case). Seems like one of these in a vise or drill press (chuck a guide of some sort in the press and slip the spring over it) would do the trick.

http://iyrs.org/Portals/0/Uploads/Im...log2%20139.jpg
http://iyrs.org/Portals/0/Uploads/Im...log2%20141.jpg

http://www.youtube.com/watch?v=tVsrky0cpDs