Proper Liner-Lock Engagement?

Megalobyte

Megalobyte

Joined
Jun 5, 2002
Messages
2,761
I like liner locks, especially the really thick, heavy duty kind, or even better, frame locks like the thick, bank-vault-like Sebenza lock, but i always wonder about what is the proper proportion of engagement in liner to blade?

You see some knives, many art customs are this way, where the liner is fairly thin, and just barely catches the left hand side of the blade's base, with a lot more room to move to the right, and it seems to work just fine if the geometry is correct, however i often wish the liner would engage the blade more fully, more towards the center of the blade's base, BUT, i do NOT like a liner to go too far to the right, i feel it should still be towards the left side of the base, and i wouldnt want the liner and blade base to be perfectly even/flush with each other either, even if that seems like it would be very strong since it would be the most possible engagement. I guess for me, i like a thick liner that engages fully the left 65-75% of the blade's base, but leaves that last 25-35% on the right hand side. To me, the Sebenza gets it right, more than enough liner to blade engagement, but there is still some base left over on the right. If it goes too far over to the right, i think its actually losing strength, plus it just seems kind of sloppy to me. It also seems as if liners tend to move a bit more towards the right with use.

What do you guys think. Where do you like the liner to be in relation to the blade's base? Pics would be good too to illustrate your opinion if youd care to give one.

Ari
 
Im like you; I build my knives so that the leading edge of the lock travels half way accross the blade tang ( sometimes it goes a bit further). This along with the correct geometry, ensures against any slippage, and provides for a ton of lockup strength. The nice thing is that IF the lock ever wears enough to touch the other liner, it can be peened if the maker knows what he is doing. -- Charles
 
Good question Ari, i have noticed some makers like Ken Onion, Michael Vagnino, Larry Chew and Mike Obenauf (just to name a few i have that are handy) puts a slant on the back of their custom blades where the liner lock goes so it can't move too far over, otherwise if the liner goes all the way over it will loose tension which equals strength. BTW Obenauf's liner lock is almost in the center just slightly to the left where as the others are all on the left side of the blade period, all have good lockup.

Frame locks are way thicker then liner locks and like the Sebenza's are designed to move more then half way over for total strength.

James
 
This is where it all comes down to geometry. The tang of the blade is usually ground to between 5 and 7 degrees. This makes sure that the liner moves over to the same spot everytime. Some makers have a small amount of the liner engage so after time the lock can wear in. I feel that this is not suficient. I have used the same spyderco linerlock for 7 years and it has just finally worn in and needed peening. What most makers have trouble doing is keeping the lock from "biting". The tang of the knife is angled, and if you leave the liner square the edge tends to "Bite" in. The correct way, is to angle the liner lock to the same angle as the tang of the knife. The problem is when you finally get it to not bite, you have filed away too much of the liner and now it goes all the way over! The amount of coverage that is good to use as a standard is: The liner should contact the distance as it's thickness. Meaning that if the liner is .050 thick, the liner should be contacting with .050 of the tang. It should look like there is a straight line on the left side of the blade and liner.
 
If the lock is ground and matched to the tang properly I like it to engage right at the left side of the tang.

If it's not ground properly I don't keep it, just an accident waiting to happen.
 
I grind the lock bevels on all my knives at 7 1/2 degrees, with 2.25" radius, I built a special grinder specifically for this job. I still check each one with proctracter to be sure. The face of the lock is fitted so it has the same angle as the tang ( at least as close as humanly possible with the naked eye ). Just FYI -- Charles
 
IMO the perfect liner lock engagement. Carson M#4.
Locks up like a vault. :) Sounds like a vault closing too.:D
attachment.php
 
Okay, I think the very question doesn't make sense, because by design liner locks are meant to change position over time. It would be very odd if a lock that was purpose-designed to change position, really only had one position that was "perfect". Why design it to change positions then?

The liner is going to wear, period. As it wears, it will move over to the right. At the point that it hits the far scales, there is no more room to wear, so when the liner inevitably wears just a little more, the lockup becomes suspect and blade play gets introduced. At this point, the liner lock is technically worn out, but there are ways to fix it, like introducing a bigger stop pin, which will send the liner back to the left again.

Overall, IMO the answer to the question of "proper proportion of engagement to blade" is, provided the lockup is secure and not susceptible to accidental failure, the entire range of liner-to-the-left to liner-to-the-right is "proper". Obviously, on a new knife, it's desireable to see the liner a bit more to the left, since that gives it lots of room to wear, and a longer lifetime. Beyond that, I have seen liner locks that are susceptible to failure even though the lock is way far to the right, or in the middle, or anywhere else. There is absolutely no particular lockup position that will guarantee you best lock safety. I've seen liner locks with the liners hanging precipitously off the blade tang way to the left, that I couldn't fail no matter what. The challenge of liner locks is getting the geometry right across the entire lockup range, not trying to find one perfect position, because none exists.

Another of many variables here is the tang ramp. The smaller the angle on the ramp, the tighter the lockup (to the point that it could take two hands to unlock) but the more quickly the lock wears. The bigger the angle, the slower the wear, but the more critical the lockup geometry. As usual, there's no clear right answer: just like choice of blade steel and method of heat treatment, it's up to the knifemaker to make the right tradeoffs for his customers. 7 degrees-ish is popular.

