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BLADE STEEL
The blade
of course is the heart of the knife. If the steel isn't right
for the intended use then everything else is lost. Knife steel
selection is a process of trade offs just like everything else
in life. Hatchets and chisels are made from low alloy steels
because toughness is the over riding consideration. Taps, dies,
drill bits and bearings are made from tool steel. These steels
are designed to form and cut other metals. Most custom knife
blades are selected from this category. The challenge is to
select the steel that has the right balance of toughness and
wear resistance and to grind and heat treat it so that the full
potential is met. As new steels are introduced I have
discontinued the use of some of my old favorites (ATS 34, 440-C
420HC). My current production is made up of these seven tool and
die steel grades: 154CM, CPM 154, CPM S90V,CPM S30V,CPM 10V, CPM
S110V, CPM M4
I use more
CPM 154 for fillet knives than any other steel. It is very stain
resistant, has very good edge holding, and ductility. The
majority of my hunting knives the last couple of years have been
made with CPM S90V, CPM 154, CPM S-30V or CPM 10V. I use CPM 154
and CPM S-30V for kitchen knives.
The CPM
steels, (Crucible Particle Metallurgy) makeup the largest
percentage of my production. All of the CPM steels have a high
percentage of very hard; very fine carbide particles in the
steel matrix. CPM S90V was introduced in 1997 as an upgrade for
CPM S60V. It has a higher attainable hardness for improved wear
resistance. I worked in conjunction with Crucible Materials to
pioneer the use of CPM S90V for knife blades. I remain one of
the few makers currently offering it because very few are set up
to heat treat this grade. I built a high temperature, precisely
controlled furnace and developed the techniques required for
consistent results. I heat treat CPM S90V to a finish hardness
of (RC 59-61). CPM S90V is still a very good choice for the
ultimate hunting blade but this year (2009), Crucible introduced
an up date for CPM S-90V. The new one is CPM S110V. In addition
to the 10% Vanadium in S-90V, Cobalt, Moly and Niobium have been
added. All these alloys combine to form a complex carbide that
provides excellent wear resistance. Crucible also claims better
corrosion resistance than S90V. This grade still requires the
same attention to heat-treating as S-90V, but the attainable
hardness is much higher. My initial work with CPM S110V, and
subsequent field testing has shown that a Rockwell hardness
range of 62 to 64 provides a good balance of hardness and edge
strength. CPM S110V is currently in short supply since only one
heat of this grade was made initially and it is all gone at this
time. I have enough to last a while but in order to conserve it
I will limit blade types to hidden tang and partial tang
designs.
I have
been working with CPM 154 now for a couple of years. This is
basically the same chemistry as 154 CM and ATS 34 but with a CPM
structure. My experience with it has been very positive. It has
a higher attainable hardness than the original 154 CM grade and
the CPM structure makes for better impact toughness. I still use
154 CM and CPM S-30V for fillet knives and some kitchen knives
but anticipate as time goes on that CPM 154 will replace all
other steels for this application.
CPM 10V
has about the same alloy content as CPM S-90V with the exception
of Chromium. Five percent Chromium is not enough to make it
stain resistant. This however allows a higher attainable
hardness (RC 63-64) with the resultant further increase in wear
resistance and edge holding. CPM 10V has been the edge holding
standard for me ever since I first tried it 15 plus years ago. I
currently offer this steel but only for users who ask for it
specifically and understand the trade offs associated with its
use.
Crucible
made a heat of CPM 125V a few years ago and I purchased enough
to make about 20 knife blades. To date I have only made a few
hunters for test blades. Performance was excellent but due to
fabrication difficulties, I have pretty much dropped this one.
It looks like at this point that CPM S-110V has all the great
potential qualities that CPM S-125V did. It is difficult to
grind and finish but is well worth the effort. My cutting tests
on Manila rope show a
very high wear resistance. It is in the same category as 10V for
edge holding and is stainless as a bonus. I can offer this steel
only at a premium price due to the workability problems and
limited availability of the material.
