What do back springs do in a slip-joint knife?

[Will Power]

Well, the French have been doing file-work for 2 centuries and more and I've never had a Lag or any other French knife break on me It obviously takes special skills.

 

[Misplaced Hillbilly]

Personally I'm not a fan of file worked springs. Back when I was working and making springs I learned that any marks on a spring, even a small scratch, can be a place of weakness, and the most obvious failure point. The better the finished surface of the spring before heat treat, the better the spring. Cutting a spring after heat treat is a bad idea. Flat springs should always be polished along their flex line.

Well, the French have been doing file-work for 2 centuries and more and I've never had a Lag or any other French knife break on me It obviously takes special skills.

Both these points are valid, I've often wondered why a worked backspring doesn't immediately give ip the ghost. The only way I can figure it works at all is the worked side is the compression side of the spring. I am also more leery of a spring that has been filed after the knife was made. However having said that I have a Camillus that has some basic file work that was done post production. It seems to do just fine.