Edge work on a Marine Raider bowie from Ontario

[Cliff Stamp]

Some time ago Rusty loaned me a few blades from Ontario, I thought I had
sent them back to him but they turned up last week when I was cleaning up my
closet, yes I am that organized. In any case I figured I would clean them up
before I sent them back to him and while I was at it put decent working
bevels on the blades, as NIB the cutting ability is not anywhere near where
it should be for a decent working knife. It struck me then that this would
serve as a useful way to showcase the difference in performance just
changing the edge bevel can make, and while I knew what to expect with
normal cutting I had not done enough work chopping to make a solid estimate
so I was curious myself about quantification.

I started off with the Marine Raider Bowie. It is a solid knife, one of the
few Ontario blades I have seen without gross manufacturing flaws. This is a
big chopping class knife with a 10" blade of 1095 carbon steel. It is
decently heavy at 600 g with a blade heavy balance (2.25" in front of center
of index finger), so it has quite a solid heft in hand. All of this
indicates that it should chop fairly well. However the primary grind is
sabre-flat and fairly obtuse at about 7 degrees. The edge bevel is even
worse, about 20 degrees near the choil and getting more obtuse towards the
tip where it maxes out at about 25 degrees. From memory I recall actually
thinning this somewhat when I last sharpened it so it was probably a few
degrees higher NIB.

Getting past the numbers how does it actually chop? I spent some time
cutting up small wood (2.5-3.5") with it and the Wildlife Hatchet from
Gransfors Bruks. Right from the start it was obvious that the bowie was not
in the same class as the hatchet, it could not come close to matching the
penetration. The median performance through 30 cuts (364 chops) put the
bowie at a rank of 63 +/- 3, with the Bruks hatchet at 100. Thus the bowie
is far behind and it will readily take a performance loss on large wood and
thus fall further behind because it will not have the penetration necessary
to open up the wood. Some few test runs on larger wood (4"+) verified this,
and on that class of wood the bowie's performance was only at about 40% of
that of the hatchet.

Even worse than the problem with raw penetration, because of the obtuse edge
and primary grind the bowie would glance far too easily. It could not cut at
the angles that you would want for optimal penetration and thus you are
forced to work at higher angles which will significantly effect penetration.
There were also problems with the handle. While I no longer found the grip
abrasive, the end hook is far too sharp and you can't drive off of it
without it generating excessive pressure on your pinky. As well some trials
with a bit of oil on the handle resulted in the blade becoming very unstable
in hand and being hit with a performance loss of about 40 %. The hatchet is
not as strongly effected as its chopping performance doesn't depend as much
on the followup drive after the blade hits the wood.

To clarify method, I was chopping felled wood at about waist height using
full force swings. I experimented with various contact areas along the
length of the blade on the bowie and found that for me the optimum
performance was obtained when I chopped pretty much right in front of the
choil. As I went out on the blade, yes the speed of the knife at the contact
point was increased, but I found that I could not drive as strongly into the
wood because of the leverage disadvantage and that the performance suffered
by about 15% at maximum. Of course if your chopping style is different so
will be the optimal impact point, if you chop depending more on speed then
you will want to move further out on the blade.

Ok, so the knife suffers a large chopping disadvantage, how does it cut? I
tested this by whittling six points on one inch hardwood dowels. The bowie
took 29 +/- 3 cuts to make a point. This is rather poor performance. The
blade does not bite in deeply into the wood and the thick profile forces a
lot of splitting of the chips. The Bruks hatchet easily outperforms the
bowie carving much larger chips, with less effort.

With the cutting done I then proceeded to modify the edge profile. First I
used a one inch belt sander to strip away excess metal from the edge which
was brought down to a 12-13 degree bevel. I also hit the primary grind a
few times, not enough to significantly remove any metal, but just to get a
feel for how much work it would take to put a full height flat grind on the
blade (more than I would want to do). After the shaping I used 15 micron
sandpaper to remove the burr and do a preliminary sharpening. After this
was finished (20 or so strokes per side), the blade would shave, but
roughly. I then cleaned up the bevel with some five Micron SiC, and finished
with some stropping on leather loaded with CrO, the blade would now have
smoothly. Because the leather gave somewhat under the sandpaper, this
introduced a secondary edge bevel of about 15 degrees over the last 0.04" of
the edge.

