Slipjoint preload in spring?

[Taximanny]

I have watched and read a lot of tutorials on making slipjoints and have seen two different methods on the spring.

One, they preloaded the spring a couple millimeters by moving the back pin in the spring up.
And the others never mentioned preload at all and drilled and set both pins on the spring before HT.

Question is WHY?
What are the pros and cons of either method ???

Thanks
Manny

 

[Drew Riley]

You definitely want to pre-load your spring one way or another. I've noticed the same thing you have with tutorials, in that some makers make a point of mentioning, and other just seem to forget/gloss over it.

The first method you mention is a little more viable on wider handled slipjoints, or if you have extra material around your pin holes. I've found that for smaller/narrower framed knives, you don't really have a lot of extra room/material to move the spring out if going off of a pattern. Since I draw most of my patterns for slipjoints in autocad, I do things a little differently.
Obviously, when drawing a pattern, you can't really sketch in the pre-load (well, I guess you can, but the following is easier), so what I do is cut the "straight" template for my spring, and when I'm tracing it onto the steel, I'll trace and mark everything from the center pin down, and then before I scribe the top half, I'll pivot the top forward from the center pin, roughly about the width of the spring (this usually moves the rear of the spring about 1/16th of an inch or so, which is typical of the method you already mentioned.

What this gives me is a slightly canted forward spring that's essentially pre-loaded by design, but it allows me to keep my center and back pin holes in the same spot, per the original design. Make sense?

 

[Taximanny]

Read it a few times and still trying to take it all in.
But knowing I have to put preload in it is a relief.

So now I only have about 10 other things I can mess up at.
Thanks for the answers I have been looking for.
There will be more I'm sure of it.

 

[stezann]

Yep, preload is necessary and will be set accordingly to the beefiness of the spring and the distance between the central pin and the pivot.
The preferred method is moving up the final pin location (or lowering the central), better than yealding over the elastic modulus on ht'ed spring, but you can bend the untreated spring safely if you had already drilled without preload.