How necessary are steel framelock inserts?

[marthinus]

Mike was familiar with the old locking liner design patented

by Watson & Chadwick in 1906 for Cattaraugus. Used first on

traditional folding hunters, this mechanism became standard on

electricians' pocketknives, and was also used on Cub Scout

knives. In this design, the liner projects above the handle, and

it is split lengthwise, alongside the pivot pin. The side of its

narrow tip engages the front edge of the tang when the locked

blade is open.

Mike noted that only a thin extension of the liner could be

used as the lock in the Watson & Chadwick design. This was

because most of the liner had to engage the pivot pin, in order

to hold the knife together against the tension of the backspring.

The result is that this type of lock is inherently weak.

Mike went back to first principles. He realized that if

spring tension and lock-up could be provided by a liner alone, he

would be able to dispense with the backspring entirely. With the

back spring gone, he could then have the end of the liner cut-out

engage the bottom end of the tang, making for a much stronger and

more positive lock. Indeed it would be nearly as strong as the

old Marble's Safety folder (patented in 1902), while dispensing

with that knife's long, awkward, and fragile fold-up extension

guard (the folded guard serves as that knife's lock when the

blade is opened).



STRONG AND SECURE

As it worked out, Mike had not anticipated just how strong

his new lock would be. About 1984 I helped to run side-by-side

destruction tests of all the types of locking folders available

at that time. Each test involved securing the handle of the knife

without blocking the movement of its blade or spring; then

sliding a one-foot pipe over the open blade (which was oriented

edge downward), to serve as a lever-arm; and finally hanging

weights from the free end of the pipe until the lock failed.

Name-brand conventional factory lockbacks failed at between

5 and 7 foot pounds (except for one that failed with just the

weight of the pipe). A Paul button-lock knife proved to be more

than twice as strong as the best of the conventional lockbacks.

But a Walker Linerlock was nearly four times as strong as the

lockbacks. What's more, when Walker's Locker did finally fail, it

failed in the open position. Instead of closing suddenly upon

failure, as all the other knives did, it seized up and became a

"fixed" blade.



SELF-ADJUSTMENT

This strength turned out to be a fringe benefit of Walker's

self-adjusting design. He based this design upon the simplest of

all mechanisms, the inclined plane, or wedge. The end of the tang

is slightly beveled. The end of the liner is not (although it can

be, as long as the angles do not match). Both parts must be hard.

When the blade is opened all the way, the liner passes the inner

edge of the tang, but it is stopped before it passes the outer

edge. The liner's leading edge bears on the beveled end of the

 

[marthinus]

tang. If the pivot joint loosens over time, the point of

engagement of the lock-up moves further along the bevel, so it

continues to lock up tight.

In the destruction test, when we applied an extreme load to

the blade of Walker's Linerlock, the free end of the locking

liner moved all the way past the end of the tang, and wedged

itself between the blade and the fixed liner. Mike was later able

to disassemble and repair this test knife, and today it is

(almost) as good as new.

In his first Linerlocks (he was not calling them this yet),

Walker made the liners out of spring-tempered 440-C blade steel

(he did, and still does, his own heat treating). The lock-ups

were not yet the full width of the tang -- Michael changed this

after the destruction tests, to make his knives even stronger.

The thick 440-C liners of those early versions applied so

much spring pressure to the blades that no other mechanism was

required to retain the blades in the closed position. But when

Mike began to experiment with lighter gauge liners, he realized

that a separate element would be needed to perform this function,

which is performed by the backspring in conventional knives. In

1984 Mike began to incorporate a ball detent in the frames of his

Linerlocks, allowing the liner to be dedicated totally to lock-up

in the open position, while the ball detent held the folded blade

closed.



TITANIUM

These new lighter gauge liners were made out of titanium

alloy. Titanium has many features that make it especially

suitable for this application.

- Titanium has a high strength to weight ratio.

- Titanium has superb spring retention qualities, without the

necessity of any heat treatment. A titanium spring will recover

from a severe load that would permanently deform a steel spring

of the same cross-section.

- Titanium galls to other metals -- it seizes to them, rather than

slipping past them, when they are rubbed together under tension.

This makes titanium useless for moving parts, but ideal for parts

that are meant to seize, such as the end of a liner engaging the

end of the tang of a folding knife blade.

- Titanium can be electrolytically toned to a wide range of

attractive colors. Michael and Patricia Walker pioneered the

application of this technique to knives. In fact Patricia Walker

was the first artist to engrave and anodize titanium, both on her

husband's knives, and on her own jewelry and artwork.

