Thin Liners ??

T

The Towcutter

Joined
Jan 16, 2001
Messages
166
I've had the opportunity to view quite a few custom knives this year and I'm seeing a common problem - thin liners and poorly functioning liner locks.

I'm not going to name names, but alot of big names out there, who command pretty high prices, use very thin stock for their liners. I can understand thin liners on a gents knife, but on a tactical knife with robust handles, nothing seems more out of place than a puny liner lock.

All the custom framelocks that I have played with have been great, but most of the liner locks have not. Why is this? Is it just me??
 
Less than .050 liner thickness on a folder with a 3.5" blade or 8" overall length.

My Emerson Production CQC7 has .050 liners. Quite a few knives I've seen have that size or thinner liner on a larger knife.
 
I would agree that .050 or less Ti are too thin for a larger working folder. My normal rule of thumb is .055 for a 3" blade, .060+ for a 3.5", and .065+ for 4" and larger.
The new in house framelock collaboration we are doing has a 3.5" blade and .160 sideplates with an inside relief milled down to .090+.
 
.050 is about as thin as I will go on my fancy folders, and 3" or less blades. Currently anything larger than 3" is a framelock from me, with the lock milled internally to .060-.065.
 
I have always felt that a frame lock is best. Liner locks are usually too thin. I think this is because most makers want to conserve on the width of the handle knowing that it will be in a customers pocket, being too fat with scales and a blade sandwiched between will be too heavy and too think folder for comfortable carry. Anyway, I prefer a frame lock. Two reasons, most are at least as thick as the blade is. This is as it should be, as thick or thicker ! Take CRK, his liners are just a smidgen thicker than his blades. Therefore maximum contact is always kept. It also leave little room for flex in the Ti locking bar unlike some liner locks with thin liners. Next, the fact that you are in better control of how the handle is klocked. You are actually holding the lock shut when using the blade. Less possibility for disengagement. Frame locks are kickass. :D
 
Keep in mind the lock geometry can be more important than the liner thickness. I didn't believe it until recently, either.

Recently I made three "tactical" knives with 3.5-3.8" blades and 0.050", 0.070" and 0.083" liners with TONS of locking pressure (in static position, about 2x across the blade tang), engaged at 50% of the tang, fail a moderate spinewhack as well as a moderate (prob less than 15 lbs, sustained) spine push test. Two were straight cut and one was radiused.

Therefore, they failed, NOT for the following reasons:

1- liner thickness
2- lock static tension
3- lock to tang engagement
4- tang cut type (straight vs. radiused)

The linerlock scares me deeply.

Then again... I don't like 0.050" liners just for the reason that they don't provide as much locking pressure.

-jon
 
That too, I am a fan of the straight pivot area tamg cut. Ya gotta have straight. Like say in Terzuola's book where he shows ypu how. That makes the most sense. Straight Ti liner lock on the straight cut. The have to fit. The andle of the straight cut on the inside or width is crucial too. Lastly, the relief in the locking mechanism is soooo important. I find, not so much in which side. Some people prefer one side to the other. I.E., inside the handle or outside facing the hand. It's the bend that matter there and the amnount of material equal or greater to the blade width. That couple with the leat flex possible in the lock between the blade contact end and the releif end. It ain't as easy as it looks folks, not if ya want it to be a strong, long lasting and safe user.....RDT:D
 