This year
(2010) I obtained some CPM M4. Preliminary impressions are very
good. It can be used up to RC 64 with reasonable toughness. It
takes a nice polish and seems to get very sharp with minimum
effort. Corrosion resistance is low compared to stainless steels
like CPM S110V and it will require attention to keep it from
pitting and rusting in wet environments. I hope to field test it
this year and will then have a better feel for it’s overall
performance.
Please
refer to the ARTICLES section for more information on these
steels.
HANDLE Materials
I usually
recommend one of the three following materials for a working knife
handle: They are Micarta, Stabilized Wood and Desert Ironwood.
Micarta is an electrical insulating material made from layers
of linen cloth or paper laminated together under heat and pressure.
It has high strength and is sometimes referred to as the steel
of the plastics industry. Stabilized Wood is similar to Micarta
in that it is injected with resin under vacuum and then cured
under pressure. The result is the feel and look of natural wood
but the stability of a plastic. Desert Ironwood is a material
made by nature for knife handles. It is very dense and oily, almost
waxy, very dark brown with gold streaks running through it. It
is becoming a rare hardwood and comes from the Sonoran Desert
in Arizona and Mexico. It is the most stable of all hardwoods
and is well suited to the extremes of salt water and the high
mountain range environments. Stabilized Maple Burl, or Fiddle
Back Maple can be dyed many colors. I like to combine the stabilized
woods with desert ironwood in a multi piece handle. Various spacers
can be added for contrast. The result is a striking effect that
is durable and has the appeal of a natural material. Animal materials
like Stag, Ivory, and Ossic make beautiful handles but should
be considered only if the user is prepared to give the knife extra
special care.
SHEATH
A good
sheath is required for a high quality knife. It provides
protection against damage to the knife and is essential for
safety. In the past, I furnished a heavy duty leather sheath
with each knife. Leather is traditional for a custom knife but
it does have some disadvantages. It can absorb moisture,
accidentally become contaminated and cause corrosion if the
knife is left in the sheath for a few days. This is especially
prevalent in a salt-water environment with fillet knifes. This
year (2009) I made the commitment to tool up to make “Kydex”
sheaths. Kydex is a thermo plastic that can be heated and molded
to the knife. It is impervious to water, the interior can be
rinsed out with soap and water and it forms a very stiff
lightweight substantial sheath. A very sharp knife blade placed
in a leather sheath incorrectly can come right out the side. I
have done this myself with a fillet knife when the sheath was
bent over to one side and I did not notice it. This is not
possible with Kydex due to the hardness of the material. At the
risk of contributing to more plastic in an already plastic world
and appearing to be too “tactical”, I will now be providing a
Kydex sheath as a standard with each knife. It has also been
traditional in the past to provide a belt loop on a knife
sheath. I am drifting away from this requirement based on my own
hunting experiences and from paying attention to what others are
doing. Most fixed blade hunting knives now go in daypacks. A
knife and sheath hanging on a belt is just in the way. The knife
can be damaged or lost in a fall and the handle pokes you in the
ribs every time you bend over or sit down. My advice is carry a
good low cost, high quality (like Spyderco) folder in your
pocket for easy access. keep the higher cost custom knife in a
back pack where it is protected and safe until it is needed.
HEAT TREATING
If the blade
steel is the heart of a knife then the heat treating is the soul.
The best obtainable tool steel in the world will make the worst
very expensive custom knife if the heat treating is not right.
I decided years ago that to be able to control the quality of
my knives I had to do my own heat treating. The high alloy steels
mentioned above can be tricky to heat treat and require good equipment
that is capable of repeatability. Doing my own heat treating was
a big commitment but I'm glad I made the effort and investment
in equipment. I can now precisely control the hardness of each
blade. They are all individually Rockwell hardness tested through
each step of the process. Final adjustments along the way can
be made to arrive at the final hardness desired and the confidence
that they are exactly right for the intended use. I do an ultra
subzero secondary quench in liquid nitrogen to insure complete
conversion to the Martensite phase of the steel. This also insures
stability and toughness for the life of the blade. The quenching
is followed by multiple tempers to insure the best balance between
toughness and hardness.