 

[marthinus]

ADVANTAGES AND LIMITATIONS

Walker's Linerlock mechanism is flexible and forgiving in

many ways. In the 1980s Mike would go to shows with a box full of

unfinished blades that he had ground freehand in all sorts of

shapes. Customers would pick out ones they liked, and Mike would

then make knives around these blades, without any need for the

precise patterns that burden the makers of conventional lockbacks

and slipjoints.

However, one aspect of the Linerlock is not forgiving at

all. This is the bevel at the end of the tang, on which the end

of the locking liner bears. If this angle is too acute, the liner

will slip and the lock will fail. If the angle is too obtuse, the

liner will stick, and the blade will be difficult or impossible

to close.

Mike emphasizes that there is no single correct angle for

this bevel, as some writers have mistakenly claimed. Rather it

must be determined for each knife. The optimal angle is a

function of the blade and liner materials, of the spring tension

of the liner, and most important of all of the overall length of

the knife. The free end of the liner moves in an arc of a circle,

and the length of the knife determines the radius of this circle.



LINERLOCKS TODAY

Mike Walker rarely makes Linerlocks any more. He has

licensed the name, and various aspects of the mechanism

(including the patented safety latches recently developed jointly

by Walker and Ron Lake), to a few other makers and manufacturers.

On his own current knives he uses some of the dozens of other

locking mechanisms that he has invented over the years.

Mike is flattered that so many makers and manufacturers use

his invention, though he is disappointed that most of them fail

to grasp all the subtleties of the Linerlock mechanism. Because

of this, most of their knives lack the strength and smoothness of

Walker's own.

And Mike is angry at certain pompous Johnny-come-lately

makers who attempt to claim credit for his inventions and his

designs. One shameless maker is today receiving royalties for a

design that Walker created two years before that particular maker

assembled his first knife. But Mike never patented his original

mechanism or his early designs, so this sort of copying is now

water over the dam.

However Walker's trademark rights are another story. Mike

lets his lawyers deal with any makers or manufacturers who have

the temerity to use his "Linerlock" trademark without his formal

written permission.

*** END ***

 

[marthinus]

I see a lot of knives are starting to promote steel lock face inserts or carbidized lock faces to supposedly prevent your titanium lock from wearing away from meeting the steel of the blade.

Is this really a concern?

How long would a non protected titanium lock face last against steel?

Am I at risk of ruining my $1000 flipper that does not have a protected lock face by flipping it repeatedly?

Thanks!

If your knife is built right you won't have to worry about it. The lock will break in and shouldn't wear.

Some good work was done here to showcase the influence of lockbar cutout placement, however, it should be noted many knife makers etc have discussed this with engineers and in a knife the difference is negligible. If we were building massive structures then the case would be very different.

Hey guys,

i played around with Solid works to bring some numbers into the discussion weather the cutout inside the frame or outside the frame is stronger and to which degree.
The frame is titanium al6v4. The cutout is 7 mm long and 14 mm wide with 1,4 mm remaining material. The force applied ist 100 N. (SI units ftw )
As you can see is the stress (force/area) with the cutout on the inside two times higher compared to the cutout on the ouside. But even with this great amount of force applied is the stress very low so it is completly irrelevant in terms of construction.
"Streckgrenze" in the bottom right means yield strength which is the stress level above the material deforms non elastic.

The cutout inside:

the cutout on the ouside:

regards, Moritz

 

[marthinus]

Ok. I am done for now.

 

[Comeuppance]

... Probably should have just posted a link to an article, or something...

 

[marthinus]

... Probably should have just posted a link to an article, or something...

Who clicks on links these days?

 

[Jens Schuetz]

If wear is the issue to be fixed a steel insert isnt great, because the blade will now wear as much as the insert. Both are steel.
If the insert is cheaply replaceable but the blade not as much then a softer material for the insert would be best.
Could even be a titanium insert if you ask me.

 

[bodog]

What's funny is that Mike Walker, the dude who put liner locks on the map, actually wanted titanium on steel exactly because it galled. It's more how the lockface and tang are ground that are much more important.

 

[Tyronethepro]

Ill put it this way, I have a boker plus Dark Hollow with a TI scale. 5mm thick blade, 5mm thick scale. EDC'd since February this year, thousands of openings. less than 5% movement and now holding steady. Its Unnecessary.

 

[gopeder111]

I have an older ZT0301 with a pure Ti lock bar. Were the lock bar faces ever treated in any way?

 

[Scurvy092]

What's funny is that Mike Walker, the dude who put liner locks on the map, actually wanted titanium on steel exactly because it galled. It's more how the lockface and tang are ground that are much more important.

RJ Martin is the same way.