paulkruse@cfl.rr.com writes:

Paul, for us hardness challenged boaters, would you, could you give
us a small table explaining what hardness numbers to look for in
let's say a rigging knife, diving knife, steak knife, a knife that
can open tin-cans and split wood. As I said, I and probably a few
others are "challenged" in this department and would love some
enlightenment. Oh, yes, are there any easy tests that a laymen can
use to approximate the hardness of a given piece of knife steel.
Something like assayers used to use on minerals i.e. "this substance
will scratch that one but not another one etc..."

Looking forward to your reply - George of Scaramouche

paulkruse@cfl.rr.com
At 02:04 PM 3/4/01, you wrote:

Being as how everybody on the list is a "real sailor" and could not
possibly have not read "The Old Man and the Sea" by Hemingway.
You doubtless recall that the old man's knife snapped because it was too
brittle. And that next time he was going to do things differently.

Capt. Mike Maurice
Near Portland Oregon.

I'm not sure how to answer George's question, but I'll give it a try.

The Rockwell scales are used to measure the hardness of metals.  The B
scale is commonly used for soft metals, whereas the C scale is normally
used for hard metals.  Somewhere in my files at work, Ive got conversion
tables by which these numbers can be converted into the other hardness
measuring systems, and also into the strength of the metal.  All this can be
found in any one of a number of basic engineering reference texts, but is of
limited use in this forum.  Suffice it to say that most of your really good
knives like to brag about high levels of hardness, which typically range
between about 58 and 64 on the Rockwell C scale.

The real question is what you plan to do with the knife.  Ive only got a
few hundred hours of salt water diving time.  Most my underwater time has
been deep inside of fresh water caves.  My biggest concern in that
environment is an entanglement in the line cave divers lay in order to find
there way out again.  You really dont need much of a knife to cut line, and
the smaller the better.  You dont want a big knife which itself becomes a
line trap and the source of the entanglement in the first place.  I carried
two knives, in case I lost one or in case I became too entangled to be able
to physically put my hand onto one of them.  One has a blade a little less
than an inch long and is carried on my left arm.  The other has a four inch
blade and is carried on my left shoulder strap.  Both are of extremely hard
CRES metal, and both are kept sharper than any Exacto knife blade you might
buy in the store.  A friend of mine carves intricate statues out of tooth
picks and sells them for several hundred dollars a piece.  He will pick one
or two good Exacto knife blades out of a package of blades, but he tells
me that my knives are sharper than any out of the box blade.  Folks claim
that rope is tough to cut, but Ive never found that to be the case with a
good sharp knife.  These same two knives would be excellent knives to carry
onboard a trawler.

There is a lot to be said about a serrated edge.  That makes it much easier
to cut rope without the trouble and fuss of having to sharpen it the way I
do.  My four inch dive knife used to have a serrated section, but I removed
it in favor of a plain blade.  A serrated edge can be sharpened in the exact
same way you sharpen a plain edge.

As has already been mentioned in this thread, harder is better for all
reasons except one main reason:  A hard blade tends to be more brittle.  It
is possible to have a knife that is both very hard and very tough, but they
are expensive.  For the knives that most of us buy, you will sacrifice a bit
of hardness to gain much toughness.  This is important if you want to use
your knife as a pry bar or screw driver.  When you see the word tempered
in reference to knife metal, that means that the knife was softened a bit
after it was hardened.  Because of these considerations, I dont like to put
extreme importance on the hardness numbers.  They are only one aspect of the
knife procurement decision analysis.

My best general purpose boat knife is a folding Case knife with two blades.
The metal is plain carbon steel.  If you use it enough, then you should not
have any trouble with a carbon steel knife on a boat.  Ive had this one for
about 30 years and have never had a trouble with corrosion on it.  The metal
is very hard at Rc64, so I sharpen the two blades differently.  The large
blade is honed at a steep angle, so that the edge will not chip with rough
use.  The smaller blade is honed at a very shallow angle so that it will
take an extremely sharp edge for fine work.  Both blades have small nicks
and chips in them, but that is not a problem.  They serve to be a sort of
serrated edge and still cut very well.  If I want to test a knife blade for
hardness, I scratch it with this one.  This knife will scratch any knife
blade, even the ones I have made from files and from power hacksaw blades.
What Im looking for is how easily and deeply it will scratch.  If it is a
really soft knife blade, I can scratch and cut the metal as if it were an
aluminum soda can.  You can use a small file for the same purpose, since the
hardness will be about the same as this knife blade.  Over the years, Ive
learned how to estimate the hardness fairly accurately; but that is not
important to the average person.  All you need is a very hard standard and
then judge the other knives on a relative qualitative scale instead of a
quantitative one.

My rigging knife is an expensive one.  It cost more than 60 dollars about
twenty years ago, and I bought it from a reputable discount mail order house
rather than from the local marina.  Even so, it has the softest blade that I
ve ever seen in any knife.  I dont put a very sharp edge on it.  Rather, I
hit it with my coarse stones and leave it at that.  The resulting edge is
the same as a very fine serrated edge that cuts any rope very quickly.  This
is a folding knife that also has a shackle wrench and a marlin spike in it.
I use the spike at work to open up wire rope for an internal inspection.
The knife that a Japanese sushi chef favors is similar, a plain low carbon
soft steel blade sharpened in a similar manner.  Nothing cuts the fish flesh
into thin slices better.