EDGE GEOMETRY
Many knives are constructed with a thick section at the cutting edge because they have to be built for the hands of an inexperienced user. This makes them somewhat clumsy and hard to sharpen. I elect to trust the user to exercise enough common sense to not abuse the blade. I can therefore grind to a very thin edge. Fillet knives are finished to about 0.010 inch and hunters about 0.010 to 0.015 inch. This allows for very easy sharpening because only a small amount of metal needs to be removed to renew the cutting edge. In fact they will almost cut before they are sharpened. This thin section does however require some care during use. It will hold up very well when used for filleting fish, field dressing and skinning, and normal kitchen and butcher work but is not intended for chopping or prying around bones. A saw or cleaver is best suited for this type of work, and they are much less expensive than a custom knife.
SHARPENING
This is tough to do right with out a lot of practice. I have been frustrated many times in the past trying to get that final shaving edge by making one last stroke on the stone only to lose it all and have to start all over again. I was determined to figure out a method for fool proof sharpening. It starts with the blade itself. As mentioned above if you take a close look at most knives you will find a very thick edge section. It is strong but very hard to sharpen. The ideal edge angle of fifteen to twenty degrees can only be obtained by removing a large amount of material. This is hard work takes time and is almost impossible to do with any precision. A blade steel with good toughness can be ground relatively thin and still be durable. A thin tough edge is only half the solution. The other half is the sharpening stone. In my experience the best sharpening media is Silicon Carbide. Norton’s name for this is “Crystalon”. This sharpening stone is available from them in different configurations with the Crystalon/India combination stone the most popular. Silicon Carbide is the grey side of the stone and works best for initial edge forming. Silicon carbide is harder than the carbides found in the high performance tool steels referenced above so the stone cuts clean and leaves a nice aggressive edge. Final second stage polishing for a surgical type edge can be done with the India side (reddish brown, water stones or with a Silicon Carbide dressed leather strop. I guarantee that the combination of the right blade geometry, superior steel, precise heat treating, and a good stone, will eliminate your sharpening frustrations.
See the sharpening heading on this web site for a detailed tutorial on sharpening and for links to Norton and other recommended suppliers.
BALANCE AND
FEEL
I use a light weight tang
construction for most knives and as already mentioned grind the
blades very thin. This makes for a well balanced package. The
balance plus the overall lightness of the knife provides for a
very lively feel. The knife seems to float in the hand and is
very controllable. This contributes to less fatigue when you
have a big box of fish or a large elk to process. The knife
should naturally fit your hand and the shape should contribute
to safe use. This is especially important when things get wet
and slippery. All my fillet knife designs have a flared butt
section to prevent the hand from slipping backward on the
cutting stroke.
DURABILITY
SEAMOUNT knives intended to be used in the field are constructed
from stain resistant steel in the blade and finger guard. I do a
"satin" finish on all my blades. I do not feel that a mirror
finish is desired or necessary on a working blade. On hidden
tang designs the guard to blade joint is held to a few thousands
of an inch and sealed with glass filled epoxy during assembly.
On full and partial tang designs the handle slabs are all 100%
bonded with epoxy for a full seal. This construction allows for
a minimum number of joints and fasteners to leak. The knife will
be very easy to maintain but will not be completely immune to
corrosion. Stainless tool steel will pit and corrode if not
cleaned up after use. I recommend washing with fresh water and
drying and then spraying the entire knife with a non stick
vegetable spray like "Pam" before putting the knife in the
sheath.
A custom knife if taken care of should last a life time. You can
will it to your grand kids when you are gone. Each knife will
have the highest level of craftsmanship and the very best
materials obtainable. I guarantee it for as long as I can make
knives. I will be happy to sharpen it any time for free and
will recondition it at $25 per hour whenever you think it needs
it.
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