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
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
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
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
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
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.