Various Cobalt blades by David Boye (Dendritic Cobalt), Kit Carson and Steve Schwarzer (Forged Cobalt 6BH), and one from Gerber in Stellite 6k


Specifications

These blades were on loan from Will York for a review. The Dive knife is made from David Boye out of cast Cobalt, and is essentially a thicker version of his "Basic #3" . Some information from the maker on the Dive knife :

The Boye Cobalt Dive Knife is a non-ferrous, non-magnetic, wear-resistant and salt water corrosion proof material. It will not rust. Our unique casting process creates a blade which holds an edge even longer than dendritic steel. The non-magnetic nature of cobalt means the knife won't affect a compass, so you can wear it anywhere. Each knife comes with a brass lined nylon sheath.

and on the Basic series :

Boye Basic Knives combine maximum utility with simplicity of design. This is simply everything you will ever need in a knife. They are easy to carry, efficient to use, slender, sturdy, totally versatile, "hand - friendly," and go unnoticed on a belt. Features include: 1- A completely cast knife made entirely of Boye Dendritic Steel for superior edge holding and quick sharpening, 2- a dropped edge blade shape which puts the blade down below the fingers where you want to do the work and forms its own fingergaurd and sharpening angle guides, 3- unique I-beam architecture with thick, strong, continuous, one-piece integral construction, hollowed handle sides for lightness and strength, a "flat" configuration which makes the knife unobtrusive and easy to carry. In addition each knife comes with a flat, brass-lined nylon sheath.

no such information was available for the other knives

The following table lists the specifications for the three blades. Dimensions are in inches, weight is in grams, and the angles are uncertain to about 1-2 degrees.

Some relevant geometrical aspects
Knife Weight Blade Edge
Length Thickness Width Angle Thickness Width Angle
grams inches degrees inches degrees
Dive Knife 154 3.95 0.30 1.45 6 0.015 0.020 21
Forged Cobalt 308 5.05 0.21 1.25 4 0.045 0.071 18
Stellite 6K 187 4.80 0.15 1.23 3 0.011 0.015 20

The forged blade is much more massive and is significantly thicker behind the edge bevel than the other two knives indicting a optomization for heavier use. The Boye Dive knife has a very thick spine, but thins to the expected very efficient cutting edge that Boye applies to his knives. The Stellite 6K blade has in general the most optimal cutting profile, while it had a slightly more obtuse edge than the Boye blade, the primary grind is much thinner. As for materials, all these blades are similar.

The Boye blade is cast Stellite 6 cast, creating "Dendritic Cobalt", which essentially has large segregated carbides at the cost of a lowering of ductility and toughness. The Stellite 6K blade has about 0.5% more carbon than Stellite 6 and is also forged and rolled to increase strength. The forged blade is Cobalt 6BH which is Stellite 6 which has been hot rolled and age hardened (same thing as Talonite, just a different name). The forging may have effected composition and structure.

A side shot :

From the top

Note the warp in the Gerber blade. This was tested alongside another sample on loan from Dennis Saccher (Cobalt on Bladeforums) which didn't have a warp, and it was found to not significantly effect most types of cutting. A shot of both :

and from the top

Rough ranking of cutting ability and edge holding

Using the Boye Dive knife and the forged hunter rolls of abrasive fabric were were sectioned. The number of slices used to cut through the roll taken as a measure of sharpness and it was averaged through four consecutive trials :

Cutting ability and edge retention comparison between Boye Dendritic Cobalt and forged Cobalt 6BH on abrasive fabric
Blade Finish number of rolls cut
2 6 10 14 18
BDC 220 SiC   1.5 (1) 2.4 (2) 2.3 (3) 2.3 (4) 2.4 (1)
6BH   1.6 (1) 1.9 (1) 2.0 (1) 2.3 (2) 2.2 (1)
 
BDC 600 DMT   1.7 (1) 2.9 (2) 2.8 (3) 2.6 (2) 2.6 (2)
6BH   1.9 (3) 2.1 (2) 2.7 (3) 2.2 (2) 2.4 (1)
 
BDC 800 AO   4.3 (3) 4.1 (4) 4.8 (3) 4.6 (2) 5.6 (5)
6BH   4.5 (4) 5.5 (2) 6.0 (1) 5.6 (3) 6.6 (2)
 
BDC 800 CR 46 (10)  
6BH 65 (  8)  

As general comments, the blunting is nonlinear and decreases as more material is cut and greater slicing ability and edge retention are seen on the rougher grits. On the last run with the very high polish the first four runs showed heavy blunting. For the Dive knife; 23.5, 42.0, 58.0, 60.0 slices were required, for the forged blade; 48.0, 64.0, 66.0, 80.0. However in regards to separating the two blades, since the force used to make the cuts was the weight of the blade and the forged knife was heavier and as well longer the above indicates the Boye blade showed better edge retention and aggression. The Stellite 6K blade and the forged Cobalt knife were then compared on denim using the same methods:

Cutting ability and edge retention comparison between a Gerber Stellite 6k blade and a forged Cobalt 6BH knife on denim
Blade Finish Number of rolls cut
2 6 10 14 18
6K 600 DMT 4.2 (1)   4.6 (3)   4.6 (3)   4.6 (5)   4.0 (8)
6BH 7.5 (4)   9.3 (8)   8.7 (9)   9.1 (1.3)   8.8 (9)
 
6K 800 CR 4.8 (8)   7.6 (5)   8.9 (1.1)   7.9 (1.6) 26.0 (1.4)
6BH 9.1 (1.9) 12.2 (8) 11.0 (6) 16.8 (1.7) 27.0 (2.4)

Here, the initial aggression is quite similar for both finishes in contrast to the previous fabric. This is is because the denim is much easier to cut thus the blades pushed through it a significant amount. The 6K blade shows a consistent advantage in terms of aggression and in edge retention when considering the longer and heavier forged blade. All three blades were next checked for edge retention on cardboard. All were freshly sharpened on a 200 grit silicon carbide waterstone. The sharpness was measured by slicing rolls of a harsh synthetic fabric, with an average taken of four sections of a roll cut.