Back to the hardwood dowel, the bowie showed a huge change in bite, it now
sank much deeper into the wood. The blade removed much larger chips of wood
you could easily pick out the before and after chips. The bowie would now
point the dowels only requiring 14 +/- 1 cuts. This was a performance
increase of about 100%. Note that this result is a little skewed because of
the effect of fatigue, but only I would estimate by a few percent.

With the new edge profile I repeated the chopping. The Marine Raider bowie
showed an obvious improvement in penetration. Just a few chops showed it to
now be in the same class as the small hatchet. A total of 57 cuts (502
chops) produced a median performance rank of 95 +/- 4. This was almost a 50%
increase in chopping performance. Besides the raw increase in penetration, I
noticed that the problem with glancing was significantly reduced and I could
work with the angles just slightly higher than optimal. The obvious question
that came to mind was in regards to durability, however the edge suffered no
problems with the lower angle. After all the chopping the edge was not
visibly damaged. It could even still scrape one or two hairs off my arm on a
pass. Note this was not clear wood being cut either, I would estimate that
one out of every ten or so cuts was through a knot.

In regards to sharpening, the knife could still slice paper after the
chopping, although it had to be within 0.5 inches of the holding point to
start the cut. The edge feels aggressive, but requires about 3.5 cm to cut
through 1/4" poly under a 1000 g load. Checking the edge under magnification
reveals damage on the order of 0.05 - 0.1 mm, or 50-100 micron. The edge in
the damaged area looks to have been impacted/deflected. A quick session of
stropping (10 passes per side) on CrO loaded leather increases the
performance of the blade on the poly about 75%. Another session does little
to increase the performance indicating that the edge is in a near optimal
state of alignment, however with a significant amount of wear, and the
degraded sections (1-2 every mm), are giving a false sense of aggression
when the edge is checked with my thumb.

In regards to the exact edge angles used, what is optimal will depend on the
wood being cut as well as the technique used. If your technique is better or
the wood softer, you can go with a more acute angle without suffering a loss
in functional durability. As well consider that this is pretty much the
worst end of the spectrum in regards to steel performance, a higher grade of
heat treatment, as well as a higher grade of steel, should also allow a more
acute edge profile and longer edge life. Note that the edge was sharpened to
a high polish before the chopping and dowel cutting, if a rougher finish was
used then the edge would degrade much quicker as the micro-teeth broke off
under the impacts.

-Cliff

 

[Will York]

Nice work, Cliff. That's a very graphic demonstration of the effect of blade geometry on cutting performance, and serves to illustrate that applying the right edge geometry/finish for the task at hand is at least as important as selecting the right steel and heat treat. In fact, in terms of cutting efficiency with a fresh edge, I think your description shows that edge geometry and finish are the most important factors of all.

Thanks for your ongoing tutelage.

-w


(edited to add edge "finish" to edge geometry)

 

[Joe Talmadge]

Agreed! Great stuff as always.

Joe

 

[HUNTER3897]

Thanks Cliff. Very interesting stuff, as usual.

Jim McCullough

 

[Cliff Stamp]

WILL :

I think your description shows that edge geometry and finish are the most important factors of all.

Yes, the steel and heat treatment make no effect at all on the cutting ability of a particular geometry (*minor* effect on surface friction only) and only a very small effect in regards to edge finish and to see the latter you have to be working at very fine polishes (below the grain size of the steel) and at very acute angles.

There is some effect in regards to slicing ability as some steels are more aggressive due to the carbide structure, but this is completely swamped out by the edge finish. Even the most aggressive steel at a 8000 Japanese Waterstone finish will easily be outsliced by simple 1095 with an x-coarse DMT finish.

The type of steel and heat treatment will control edge holding and also the level of durability at a particular geometry. For example INFI won't break apart at that angle and thus the edge holding is much higher, it also has a greater wear resistance than 1095, but that is not the limiting factor in the above case, the edge isn't being worn away its being destroyed by the impacts.

What controls cutting ability in a blade is an interesting subject, one that I have been meaning to write up for some time. You have sharpness, cross section, gross blade issues (curvature), and leverage aspects controled by the grip. What is most interesting is that different materials focus different amounts of weight on the various aspects.

For example if you want to push cut through hemp rope under tension the blade much be very sharp as the rupture pressure of the rope is high, and the edge ground to a thin angle for the same reason, although this is a much lesser influence. Since the rope is being pulled apart it doesn't exert much force on the blade so the height (or thickness) of the edge doesn't make a lot of difference and the primary grind is pretty much ignored.