One thing I've noticed on Framelocks is that they are all cut down so you can dis-engage the lock. You can't push a 1/8" framelock lock over unless it is relieved....some I have looked at AND measured are down around .060 to .070...so you don't gain any locking pressure over a liner lock that is .060 to .070. The only advantage of the framelock is in use your finger is wrapped around the lock bar which pretty much keeps pressure on the lock and tang constant.
I've noticed on some liner locks that the inside roll of your finger actually disengages the lock slightly on a poorly designed folder when you grip tightly.
Now, .060 Ti is .060 Ti regardless of how wide the lock face is at the tang. If you applied pressure to the lock until it buckled, it would buckle at the same place every time....the thinest cross section.
On the other hand how wide the lock is at the bending radius has a great deal to do with lock strength. An .060 x say 1/4" lock bar is not going to be any stronger than an .050 x 7/16" lock bar due to the greater cross section of the the .050 lock. I haven't set down and done the area calculations, but I can and that information along with the Modulus of Elasticity and Strength of Material data..that is the external forces, tension, compression, bending, shearing and torsional stresses within the lock bar,it would be possible to graphiclly display which lock is, in reality, stronger.
To work the Factor of Saftey calcs requires 4 factors.
1. The ratio of the strength of the material to the elastic limit.
2. Is the character of the stress within the material..like a dead load or a varying load.
3. The manner with which the load is applied. Gradually or an impact load.
4. The last factor is called the factor of ignorance. The other 3 factors apply to known conditions, but this factor, my favorite one btw, provides for the unknown and is variable.
So my best advice is be careful and don't get your ass caught in that last factor. Good evening. lazza
 
Originally posted by dson
4. The last factor is called the factor of ignorance. The other 3 factors apply to known conditions, but this factor, my favorite one btw, provides for the unknown and is variable. So my best advice is be careful and don't get your ass caught in that last factor. Good evening. lazza
Click to expand...

Larry, ya did good.:D

A.T.

My next show is the SouthEastern Show
in Winston-Salem, NC, September 6th and 7th.
Please come by and say hello.
"Don't you buy no ugly knife"
http://www.customknives.com/
 
Hey, what happened to everybody???? I thought we were just getting started!!! Must be the summer slump....:p
A.T. I knew you were lurking out there......;)
 
Larry,
You hit it on the head! I could not have said it better.

Coefficient of friction is what causes all locks (no matter what kind) to fail. The job of a knifemaker who is utilizing the liner lock is to know how to lessen this coefficient of friction in order to make it work. But it is not a simple answer. You have your lock and you have your blade, the thickness of your liner has nothing to do with your lock-up. I can make a .050 liner outperform a .070 liner all by manipulating the length and width. Titanium flexes the same no matter in what size; what makes one more rigid than the other is the length, thickness and width. If you want to know the real secret behind a liner lock, examine the blade. You guys are looking at the wrong thing.
I hope this helps out.
Allen:p
 
Lots of good stuff here. I believe the characteristic of thin liner failure is known as column bending, and, ultimately, column buckling. The reason a relieved framelock will sustain more load than a constant thickness liner (of the same thickness as the relieved framelock) is that the framelock is much more rigid in the direction of the load, since it won't buckle as easily. Once the liner buckles, it becomes effectively shorter, and alters the lock engagement geometry. This only worsens the condition, and, failure occurs soon after.
Most linerlocks have the liner bent in an arch, which makes it that much easier to bow. Most framelocks have a distinct bent at the relieved area, leaving the full thickness portion straight. This configuration is far more difficult to bow, since there is no sideways component to the load traveling through it. Not to mention the fact that the liner is thicker.

Columns react much better to loads applied along their length than to sideways loads!

Now, I'd like to hear more about Allen's comment on the ideal tang geometry/finish.
 
Hi R.J., how are you? I'll try to keep this short.

#1 - You want the locking surface on your blade (let's call it the tang) to be perpendicular to your pivot.

#2 - You want to get the locking contact as low as possible to the pivot.

These will help out in the lock strength in the sense of leverage.

Ideally, having a zero angle on your tang is the strongest. But that would not work for us because we would get up and down play. If you use a 1 to 5 degree angle, the lock-up is very very strong. You are almost garanteed no slipage, no matter what type of liner thickness you use. The problem with this is that you are dabbling into the angles of locking tapers, so your lock is going to jam behind your blade.

The surface finish on the blade and on the face of the lock have a lot to do with the coefficient of friction. The finer the finish, the lower the coefficient. For example if you use an 8 degree on your tang and you mirror finish that surface, the lock might have a hard time staying in place. But if the surface was finished to a 400 grit, you might not have any problems of it slipping. This is only an example!