Joe

[ edited to change "pivot pin" to "stop pin" (oops!) thanks to cpirtle for pointing that out]
 
Yup, looking at my EKI Mini Commander, which has the slight bevel at the base of the blade where the lock engages, in lockup the left side (looking down on the edge, tip forward) of the liner is exactly flush with the left side of the blade, so that 100% of the linerlock is engaged, but not so far that it leaves any base exposed on the left.

Essentially the same as the Carson folder lockup samhell posted, altho perhaps not quite as pretty...

New knife, of course, I guess eventually it will wear it's way to the right, but the bevel seems to limit that travel.
 
One last note. The liner locks on new knives often have a "break in" period where they move to the right very quickly. So for me, the optimum position of the liner for a brand new knife is hanging very slightly off the left side of the liner. Then I open in 25 times with moderate force, and the liner will quickly move right and engage across its entire face on the left side. But I'm picking nits here, as long as the liner starts off to the left, I'm happy.

Joe
 
Informative post Joe, as usual.

Is there any testing data regarding the number of cycles it takes to wear a Titanium or SS liner matched up with a SS/154CM or ATS34 blade, for example?

I'm looking at the lock on my Commander and wondering how many times I'm going to have to open and close this sucker to wear the lock out, considering the interface is (very lightly)lubricated (FP10) and friction seems pretty low to be wearing the liner at any kind of sustained rate.

It does stick at the far right edge though, so I guess there must be a few molecules shearing off. Seems like it would take a long, long time to shred enough liner off to get it all the way across that tang ramp.
 
Well said Joe.

I think the locks wear based on use more so than the number of times it's opened. A knife used much harder will degrage faster with less openings than a knife only opened and closed.

I have found that the easiest thing to do with a knife who's liner has worn out is to put in a slightly larger stop pin. Of course that depends heavily on the design of the knife but works wonders and can be a DIY project.

Hey Joe, I have seen frame locks that when opened just engage the tang at the "sweet spot" and exhibit no blade play, but if you cut a shoe lace with it the lock bar slide almost all of the way over. Any thoghts on what the cause is? (e.g too much lock tension, loose stop pin etc..)
 
Just to clear things up, you cannot re-locate the liner lock by adding a larger pivot pin. If you make the hole in the blade larger it will still be centered in the same spot. It's just like starting a hole in a piece of steel with a 1/8 drill, then opening it up to 1/2. The center of the hole stays in the same place. You can add a larger stop pin which will keep the blade from opening as far as it origionally did, but then the knife might not look opened and the asthetics will be off.

Cpirtle, to answer your question there are a number of things that can the lock bar to slide almost all of the way over.

First if there is some play in the pivot of the knife, meaning the pivot has worn out (which should not happen) or the hole was not precision reamed to fit the pivot and the hole in the blade is oversize.

Second, the stop pin has some play in it.

Third, the hole in the blade is not round.

Fourth, The lock was undercut when the knife was built and the maker peened over the left side so it would catch. Not much can stick when it is peened over. Any pressure on the blade lets the lock slide over because there is not enough contact.

Just a few thoughts. If a folder is made correctly none of this should happen.
 
Originally posted by striper28
If a folder is made correctly none of this should happen.
Click to expand...

That's the rule of thumb I've been following ;)

(I've seen it several times on brand new custom frame locks)
 
ya, I meant stop pin, not pivot pin. I think I edited my post just before you added your correction ...

BTW, I've seen what cpirtle has seen many times, never quite knew all of what might be responsible. thanks for the explanation! Peening over the lock, that seems downright fraudulent.

Joe
 
The tightness of the pivot on my Buck Strider folder affects the lockup greatly.

When it's set to be pretty tight (but still flickable due to the heavy blade), the lockup after flicking is almost perfect. Pretty much all the way to the left of the tang, full contact. But if I loosen up the pivot (or when it loosens up due to repeated cycling of the lock), flicking the blade out leads to the liner engaging a little past the midline.

Nothing to really worry about, just an observation. I need to get some Loc-Tite.

One question: will the ATS-34 blade or the Ti liners wear out more?
 
Originally posted by AlphalphaPB

One question: will the ATS-34 blade or the Ti liners wear out more?
Click to expand...

It's the liners that will wear. In fact, some makers feel Ti wears too quickly, and have gone with stainless steel liners for that reason.

Joe
 
Thanks for the info. That's what I thought, somehow the Ti doesn't feel as strong. When I'm putting pressure on the liner to close it, it feels weaker than other stainless steel liners, but that could be because of the sheer length of the piece of metal in the B/S.

Then the only advantage is that Ti liners won't rust, so I don't have to worry about taking off scales to clean them.
 
The Carson/Vanguard folder that just came has the same lockup as in the picture samhell showed. Bank vault lockup here also! I also have a Obenauf model 2 that locks up the same and it is also bank vault locked. Another Obenauf model 2 comes over about 1/2 way but is also locked up tight. My JW Smith comes over about 1/3 of the way and.........you guessed it, bank vault tight!
 
You must log in or register to reply here.
Back
Top