However if the rope is not under tension then the rupture pressure is still high so you still need a high polished blade with an acute angle, but now the blade starts squatting the rope along side of what it being cut and since the rope obviously resists such compaction it thus exerts a force on the blade, which is why you need more force as you start cutting into the rope. The amount of force required will be increased as the edge thickness increases as well as the nature of the primary grind (height and angle).

As an example of the complete opposite behavior. Cheese has a very low rupture pressre and can thus be penetrated by a very dull knife. However because it does not split (there is no internal tension and it is quite elastic and thus doesn't get plasticall deformed), it exerts quite a strong binding force on the blade due to the very high coefficient of friction. Thus to get high performance here you want a very acute primary bevel and a thin stock to reduce pressure on the flats as well as some way to eliminate the excess friction such as blade hollows. Sharpness and edge angle have a rather small effect.

Thanks for the comments all.

-Cliff

 

[Will York]

Cliff-

Great synopsis of the factors affecting cutting effectiveness.

When I look at the results of the ABS hammer-in competition on the current thread under Customs, I'm struck by the different kinds of cutting events and by the fact that two of the top three finalists used 1084 steel (John Fitch and Charlie Smale). The other, Ray Kirk who won last year, apparently used 52100. Of course, this is a forged-blade competition so you would expect these steels to be part of the mix.

But I was just wondering if you had any experience trying to determine if these steels, forged 1084 and/or 52100, might have special properties worth noting, that would allow them to take and hold especially thin edge geometries and/or finishes that would give them an advantage in this sort of competition. Or would you think that the strength and toughness of some stock steels such as INFI or CPM3V might actually give them the edge, if they were used in the same geometries employed by the ABS finalists, against the forged steels. Or, given your above thoughts, would you expect little difference at all between steels, whether forged or stock, as long as they would stand up to the edge stresses of the ABS contest events.

BTW, in reference to your above examples, I never expected to get such illumination from cutting the cheese--at least not without an open flame nearby.

Thanks again--Will

 

[Jerry Hossom]

Steel and heat treat do matter, since grain structure is a defining element in what kind of an edge a blade will ultimately take and hold. That's one reason why CPM-3V takes a great edge; it has the finest grain structure of most any production steel currently made.

I am a strong proponent of proper edge geometry, but it is greatly enhanced by good steel, and no steel is "good" without proper heat treating in my opinion.

 

[Cliff Stamp]

Will :

But I was just wondering if you had any experience trying to
determine if these steels, forged 1084 and/or 52100, might have special
properties worth noting, that would allow them to take and hold especially
thin edge geometries and/or finishes that would give them an advantage
in this sort of competition.

The outstanding property of 52100 is the fine grain structure, I have seen
it quoted in the 1-2 micron range, for comparison CPM-10V (a fine grained
steel) is around 2-6 micron , much more coarse. There are two primary
advantages to a fine grain size. First off, as noted in the above it
controls the limiting edge polish, but this is only a functional advantage
if you run with a really high polish and really low angles. Now while the
low angles criteria is obviously met, in regards to edge finish, it seems to
be rather coarse from what I know. A Fine India stone is about 50 micron
for example, even a coarse grain steel like D2 is only about 30 micron. Thus
the grain of the abrasive will mask the grain of the steel. The second
advantage of a fine grain size is that the finer the gain, in general, the
stronger the steel. This is obviously a functional advantage as the
stronger the steel the more the edge will resist rolling and thus the
thinner you can run it. Note there is one other issue which is surface
friction. this will be lower the finer the grain, but it is a very small
effect.

Or would you think that the strength and toughness of some stock
steels such as INFI or CPM3V might actually give them the edge, if they
were used in the same geometries employed by the ABS finalists, against
the forged steels.

Yes, while grain structure is one of the factors in determining strength
there are others and some steels will score much higher in these areas. For
example CPM-10V at 63 RC has a tensile strength of 375 kpsi. It would resist
edge roll much better than 1084 and 52100 at the 58-60 RC that I assume
these blade are probably being run. It would also have much higher
resistance to edge wear, but that is not going to be a factor in this case
because not enough cutting is being done to induce metal loss by wear
anyway. So then does this indicate that the optimal blade would be made out
of a very hard, very high alloy steel - well no because there are other
factors still.