This is the formula that I use: 7 degrees, mirror finish tang, straight cut (not radiused), .050 liners, 3/8" high and 2 1/4" long. There are only 2 bends on the liner: one in the center very slight to keep the liner flat in the closed position and a second bend on the very tail end of the lock. If you removed the blade, the lock would barely touch the other liner. That tells you how much I bend my lock.
I do not get a bad jamming or sticking problem and the knives usually pass the spine whack test with flying colors on the first attempt.

Now the last batch of knives I made, I used 6 degrees. One out of 3 knives had an unacceptable sticking problem. I used the above formula except for the degree that I changed. But every knife locked-up and passed the spine whack test on the first shot.

Next time around I am going to try 6.5 degrees. But you have to remember that a lot of things happen when you drop from an 8 (a lot of makers use that angle) to a 7 degree or to a 6 and so on... Investing in a good vernier protractor will tell you the exact angle you have set for your blade.

One last thing... I usually try to set my lock a little bit past the thickness of the lock when it engages the blade. If the liner is .050, the engagement point would be about .060 into the blade. The further in you go with your lock, the harder it is to disengage the lock. This is just about angles and leverages. A lot of people believe incorrectly that the liner should be on line with the side of the blade.

Sorry to be so long winded but it is hard to explain in a couple of sentences.

Allen
 
Allen: I'm well, thanks. Your points pretty much mirror my experiences, especially about the criticality of consistency, and variability of the final lock-up when things change even a little bit.

And, some of the rules change considerably when the liner thickness increases.

Stay Sharp,

RJ Martin
 
Allen & RJ,
Good posts.
I also feel the thickness of the washer/bushing/whateverit'scalled makes a difference in the angle.
In a framelock I prefer to go more toward 9° to keep the lockbar from going too far into the blade. I also use a 1° relief angle on the tang of the blade.
 
I've dropped down to 7° to 7-1/2°. Since I machine my lock bar faces I also have a 1°angle away from the blade tang from .100 about the lockbar/tang contact area to avoid any and all contact in the mid tang area of the blade...ensures no rocking that can come for even a slight amount of contact there. That's been my experience.
I agree with Kit about the affect different washer thickness's have on the lock angle. I've found using the Chew Voodoo requires setting them to a depth that will leave the exact thickness above the inside of the liners as the washers I use on other models. If I change it I have experienced lock up problems. Especially lock sticking.

For the record, the Factor of Ignorance is indeed a legitimate engineering term(straight from the Material Strength Handbook).
It was not used to imply anyone involved in this disscussion was a moron. Just to point out the unknowns as the last few exchanges are clear examples of the "variables" we work with. Material thickness and strength are considerations not to be taken lightly, but if poor engineering and execution of the design intent occur the former considerations hardly matter. That's my current conclusion anyway.ld
 
Hmm.

Now I'm confused.

Why do makers disfavour the radiused tang?

I always thought that a straight-cut tang would be more prone to having the lock face slipping off the tang due to friction failure.

I'd thought that a radiused tang, with its perpendicular terminal portion (where the radiused tang goes "flat"), any force applied to the spine would cause the lock to slip, but eventually reach the "flat" portion and be entirely normal to the tang/face mating surface. This, in effect, would create a "broken fixed blade", but where there was no shearing component and the force was entirely tangential to the two surfaces.

This is compared to the straight-cut tang, where the force -always- has some shear component and relies on friction and lock tension to hold the lock bar in place. Once the lock slips, it keeps slipping, as compared to the radiused setup, where the lock can slip until the force is tangential, whereupon there is no shearing component.

?

Thanks for any clarification. :)

-Jon
 
What are the advantages of a thick liner then? If thickness doesn't really matter, why go thick at all? Would it be a thick liner gives you more material to prolong lock life?

To be honest, I think thin liners on a big folder look out of place. They may function fine, but they look chintzy, like a cost saving measure. I know this is often not the case, but it appears that way.
 
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