Cutting ability and edge retention comparison between Stellite 6k, a forged Cobalt 6BH and Boye Dendritic Cobalt on cardboard
Blade Finish Initial performance Amount of cardboard cut Final performance
6K medium 4.8 (1)  500 cm 5.1 (2)
6BH 5.0 (2) 6.2 (2)
BDC 4.5 (1) 6.0 (2)
 
6K coarse 2.6 (2) 1000 cm 4.8 (2)
6BH 2.3 (1) 7.2 (3)
BDC 3.6 (2) 7.6 (3)

Consistent with the other runs, the Stellite 6K has better edge retention. This is consistent with the higher carbon content, HRC measurements and tensile strength. The more coarse finish also had much better slicing aggression with all blades and better edge retention. These properties were also checked using Using rope as a blunting stock instead of cardboard. The fabric used to benchmark the cutting performance was fairly difficult to slice and nearly impossible to push cut :

Cutting ability and edge retention comparison between Stellite 6k, a forged Cobalt 6BH and Boye Dendritic Cobalt on 1/2" poly rope
Blade Finish Initial # of rope cuts Final
6K 220 DMT 5.8 (3) 25   7.7 (2)
6BH 7.7 (5) 35    (3)
BDC 7.6 (3)   8.7 (3)
 
6K 600 DMT 4.3 (2) 30   4.6 (1)
6BH 4.7 (4)   6.2 (3)
BDC 6.7 (4)   6.5 (4)

The 6K knife again has better edge holding performance. Here better performance was seen from an initial sharpness and edge holding perspective by the finer finish because the cuts were made on more of a push than a slice.

Slicing ability

The cutting ability of the knives was compared by pointing a piece of Hickory which was 1/4" thick and one inch wide. Points were made through a one and two inch length with the number of slices required used as a measure of the cutting ability. A deerhunter from A.G. Russell was used for a reference.

rough whittling ability on hickory
Model one inch cut Rating two inch cut Rating
Gerber 6K 5.8 (6) 100 2.3 (4) 100
Deerhunter 6.5 (3)   88 ( 9) 2.8 (2)   82 ( 16)
Dive knife 8.3 (3)   70 ( 7) 5.5 (7)   42 (   9)
Forged 6BH 10.8 (3)   53 ( 5) 7.5 (7)   31 (   6)

Note that the thick spine of the Boye dive knife is not nearly as costly to performance as the thicker edge on the forged 6BH blade. This is because the force of wedging is focused around the edge. In addition with the cuts were made longer the performance of the lower blades dropped significantly. This is just due to more wedging taking place in deeper cuts. The Gerber's advantage over the Deerhunter was significantly influenced by the longer blade length,as the wood was so hard the blades could skate a little during a slice gving an advantage to blades of longer lengths. To examine the influence of variety of wood, the cutting was repeated with Pine sticks, a one inch cut length was used.

rough whittling ability on pine
Model Performance Rating
Deerhunter 10 (1) 100
Gerber 6K 13 (1) 73 (7)
Dive knife 19 (1) 52 (4)
Forged 6BH 26 (2) 37 (4)

As expected the Deerhunter pulled ahead of the Gerber blade and the rankings of the Dive and forged blade were much lower than they were on the Hickory cutting with the one inch cut used. The softer the wood the deeper the cuts and the more the primary grind is a factor so slimmer blades will draw further ahead.

Handle ergonomics

The Boye Dive knife has a flat metal slab for a handle and it is very uncomfortable during any heavy work. During the above wood whittling a glove had to be used. Even though it doesn't cut as well, the forged blade stands out over the dive knife for more extended work due to the much greater handle ergonomics.

Summary

Overall, the blades are similar in edge holding abilities, however the 6K generally has the advantage in the Boye blade which in general out lasts the forged blade considering the greater mass and length of edge used. The cutting ability is much more significantly different with the Gerber blade readily outcutting the other two because of the thinner blade stock and more efficient edge geometry. The Dive knife will out cut the forged 6BH knife due to its much more thinner edge which can compensate for the thicker stock. In regards to handle ergonomics the perforamnce is completely reversed with the forged blade clearly ahead followed by the Gerber blade and the Boye Dive knife way behind.

Update : this review was written back in 2000 when most of the personal techinques for comparing knives were being developed, current methods are much more robust. However even with the above crude comparisons, there were still many issues raised such as the influence of grit finishes on push/slicing performance and the influence of edge and primary blade geometry on cutting ability.

Comments and references

Comments can be sent to : cliffstamp[REMOVE]@cutleryscience.com.

There is also a website for http://www.stellite.com Deloro Stellite and Marion Poff has probably the largest collection of Talonite information on the web, another Cobalt based alloy being used in knife blades.

The Stellite 6k knife from Gerber was featured in an article in Knives Illustrated, April of 1996, the article title was "Stellite Knives A new limited edition knife looks real good". The author was M. C. Adley. The forged Stellite blade was the subject of an article in Blade, January of 1999. The title was "First-ever forged Stellite Blade?". The author was Steve Schwarzer.


Last updated : Aug : 2003
Originally written : 2000
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