The problem with running such a blade is that the toughness would be rather
low, it will handle all the low stress cutting (paper etc.) fine, and would
even take the chopping with prefect technique, but if you got a little
sloppy you could induce gross blade failure. As well it would not be a long
term dependable knife, so it is sort of "cheating" (personal judgement
obviously) because it is not something that could be repeated many times so
it sort of misleads on functional geometry. Equally important the ductility
of the edge would be rather low and it might suffer damage from bend
fractures.

However CPM-3V would look to be ideal. It has a very high toughness even in
the upper RC range (58-60), so there should be no edge damage from metal
failure, and it should resist rolling better than 52100 and 1084 and thus be
ground thinner. Phil Wilson tried a blade at 61/62 RC and was only able to
damage the edge by really flailing on a knotty piece of 2x4, it would have
easily handled clear wood chopped in a controlled fashion. Personally though
I would run it a little lower because as noted in the above I think it is
misleading otherwise - personal perspective obviously.

Along those lines I have a custom in CPM-3V on order from Phil, this is to
be the limit of cutting performance in a 10" class chopping blade. The
limiting factor in edge thickness is that the knife has to be able to take
forceful cuts through hard knots without visible damage. Phil is aiming at
an edge thickness of 0.02" or better. The problem will not be gross fracture
as the steel will be around 58/59 RC so it will not suffer failure from lack
of impact toughness or ductility, however the edge could ripple on a bad
cut, or a knot that fractures or breaks out of a cut and thus induces a
large lateral impact across the edge. Prototypes will be used to explore the
limiting edge geometry.

Or, given your above thoughts, would you expect little difference
at all between steels, whether forged or stock, as long as they would
stand up to the edge stresses of the ABS contest events.

This is the critical part, the main advantage of another steel is going to
be can you run it thinner, i.e.. does it have enough or an advantage in
strength and durability to make it functional at a thinner geometry. Hell of
a question Will.

One last point, and I really can't stress this enough. The makers that
compete in the cutting competitions like Ray Kirk and John Fitch are at an
extreme level of cutting ability. The loads that a blade "sees" during use
are dramatically effected by the level of skill of a user. I am not talking
about small effects like 5% either, skill differences can easily be on the
order of 100%. One of the reasons these makers can grind the blades as thin
and acute as they do is quite simply because their skill is as extreme as
the edge geometry of the blades.

-Cliff

 

[Will York]

Cliff-

Those are intriguing comparisons of steel properties--thanks.

Originally posted by Cliff Stamp
One of the reasons these makers can grind the blades as thin
and acute as they do is quite simply because their skill is as extreme as the edge geometry of the blades.

I started to address that point earlier, but figured it was a given--these guys obviously have developed the art of blade handling to an extreme degree, comensurate with their abilities at the forge and wheel.

Jerry-

Thank you. Your points are well worth making, and I certainly didn't mean to discount the value of steel and heat treat--only that their roles can be far out-weighed by geometry and finish, in terms of cutting performance. I once thought that steel quality alone, if sharpened to the extent that a blade would shave hair, was the defining aspect of a blade's performance. From posts I often see here on the forums, I think many still hold to this notion. I realized some time ago from my own testing and the insights of others that this is a gross error.

One of the performances I was thinking of, when addressing the point about geometry, was your own technique of putting an acute convex edge on an Ontario machete. I now use that same technique to enhance the performance of my machetes, and it's an eye-opening--really amazing--improvement, for which I am in your debt. As you've demonstrated yourself to many non-believers, an Ontario with this edge will outcut much more expensive blades, made of much better steel, though the thin edge on Ontario's relatively soft 1095 steel is not durable enough for extended high-impact use.

For me, on a $20 machete, blade longevity is not an issue. When I ripple or break a blade, I just plunk down another $20 and go again. But I always look first at steel and heat treat before investing in a good blade--in fact, some makers have even labeled me a steel snob.

Thanks again for the insights.
--Will

 

[Cliff Stamp]

Will :

I once thought that steel quality alone, if sharpened to the extent that a blade would shave hair, was the defining aspect of a blade's performance.

Yes, this misperception is mainly caused by how knives are promoted. For example take a Boye Hunter in Dendritic 440C. Now do some slicing with it and a average production folder. The knives are worlds apart, not a little difference like 5% but the Boye blade will outcut the other multiple times to one, and outlast it in regards to edge retention. This performance increase is real, and can be duplicated by anyone who wishes to work with the blades. However what is the root cause - is it the steel or the "dendritic" nature. No, it is the geometry.

