Advice needed: 91mm scissors in 84mm SAK

[ComboTool]

I have found several mods using 91mm scissors in 84mm SAKs, for example here or here. They all use an "old style" 91mm scissor backspring without the hook. While not as rare and expensive as 84mm scissors, these are quite difficult to find. Has anyone tried doing the same with a recent backspring?

[Max Stone]

Not tried but it should be possible as the part of the backspring you’re shortening is opposite the hook, and the 84mm back tools are the same dimensions as the 91mm. 

[tattoosteve99]

You can do it with either. It takes work. You can also use thinner springs and use two of them. There are many possibilities. I’ve done it with all but the new ones. I think it has been done before but not sure.

[kamakiri]

It should work, but will need a 4 pin construction.

[kamakiri]

It should work, but will need a 4 pin construction.

Since having done this different ways, the 4th pin is only required if the fixed end is a typical cut/slider type assembly. It is not required if the backspring is a single unit, not 2-piece construction.

[hulk.]

we can know the usefulness of the 4th pin please ?

[ComboTool]

If you look at a blade or opener layer (with tools on both ends and on the back), in a 3-pin construction there is nothing preventing the spring from moving or even "escaping". The 4th pins prevents this end-to-end motion.

[kamakiri]

If you look at a blade or opener layer (with tools on both ends and on the back), in a 3-pin construction there is nothing preventing the spring from moving or even "escaping". The 4th pins prevents this end-to-end motion.

  Exactly.

The separate scissor tip rest is like a ‘dead’ tool. It does nothing to prevent lengthwise movement of the backspring. That’s the job of the 4th pin when the 3 tool per layer function was introduced.

[hulk.]

it's true , I foolishly thought we were talking about a 5th pin  .

[kamakiri]

it's true , I foolishly thought we were talking about a 5th pin  .

LNFs and custom doodads. Good reason for a fifth.

Sorry for the confusion. Just wanted to clarify the point I was making before is only correct with certain stipulations.