The greater the winding ratio (average diameter/wire) the better.
No extremely high pitch because the spring cannot maintain its height
If the winding diameter is large, the pitch can also increase, this has to do with the angle of inclination of the winding.
Compare springs with the same spring rate and the same length and working length, but big difference in lifespan
Spring 1 in 3 mm and spring 2 in 1 mm have the same force.
Feather 1
Wire 3 mm SH spring steel
Outer diameter: 30 mm
Length: 100mm
Working coils: 12
Working length 1: 80 mm
Working length 2: 60 mm
Spring rate: 3.5N/mm
Tension at F1: 206 N/mm²
Tension at F2: 412 N/mm²
Permissible tension 1099 N/mm² so perfect
Goodmann Lifetime Chart >10 MIL Cycles
Suppose we don't have much space but the spring must have the same length and working length and the same spring rate as above, the outer diameter only 9.6 mm.
Veer2:
Wire 1.25 mm SH spring steel
Outer diameter: 9.6mm
Length: 100mm
Working coils: 12
Working length 1: 80 mm
Working length 2: 60 mm
Spring rate: 5.27 N/mm
Tension at F1: 944 N/mm²
Tension at F2: 1888 N/mm² (-> Much too high)
Permissible stress 1099 N/mm² so heavily overloaded and will break immediately
Council: the more wire length in the spring the better.
The condition of a German loop is that the hook length of the loop is 0.8 to 1.1 the inner diameter.