Boye grinds his blades down to basically nothing and then puts a secondary bevel on them. You end up with blades that are about 0.005" to a maxiumum of 0.01" thick behind the bevel. Thus the extent of the edge, which is the thickest and thus worst cutting part of the blade is minimized. On top of that Boye recommends sharpening his blades on a 600 grit Diamond hone. This will leave the edge in a very aggressive state (regardless of the steel), and thus produce a huge difference in slicing ability simply because of the difference between the slicing performance of that grit and the common buffed one.

The edge retention is also a bit misleading because cutting tests are done to indicate edge retention and if the Boye blade cuts better than the other, then even at the same level of blunting it will still readily out cut it. Therefore even if it had no real advantage in inherenet edge retention it would appear to have one simply because of the huge advantage in cutting ability.

Now I don't want to give the perception that steel type and heat treatment are irrelevant, such is hardly the case. Simply that they only effect cutting ability by a very small amount for the various reasons in the above, the contributions they make are in general completely masked by geometry and blade finish. However as Ed Caffery has noted you have to look at the whole picture, while geometry controlls cutting ability, steel and heat treatment control geometry.

-Cliff

 

[Will York]

Originally posted by Cliff Stamp
For example take a Boye Hunter in Dendritic 440C. Now do some slicing with it and a average production folder. The knives are worlds apart...However what is the root cause - is it the steel or the "dendritic" nature. No, it is the geometry.
Boye grinds his blades down to basically nothing and then puts a secondary bevel on them. You end up with blades that are about 0.005" to a maxiumum of 0.01" thick behind the bevel.

Cliff-

As you know, I'm a Boye fan, and I was certainly impressed to find from your past reviews of his blades that his edges were as thin as 0.005". But it didn't occur to me that this was the controlling factor in his knives' performance until you made the above point. I assumed from the extreme cutting efficiency of his blades that I was enjoying the "micro-serration" effect of the large “dendritic” chains of hard carbides in his cast 440C. I also assumed this was an anomaly in cutting efficiency that demonstrated there was more to good cutting ability than fine grain structure, which is typically touted as being so important to obtaining "fine" edges.

Your hypothesis is intriguing to me on a couple of fronts.

First, I believe there is some evidence that the vanadium carbides in CPM steels do have a more aggressive slicing action, in the same geometry and finish, than steels with no vanadium carbides. I believe you have commented on this yourself, in your review of the 10V Coyote Meadow. I know that Rick Dunkerley’s experience with 52100 and 10V also tends to bear this out. He has mentioned that his 10V blades are more aggressive cutters in the same geometry as his 52100 blades, and his 52100 has been laboratory-analyzed at 1/2 to 1 micron hard-carbide size at the edge. I wonder if a similar "toothy" action might not be at work in the performance of Boye’s steel, as he obviously believes and advertises.

Secondly, if all that is at work in Boye’s blades is thin edge geometry and aggressive finish, then it would seem we are currently experiencing far lower cutting efficiencies from most blades than should be available. I base this on the assumption that Boye’s cast steel should be weaker than forged steels, and if he can get such cutting efficiency out of a cast steel just by going to a thinner edge, then the stronger forged/wrought steels should offer a platform for even thinner edges and greater cutting efficiency, with similar strength and toughness as Boye blades. Boye’s steel does seem to stand up very well in comparison to others in his utility-size blades, at least in my experience.

Comments?

Thanks--Will

 

[Samurai6]

Will,

I am a Boye fan also, I almost always have a folder in my pocket, and my favorite hunter is the Boye drop-point. I long ago stopped attributing the superb cutting efficiency to the BDS steel though. I came across a couple of ATS-34 blades that cut just as well, and these were knives that had be cryo-treated and triple tempered to keep grain size as small as possible.

I do think the dentritic grain structure enhances the wear resistance dramatically. I have a few standard 440C blades, and they don't hold an edge anything like the BDS blades. Cliff has looked at BDS performance a lot more scientifically than I have though.

But to try to correct the topic drift a little bit: cutting efficiency is geometry, geometry, geometry.

 

[Will York]

Steve-

Your thoughts, together with Cliff's other current thread on grain size and finish, made me re-read Cliff's comments above, especially re-considering the following.

Originally posted by Cliff Stamp
There is some effect in regards to slicing ability as some steels are more aggressive due to the carbide structure, but this is completely swamped out by the edge finish. Even the most aggressive steel at a 8000 Japanese Waterstone finish will easily be outsliced by simple 1095 with an x-coarse DMT finish.

