Which of the following expressions is used as Wahl's factor for design of closed coiled helical springs?
(where, c is spring index)
1
\(\frac{{4c - 4}}{{4c - 1}}\)
2
\(\frac{{4c - 1}}{{4c - 4}}\)
3
\(\frac{{4c - 1}}{{4c - 4}} + \frac{{0.615}}{c}\)
4
\(\frac{{4c - 4}}{{4c - 1}} + \frac{{0.615}}{c}\)