Yea, just sitting around on forums. 

Last night I wanted a spring for a hammer spring. One I had was too strong and the other too weak. I have some 1.5 mm wire, and it came out just exactly what I wanted, so you can judge by squeezing them, thickness of wire and length. The other factor is diameter of course.

Spring wire (piano wire)

Pliers

Cordless drill

small metal rod. (this determines the size of your spring

Bend about 15 to 20 mm end of wire 90 deg.

Put metal rod into drill, tighten, then slide bent end into the chuck.

Holding tight on the other end of wire with pliers, start drill slowly and let drill pull wire as you guide it.

Wire will be under tension, so carefully let it release when you finish.

It pays to make a mark on the rod for how long you want the spring so you know when to stop. Remember the spring will expend and be bigger than the rod you've wound it round.

Ends can be finished on a grinder to be made flat.

Give it a go, great fun. These springs were made from .8 mm wire, with the big one from 1.5 mm. It was my first attempt.