Makes sense. Even if the grain structure of the Boye steel were more aggessive than another given steel by comparison, the effect should be less an influence on slicing ability than the size grit of the abrasive used to finish the edge, when the abrasive grit is significantly larger than the grain size of the steel.

Also, Rick Dunkerley's experience with 10V vs 52100 I know is based on similar geometry and edge finish being applied to both. Whatever enhanced aggressiveness might be apparent in the 10V over the 52100 at a given edge finish, if the edge finish grit used on the 52100 were coarsened sufficiently, it should produce an edge that would have greater slicing aggressiveness than the 10V at the 10V's "normal" polish.

I'm still intrigued by your comment on the edge-holding ability of Boye's dendritic steel, though, and your experience mirrors my own. How a cast steel, with it's resulting relatively soft matrix, can hold an edge longer than forged steel, is an explanation I'd enjoy seeing.

Thanks all.

-w

 

[Cliff Stamp]

Will :

I assumed from the extreme cutting efficiency of his blades that I was enjoying the "micro-serration" effect of the large ?dendritic? chains of hard carbides in his cast 440C.

As Steve noted, its all in the geometry, with a secondary consideration on edge finish. Joe Talmadge has illustrated this very strongly with some of the work he has done on various blades. For example just by doing a slight profile on an Axis Lock from Benchmade to a 15/20 edge, and leaving the finish partially at the coarse rods, he was able to generate a 500-700% (not sure on the exact number, but I am sure its in that range) increase in slicing performance on poly. Just think about what that means for a moment. That is the same steel, same heat treatment, yet after sharpening the blade outperforms the NIB one many times to one. A 100% increase in tool performance is extreme, a 500% one is unheard of. That shows rather dramatically, the poor NIB edge optimization. This is one of the reasons I promote ignoring the NIB edge geometry and finish (unless the blade is a custom that you have designed as in that case you should have specified the optimum conditions).

I also assumed this was an anomaly in cutting efficiency that demonstrated there was more to good cutting ability than fine grain structure, which is typically touted as being so important to obtaining "fine" edges.

It is not an anomaly as such. There are two broad classes of cutting, slicing and pushing. The complication, performance wise, is that for optimal ability they desire pretty much on the exact opposite steel structure thus you can't have both in the same blade. It also means that which one is better depends on what is the majority of type of cutting the blade will have to perform. There are some more comments along these lines on the other thread currently running :

http://www.bladeforums.com/forums/showthread.php?s=&threadid=176372

Secondly, if all that is at work in Boye?s blades is thin edge geometry and aggressive finish, then it would seem we are currently experiencing far lower cutting efficiencies from most blades than should be available. I base this on the assumption that Boye?s cast steel should be weaker than forged steels, and if he can get such cutting efficiency out of a cast steel just by going to a thinner edge, then the stronger forged/wrought steels should offer a platform for even thinner edges and greater cutting efficiency, with similar strength and toughness as Boye blades. Boye?s steel does seem to stand up very well in comparison to others in his utility-size blades, at least in my experience.

Yes, this is a point I have been driving at for quite some time. A better steel doesn't inherently make a better knife. If you just duplicate the geometry the higher grade steel will effect little change in cutting ability of the blade, it was nothing but a waste of time and money to use unless of course you wanted a more durable blade. The edge retention will be increased of course as will the corrosion resistance in some cases, however there is a tremendous potential being wasted. A higher grade steel should allow a high grade geometry, and as simple as possible that means in general just thinner.

Back to Boye, he grinds his blades down to nothing and just puts a hint of an edge on them. The blade is then just 0.005" - 0.01" behind the edge which is ground at about 18-22 degrees or so. You can't really improve on the edge thickness as it is barely there, however you can decrease the edge angle. I have a blade in CPM-3V from Ed Schott that has an edge formed from a 10 degree bevel (20 included), I have done hard chopping with it with no problems, so if you were just using it for cutting, even hard cutting, that would be overkill. For a small 3V blade I would be personally try 0.005" behind the bevel ground at about 7.5 degrees per side or lower. Of course I would also use a more acute primary grind, which would result in a thinner stock, 1/8" with a full taper, 1/16" if not.

The other consideration is of course durability. In the above I put forth the perspective of a better steel offering an improvement in cutting ability by altering the geometry. There is another viewpoint - given the same geometry a better steel will make the knife functional over a broader range of tasks. For example I have a 52100 blade forged and heat treated by Ed Caffrey, which has a very similar edge profile as the Boye hunters. I have used this 52100 blade to split knotty wood (cutting through the knots) by pounding on it with a stick and cut through poultry bone under 100+ lbs of force. The edge was undamaged. I don't think Boye's hunter would react very well to similar cutting.

