Folder pivots & some 6/4 Ti questions

Chiro75

Chiro75

Joined
Feb 4, 1999
Messages
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Question on folder pivots (yes, I know, my desire to do a folder rears its ugly head every few months)... how tight of a fit should there be between the blade and the pivot, and the pivot and the scales/liner materials? Every folder I own has just a plain pivot with screws holding everything together (as opposed to bearings and such). So, I feel like there must be a little play between the hole in the blade and the pivot pin, otherwise if the fit is too tight it would rotate the whole pivot assembly back and forth, no? So on a 3/16" outer diameter pivot pin, I have the recommended drill bit that is slightly undersized and the reamer, but is that going to make too tight of a fit?

I was talking with a maker at the knife show a couple weekends ago and he had this mega huge tactical folder that he makes as something diofferent now and then. He said there is some slop inm the works and when it all fits together the slop is gone. The knife felt perfect to me, no slop, perfect lockup, etc.

Also, I'm still sold on a framelock with a Ti frame. Is it even possible to use 6Al/4V of that thickness and cut it with dremel cut off wheels and such? Finally, does anything need to be done to 6/4 to harden it for framelocks?
 
I don't know the answers to any of your questions, but I've spent a while wondering about the same things and here are some things I've found out and some of my thoughts:

- Ideally, there is as little play between the blade and pivot as possible. A perfect slip fit. I've seen a lot of production folders with pivots that key into stamped or laser cut irregular holes to keep from turning. My Sebenza, on the other hand, has an oval-head screw on one side, a pivot nut with an oval head on the other side, and a steel sleeve that fits (perfectly) between the hole in the blade and the pivot. The friction between the head of the pivot and its countersunk hole is enough to keep it from turning. There are big thrust bearings (aka bronze washers) between the blade and the scales, and everything is greased. There is really no play in any direction. It all just fits together. At work, we use undersize reamers for press-fit holes when things aren't going to move. You might have better luck with an on-size reamer. If it's still too tight then (AFTER you heat treat the blade), try and find some way to hone the inside of the hole.

- On the other hand, with the three-point contact involved in a framelock, some of the slop may be taken up when you lock the knife as the blade levers against the stop pin.

- As far as I understand it, Grade 5 Ti (6Al4V) should work with cutoff wheels without too much trouble (just don't slip and mess up your expensive piece of metal). You can even file it when you're doing the final adjustments to the lockup.

- Yes, Ti can and should be heat-treated in a frame lock. I think that this will help stabilize the spring. I know that it makes the end of the lockbar more wear-resistant, which is absolutely beneficial. Also, I don't think Ti goes above 50 HRC or so, so you can continue adjusting the fit of the lock after HT. I think Ti is age-hardening but I don't have specs handy.

-Allin
 
Hmmm. So, how does one HT the framelock in a basement shop? I've cut the thin 6/4 with cutoff wheels, but it really chews them up. Maybe I'll buy a waterjet cutter! :D
 
Yes, a dremel will cut 6AL/4V.

No, it doesn't need any heat treat.

The pivot should be a close slip fit.
 
Sounds like the slop on the mega tactical folder was taken up when it was opened and the lock pressure got rid of it-not the way to do it. I test a knife by opening it halfway and then pulling and pushing on the blade to see if there is any slop. There shound not be. I drill .010 undersize and then after heat treat ream to size with a carbide reamer. I then mirrior polish my pivot and there is not slop and it is smooth opening.
 
Thanks Striper28. FWIW, one man's slop could be another man's precision fit, so it's tough to say. This guy usually builds really sweet autos and does a crazy tactical monster for fun a few times a year. I didn't feel any play at all at any point in the movement of the knife, so I have a feeling when I asked him if the pivot should be a "tight" fit or have a little "slop" by slop he probably meant a slip fit like you guys are talking about...
 
A close slip fit is a good way to put it. Let say from .0002 - .0005 over the pivot barrel size. That will work fine. If you go much over that you will start having lock and detent problems and other issues with the knife.
 
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