Blade Kick

[just bob]

OK, I have seen these forums where they detail the process of restoring kick to a blade and backspring that have excessive wear. What I would like to know if you're working with a knife that has a broken backspring and a broken blade and you have to replace both of them what is the process of establishing kick to the blade. If you search for this on Google you will see where they say this is a very complicated geometric formula. There must be some way that when you match the blade and the back spring up that determines the kick. If anyone has seen a good link on this subject just refer me to it and I'll read up on the subject. Many thanks.

[knives-are-quiet]

You could use a flat piece of wood as a jigg something like the pictures shown below.
Place the scales / liners on the board and drill holes through the liner holes half way through the wood.
Place the right size diameter pins through the holes and make sure they are tight in the holes.
You could use this to get a new back spring and blade adjusted to your liking.
I've used this method before and it works well.
You can open and close the knife before you put it together for proper operation.

Hope this helps~

JW

[Elvis]

If you're replacing both the blade and the backspring, I'm guessing that original parts aren't available so you need to modify some to fit. Am I close? I'd recommend using the broken parts as a template to grind the new ones into the correct shape for your knife. If you were building one from scratch, then you'd need all those math problems, a very sensetive instrument called a "rise and fall indicator" and would have probably have had it all figured out on paper before you started. For a repair, all the hard work has already been done and all you would need to do is copy the old parts. "Dry fit" the parts and adjust as needed before reassembly. I type faster than I think, so if something doesn't make sense just ask and we'll try to help.

[just bob]

I have been trying to pull pcs out of boxes and put knives together. Even if you're going with Barlow to Barlow there isn't much chance you are going to find a used back spring that will work in a random knife. Even if they are just a hair off it changes the dynamics of the knife. I was just wondering if there was an easy way to do this? If you are making a knife from scratch do you trace parts of an old knife to determine blade and back spring specs? If you're not tracing parts how do you lay an original knife out you want to make? Also it occured to me on the process shown on here that when you have a knife with no snap and and you take it apart to tig weld the worn spot on the back spring and then machine it back to spec. Why not just grind or file the hangnail from the blade and use the old back spring as a template and create a new one that is a few thousands thicker in the area where the wear was. Wouldn't that serve the same purpose as welding the old back spring? If you did this what would be the formula you would use to determine snap as the blade would be slightly shorter and the backspring slightly thicker? Is it just trial and error? For many that don't know how to weld or have a welder this process might work. I'm going to try it the next time I run into this problem. Thanks for the help on this subject. I'm just trying to learn how things work.

[Elvis]

Why not just grind or file the hangnail from the blade and use the old back spring as a template and create a new one that is a few thousands thicker in the area where the wear was. Wouldn't that serve the same purpose as welding the old back spring?

Doing that would also affect the way the blade lays in the open position (it wouldn't fully open due to the extra thickness of the spring). In short, there's only one correct formula for each knife and the maker figured it out before production began. To try to bypass the correct way a slipjoint goes together is only going to result in something that doesn't work right. And even though this TIG thing might have been my idea, I don't own a TIG welder either. I just found a local welding shop with a talented welder and reasonable prices.