How a cast steel, with it's resulting relatively soft matrix, can hold an edge longer than forged steel, is an explanation I'd enjoy seeing.

In regards to pure push cutting if regular 440C (at similar geometry) was compared to Boye's cast version, every thing would point towards the regular 440C version outperforming Boye's. This is of course assuming a full heat treatment for the regular 440C including a slow deep cryo and post temper giving it a RC of about 59. However in regards to slicing the performance could be a bit different. Boye's cast version should be both weaker and less ductile so the edge will deform and take damage more readily (which is why it should be outperformed at push cutting), however the inherent nature of the steel might give a high slicing ability even with a more degraded edge. Especially if the structure of the cast steel is needle like because tempered martensite (most modern cutlery) is spherical, obviously not the optimum for aggression.

After reading over the work I have done with Boye's blade what stands out to me as fairly extreme is how the Boye Dendritic Cobalt stood easily alongside the Deerhunter in AUS-8A, and on average slightly outperformed it. Now at the time I think I was of the mind set "well, its AUS-8A, that not a great standard anyway". But forget all of that, AUS-8A is still a 55-57 RC steel and the cast Cobalt is like what ~35 RC. The Cobalt should fold over pretty much right away and not be in the same class, but it doesn't. I think that is a pretty extreme case because of the percentage of alloy components being so extreme in the Cobalt blade. Another interesting point is that while I always found the Dendritic 440C to be a better edge holder than the Cobalt it was only about 25 +/- 10 % (just eye balling some of the numbers). I assume however that the RC difference in these two materials is much larger, then again so is the alloy composition which might balance that out somewhat.

In addition I just read over the work with comparing the other Cobalt blades against the Dendritic cobalt one and the latter does very well. This makes little sense as the alloy contents are similar and thus you are directly comparing a cast alloy to one that is forged. The Boye cast Cobalt should not be in the same class as the Stellite 6K one and the forged 6BH blade, yet it easily is, and at times even comes out slightly on top. How is this possible? I think there are two large factors. First off all the edge angles are fairly thick ~20 degrees per side, this will greatly enhance the resistance of the edge to rolling which is the cast blades greatest weakness. Secondly all the finishes I used when comparing the Cobalt blades were very rough, this again vastly reduces the effect of edge roll (the larger the teeth the more they can be distorted and still have a coherent cut path). It would be interesting to look at the Boye cast Cobalt against Stellite 6K / Talonite with a fine edge, say 10 degrees per side at a high polish.

And of course the critical information is the hard data on the exact nature of Boye's Dendritic 440C? I am assuming as are most people that it is soft and weak. However what exactly is the structure of the steel? Is it in fact just regular 440C? How large are the carbides? How uniform is the composition? What are typical RC values? Tensile strength? Impact toughness? Without some of this data it is hard to come up with a concrete explanation. In any case I think Boye deserves recognition for thinking laterally and producing a valuable addition to the cutlery industry.

-Cliff

 

[Will York]

Thanks, Cliff--

I don't know how many times I've asked you the same questions from different angles, and your patience, as always, is appreciated. I may even be learning something here!

Your thoughts from above:
"the inherent nature of the [Boye dendritic] steel might give a high slicing ability even with a more degraded edge. Especially if the structure of the cast steel is needle like because tempered martensite (most modern cutlery) is spherical, obviously not the optimum for aggression."

That was what I was looking for. Whether there might be something intrinsic in the steel structure that could enhance the cutting effectiveness, a la the vanadium carbides in the CPM steels, which develop that "toothy" cutting effect. This could also account for the long edge life experienced by Steve and myself with Boye blades--the edge may still cut well even after it degrades, because it is so thin and the steel's inherent nature so "toothy".

I do realize there's a difference between optimal push-cutting finish vs. optimal slicing finish, but I also notice that with a fresh edge, the Boye steel will push cut very effectively, while still retaining that "toothy" slicing action. I assume that's the result of the very thin edge combined with either an aggressive finish or the inherent toothiness of the steel. I've experienced similar cutting action from a CPM420V blade, ground extra thin for me by Randy Martin, which will push-cut through sisal rope like a polished razor, yet retains a very aggressive slicing action. Seems to me to be a very effective combination, whatever is at work there--very good push-cutting plus exceptional slicing action.

