THE LINERLOCK -- RIGHT FROM THE SOURCE

  Michael Walker's invention and development of the LinerlockTM

     by Bernard Levine  (c)1997  -  for Knives Illustrated


     The "Linerlock" knife is now so familiar that it is easy to 

forget that both the knife and the name are relatively recent 

inventions. Michael Walker made the first modern Linerlock in 

1980, and he registered the name Linerlock as a trademark in 

1989. Since the mid 1980s, dozens of hand knifemakers and factory 

knife manufacturers have made locking liner type knives inspired 

by Walker's designs, although very few of them fully understand 

either the advantages or the limitations of this mechanism. The 

best way to understand the Linerlock is to look back at how 

Walker developed it. 



THE EARLY DAYS

     Mike Walker began to make knives early in 1980. One of his 

first customers was a collector and dealer in Red River, New 

Mexico, named Don Buchanan. Mike made ten fixed blade knives for 

Buchanan. Don asked Mike for sheaths to go with these knives. 

Mike made those leather scabbards reluctantly, then announced 

that he hated making sheaths. So Don said, "Make folders." 

     Mike did. He made slip joints. He made lockbacks like the 

factory folding hunters then on the market. He made mid-locks 

with mechanisms copied from antique folders. But he was not 

satisfied with any of these. Walker envisioned an improved folder 

that would do away with what he saw as the many limitations of 

conventional lockbacks. 

     First, he would design a knife that the user could open and 

close safely and easily with one hand, without having to change 

one's grip, or rotate the knife in one's hand. 

     Second, his new knife would do away with the sharp "back 

square" of the conventional pocketknife blade. When a 

conventional blade is closed, its back corner sticks out, and can 

snag the user's clothing. In some folders the back square is 

enclosed by extended bolsters, but this can compromise the shape 

of the handle. Mike envisioned changing the basic geometry of the 

folder, in order to eliminate the problem entirely. 

     Third, and most subtle, his knife would be self-adjusting 

for wear. Other innovative folders of this period, notably the 

Paul knife by Paul Poehlmann (patented 1976), were very strong 

and very sleek, but they required careful adjustment of set 

screws to keep their blades from working loose. 



THE LOCKING LINER

     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 

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. 



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 ***