Folding Knife Design Problem?

[Akad]

So I've been thinking about making a folding knife. I decided I liked the lock back design, though a liner lock was a close second. I understand how both stay open when in use, and how you close them as well. My question is this:

 

When you close the knife, does it stay closed via friction alone, or is there a mechanism that helps keep it closed that I'm ignorant about? (Although, technically any such mechanism would do so with friction :P )

 

I think with a liner lock the spring presses up against the blade to help keep it closed. At least, that's how it appears to be on my current knife, a liner lock.

 

Obviously I don't want to make a blade, assemble the parts, and then have the knife not stay closed properly (The words dangerous and useless both come to mind). If it's just a matter of making the joint tight enough, that'll be fine.

 

(I searched the forums, but most of the tutorials are for heat treating, etc., I didn't see a ton on design of locking mechanisms. But being a busy, tired student it is possible that I overlooked something. If that is the case, post the link, please and thank you!)

[Rich Hale]

Take a cheap one of each style apart and figure them out,,,,,,

[Stephen Olivo]

Most of the locks, liner and lock backs, that I have taken apart (keep in mind not as many as I like because not everyone wants to borrow me their knives to disassemble and take detailed drawings off of :D) Have a simple flat part of the back rotating portion of the blade that uses friction and a cam action to keep the blade closed (hopefully I explained that well). Though I have seen plenty of complicated folders that have extra mechanisms to hold them closed. These often just wind up being a nuisance in the general use of the knife i.m.o. and make it more complicated to make. One that I have drawings off of has a small indent in the side that the liner lock just barely catches in when closed to help keep it closed. The lock backs just have a flat section that they rest upon adding just a little cam action to the spring as it opens so that you are required to add pressure for it to open. These are just the observations off of the drawings I have sitting in my sketchbook open in front of me. I am also in the process of "trying" to make a lock back folder with pictures along the way (more for my own reference and learning. keep in mind I am really new to knife making) This one will have a flat section for the lever to rest against.....We shall see how well mine works hopefully relatively soon. If it works well it will be a present for the father in law.(fingers crossed).....I hope this helps :D

The flat section is the same way a simple friction folder (like the swiss army knives) stay closed (this is how my first one was made under instruction from Mike Blue and it holds well closed though the transition is a little to rounded between the flat section and the curve allowing less energy to open it then I might want. This also might be from the curve not being far enough from the pivot point. Hopefully someone with more knowledge on the hard part of these knives will chime in to correct me :D)

[Akad]

Ok I think that helps, thank you. Hopefully I'll have some time this weekend to *carefully* disassemble this old lockback I have. It only cost a buck when I bought it, and I quit using it when the clip broke off. For a cheapy knife it locks and stays closed alright so it should be a decent model to go off of.

[Justin Carnecchia]

On a liner lock there is typically a detent ball. So a small ball pressed into the spring that fits into a small divot in the tang. On a lock back the pressure from the spring holds it shut. Neither of these hold the blade very tightly though, thats why you can do things like flippers.

Of the two I would say that the liner lock is much easier to build, at least for a first effort. Thare are also several very good tutorials on the subject, I would read as many as you can find.

Also to consider would be a slipjoint, or a friction folder.

[yesteryearforge]

Research the ( walk and the talk ) of folders

Ive not made a lot of them but when you have the walk and the talk right it makes all the difference in the world in the quality of the knife

[Akad]

Ok, so yesterday I had some down time and drew up the handle and blade, with a cutaway view to show the spring and the locking bar thingy. I cut em out and laid them over and I see how it works. Today I took apart the old one I had and makes tons more sense. I might use the spring from it for the knife I'm gonna start working on. However, this doesn't tell me anything for the future. What sort of material is used for the little rod spring in a lockback knife?

 

I've heard music wire can work as well, and I could probably get some of that pretty easily. Would anyone know about that/recommend it?

 

I mean, if all else fails I could probably keep buying those $1.00 lockbacks and taking them apart for their springs, but that seems a bit wasteful and stupid.

 

Other than the spring, the design for a lockback seems pretty simple to make and effective to keep the blade in place.

[son_of_bluegrass]

I've played with music wire from a hobby store some.  From what I've read it is something like 1080 or 1095, that's how I've heat treated it and it's worked.  It is cheap enough to get some and play with for yourself.

 

ron

[EtownAndrew]

I have used a sliver from an old industrial band saw blade for several lock back knives. I have to harden and blue temper it. I pulled the band saw blade out of the dumpster at work.

[Zanshin]

For a liner lock, as already said, there is a detent micro sphere pressed into the spring/liner at te upper corner usually that "falls" into a little blind hole drilled in the flat face of the blade in closed position. It looks not enough but if done properly it can stop the blade from opening quite well and safely. For the lock back: in closed position it works exactly like a slipjoint, with the head of the spring pressing down the heel of the blade beyond the pivot so that the blade rises inside the handle. Although, I designed, some months ago, a lock in closed position that works perfectly, but it is not simple because you have to do it very last thing on the knife, so if you give just a single file stroke too much you can jeopardize the whole thing.

 

I attached a couple of pics. This is the way I use, I like to reduce the quantity of pieces in my knives. The spring is one piece with the back. In those pics it is oversized, I carefully grind it after HT to reach the strength I desire. This way of making the mechanism allows me to reduce a little the size of the butt of the handle. I put just one pin at the end of the spring to force it upwards. This spring is MA5M (420C) but you can make it in any carbon steel you want. I'd rather use C45 (1045 I think) because it decreases the possibilities of breaking since I usually close my folders with rivets and not with screws.

 

This is just my experience I hope it helps

 

Francesco