Best regards,
Will

 

[Cliff Stamp]

Will :

This could also account for the long edge life experienced by Steve and myself with Boye blades--the edge may still cut well even after it degrades, because it is so thin and the steel's inherent nature so "toothy".

Yes, I think it is the geometry that is the critical factor here and not the actual state of the edge. It is critical to note that the difference in cutting ability between one of Boye's blades and a typical "tactical" knife is not something small like %10, it is huge. For example One of Boye's hunters can push cut through 3/8" poly at about 45 +/- 5 lbs. I have seen blades that don't make it halfway under 250 lbs of applied load.

When you push cut something there are two components to the force that the material exerts on the blade. The first is the force required to cut the material and this is dependent on the type of material and the sharpness of the edge. The second component of the force is due to the binding force along the sides of the blade do to the resistance to compaction by the material. For most materials the second component is far in excess of the first. This means that geometry can have a far greater influence on edge retention (measured by gross cutting abilities) than actual steel properties in a lot of cases.

For example if you take one of Boye's blade and press it into the 3/8" poly you will find the edge biting in with just a few pounds of force, lets say 4.5 lbs are required, then this is only 10% of the total applied load. Now lets assume that the blade is blunted to the extent that this is doubled to 9 lbs, the total force required is now 49.5 lbs. This means that the effect you see in total is only a loss of cutting performance of 10%. Not that significant, yet the blade has blunted down to 50% of its optimal sharpness.

It takes an extreme level of blunting to decrease the level of cutting ability significantly for most materials because of the strong geometrical influence. For example even if the edge blunted down to 10% of its optimal performance, this would only reduce the cutting ability on the rope to about 50% of its optimal performance. Now you would indeed notice the performance had decreased however it would still be in excess of many other blades freshly sharpened.

I also notice that with a fresh edge, the Boye steel will push cut very effectively, while still retaining that "toothy" slicing action. I assume that's the result of the very thin edge combined with either an aggressive finish or the inherent toothiness of the steel. I've experienced similar cutting action from a CPM420V blade, ground extra thin for me by Randy Martin, which will push-cut through sisal rope like a polished razor, yet retains a very aggressive slicing action.

Slicing is more complicated to study than push cutting as it is not as simple. In essence when cutting something you exert two forces on the blade, one which is straight into the material and once which is across it. If there is no across motion (no slice) then you are doing a 100% push cut. However you can't eliminate the push cut completely and do a 100% slice as there has to be some component of force pushing the blade into the material. Thus slicing performance is strongly correlated to push cutting ability. Specific to Boye's blades, this means the extreme push cutting ability will provide strong slicing ability even at a high finish.

In a rather extreme example, take the blade with the edge described in the following :

http://www.bladeforums.com/forums/showthread.php?s=&postid=1446725

Considering the level of polish (stropped for hundreds of passes on CrO) it should slice horribly, however because of the very high level of push cutting ability (8.3 degree bevels), it will "slice" very well. In essence what is happening on a slice is that the blade can actually pretty much push cut straight through most materials, even hard ropes, will little resistance and thus the "aggression" of the edge is really high. Of course if I left that blade at a coarse finish it would slice better, however compared to a blade with a thicker ground edge, it will out-slice it even at a finer finish.

-Cliff

 

[Will York]

Cliff-

That description of the relative loads required for penetration by obtuse vs. acute edge geometries, as compared with the effect of edge degradation due to blunting, is very illuminating.

I think your descriptions become more refined as you explain these relationships over and over, and the message becomes clearer each time. Either that, or by repetition your incisive words are cutting gradually deeper into the dense fog that is my brain.

Whichever it is, thanks again.

-Will

 

[Cliff Stamp]

Here is an interesting thread concerning Boye's steel :

http://www.bladeforums.com/forums/showthread.php?s=&threadid=177396

note this part :

this needs to be Heat treated, normally just like 440C

This was one of the questions I had about Boye's steel. When comparing cast vs forged products (in general) neither get a post-forming heat treatment. It seems that Boye's does and this could example the lack of problems with his "cast" blades.

I tried to find out expactly what Boye does for his blades but the main pages have been removed and his new website doesn't have much information on it. It seems he is now strongly into his Cobalt dive knives.

Will, our interactions have had a great impact on the refinement of my perspective, the magnitude of which is quite comparable to the influence of the work it is based on.

-Cliff