As for whet stones, I normally use only two.  My coarse stone is 1200 grit
and my fine one is 6000 grit.  If I need it sharper than that, Ill use my
grandfathers old razor hone on it, which is about the same as stones
currently being sold as 8000 grit.  Ill strop it on leather if Im planning
to actually shave with it.  In the absence of leather, Ive used my jeans
followed by the palm of my hand.  Any edge that is not immediately put to
use after sharpening is oiled.  I also have one 120 grit stone for shaping
the edge before sharpening it.  Then I have a large assortment of small
stones of various shapes for sharpening surfaces that are not flat.  I
sometimes use them to regenerate a serrated surface that has been worn flat
with too much application to the whet stone.

So you see, there are some applications for soft steel knives, but for the
most part harder is better.  Ive made a number of knives that combine both,
with a .035 thick layer of extremely hard tool steel laminated between
sheets of very soft steel.  These knives sharpen extremely quickly, you just
about cannot break them, and they hold an edge just about forever.  Believe
it or not, stock of this sort is very cheap for a knife maker to buy.  I
wish I could find some stock that has tool steel sandwiched between layers
of CRES instead of soft carbon steel.  That would be the ideal.

Paul Kruse
paulkruse@cfl.rr.com

-----Original Message-----
From: George Geist [mailto:scaramouche@tvo.org]
Sent: Sunday, March 04, 2001 8:49 AM
To: paulkruse@cfl.rr.com
Cc: trawler-world-list@samurai.com
Subject: Re: TWL: RE: Dive knives

paulkruse@cfl.rr.com writes:

Paul, for us hardness challenged boaters, would you, could you give
us a small table explaining what hardness numbers to look for in
let's say a rigging knife, diving knife, steak knife, a knife that
can open tin-cans and split wood. As I said, I and probably a few
others are "challenged" in this department and would love some
enlightenment. Oh, yes, are there any easy tests that a laymen can
use to approximate the hardness of a given piece of knife steel.
Something like assayers used to use on minerals i.e. "this substance
will scratch that one but not another one etc..."

Looking forward to your reply - George of Scaramouche

At 02:04 PM 3/4/01, Paul Kruse wrote:

After which Capt. Mike Maurice reminded us:
Being as how everybody on the list is a "real sailor" and could not
possibly have not read "The Old Man and the Sea" by Hemingway.
You doubtless recall that the old man's knife snapped because it was too
brittle. And that next time he was going to do things differently.

Paul Kruse now continues that line of thought:
Such things can happen with any knife, but it is much less likely to happen
today with our modern manufacturing controls over the metallurgy.  If you
are willing to pay enough money, you can get a knife that is both hard and
tough.  They have developed a number of very excellent tool steels in the
last several decades, since the time of the Old Man's blacksmith.

I used to have a very excellent Buck knife that was very hard, but not so
tough.  It had a CRES blade.  I'm not sure the alloy, but it held a very
excellent edge.  I'm pretty sure that it was not a fine tool steel, though;
because the knife simply did not cost enough at about 50 dollars in 1977.  I
broke that knife blade many times, each time sending it back for a free
replacement; until I finally lost the knife.

That last paragraph only becomes interesting after reading an article in a
trade journal where a lab tested fine cutting edges from many of the very
expensive manufacturers.  The performance of the tools was evaluated by
tradesmen and craftsmen, and then the metallurgy was evaluated by a
metallurgist.  Then they threw two cheap tools into the mix just for a
control.  One of the really cheap tools was judged good for nothing more
than scraping gum off the side walk.  The other of the cheap controls was a
Buck, which sold for less than ten percent of the average cost of the rest
of the tools tested.  The bottom line is that it really did not matter which
high end tool you bought.  They all performed the same, and their metallurgy
was the same.  What was really amazing is that the Buck performed so well
that for all practical purposes it was the same as an expensive tool for a
small fraction of the cost.  It was so close that the folks running this
test sent their metallurgist to talk to a Buck engineer.

The metallurgist told the Buck engineer that for a very tiny cost, he could
almost match the performance of the expensive tools made from the expensive
tool steel.  This turned out to be something the engineer already knew, but
his response was interesting.  He said that he was making tools that anyone
could afford.  He could make tools practically just as good as the expensive
ones for the same low cost, but his lawyers prevent him.  When you make
tools that anyone can afford, then you have to assume that they will be
abused in more ways than it is possible to imagine.  He therefore has to
soften the tools to make them a little tougher.  Well, I guess he did not
soften them enough to make them tough enough for this old knife-abusing
fool.

Capt. Mike is right, that my original statement is not entirely true.  You
will have to sacrifice a little hardness to gain a lot of toughness
regardless of the alloy used, but if you use some of the more expensive tool
steel alloys, you will start with more hardness than was ever reasonable
before:  And then you will have to sacrifice less hardness to buy your
toughness than blacksmiths of old would ever have thought possible.  You can
end up with a knife that is both harder and tougher than your grandfather's
knife maker ever dreamed about.  I don't buy those knives, though.  They are
too expensive.  The ones in the medium price range are like that Buck that
is almost there, but you just need to be a little careful how you use it.  I
was never able to break that knife without seriously abusing it.  But then
that is what tools are for.  You use them for whatever you need to use them
for, and then you buy new ones on those rare occasions when they break.