Knife review : Small Sebenza


The review consists of :

Paramilitary (top), small Sebenza (bottom)

Specifications

The small Sebenza has a blade length of 2.94" made by stock removal out of S30V stainless steel hardened to 58/59 HRC. The handle is 6Al4V Titanium. It weighs 80 g and has an overall length of 6.875" opened. The blade is 0.118" thick and 2.2 cm wide at maximum with a 1.75 cm high primary hollow grind which tapers to an edge ground at 0.012-0.014" thick and beveled at 14.6 +/- 0.9 degrees per side. The primary hollow grind is very deep, 1/8" back from the edge the blade is only 0.018" thick, 1/4" back the thickness has only increased to 0.025".

Stock testing

New in box the small Sebenza could shave, but not perfectly smooth and not close to catching hair above the skin. It could cut newsprint on a draw but could not make a push cut. On light thread it took 125 +/- 12 grams to make a cut and was significantly sharper through the tip than near the choil, on light cotton the aggression was low, under 200 grams of tension the small Sebenza needed 0.68 +/- 0.04 cm of edge to make a cut.

With the new in box edge the small Sebenza push cut 3/8" hemp with 22.5 +/- 1.0 lbs and had no aggression on a slice which corelates well to the cotton performance which also showed low slicing aggression.

Whittling hardwoods, the Sebenaza did well able to make a one inch point on basswood in 6.1 (5) slices.

The point on the small Sebenza is 0.725" wide with a 1.09" taper at 3.1 degrees. The point has high penetration ability which is readily illustrated by some phone book work. The Sebenza achieves 229 +/- 4 pages with a 50 lbs push, and 664 +/- 26 pages with a hard vertical stab.

food preperation

As a paring knife, the cutting ability is high due to the thin and narrow edge and the deep primary grind. It peels potatoes well, cutting with light force and comfortable in hand due to the edge being close to the grip so there are no leverage issues. The handle is also well suited to the sideways grip normally used for paring and similar cutting. The point is fairly fine and easily performs precision coring, removing small defects in potatoes and root stems. This is one of the better folding paring knives seen for such work, in the same class as the U2. The only real negative is that the initial edge angle is more obtuse than necessary.

As a general utility knife the small Sebenza works well on soft vegetables, easily dicing up a green onion and can dice up an onion readily slicing sideways unlike some thicker knives which require the onion to be on its side to make the necessary cuts. It also efficiently sections some carrots. The main issue with its performance is just lack of length and position of the edge which reduce performance for extended cutting. For this type of work when a large volume has to be cut then a dropped edge is much more efficient as it allows full cuts through the cutting board. Similar a longer edge with more belly will allow more of the edge to perform the cutting.

In slicing up the thicker vegetables the hollow grind tends to wedge excessively. On potatoes while the japanese utility from Lee Valley makes thin slices with about a pound of force, the small Sebenza takes around five. On vegetables which tend to crack and open up a little more it does much better in comparison. On small to medium carrots where the japanese utility takes around three lbs, the small Sebenza is still around five. The small Sebenza is also too small to work well on deep cuts of meat or thick slices of bread, just a limitation on blade length mainly.

On grasses and light brush the small Sebenza cuts well when sharp however as with any blade this short efficiency is low. The performance can be raised by by lashing it to a piece of wood which gives more reach, such as was done with the Meadowlark. However with the small Sebenza, the very deep primary hollow grind could induce gross failure if the grasses and such were covering a rock. On woody vegetation the small Sebenza has little mass and thus can't chop woods effectively, and using it with a baton would be problematic as the thin edge would not react well to knots, however it cut down softer woods by simply slicing into them. The slicing ability is very high as noted on the stock whittling work and the small Sebenza easily takes a piece of pine and converts it into a pile of shavings for tinder :

Miscellaneous

On some plastics, the small Sebenza took 72-78 lbs to go through the bottom of the two litre bottles. A glove was worn as the handle was hot spotting due to the open frame structure and was very uncomfortable. For reference, K2 took the same force to make the cuts. While the K2 has a significantly thicker primary hollow grind, the edge is significantly more acute which compensates. This plastic cutting, while not appearing to be that difficult as plastic is after all much softer than the knife, is actually fairly demanding as if the knife twists under the heavy force as it is worked through the thick plastic it can induce basically a hard prying action across the edge which on hollow ground blades can remove a piece of the primary grind. Thus to do such cutting with minimal stress on the blade the plastic should be held very firmly in place to prevent it from moving and thus the blade twisting. Just cutting the sides of the bottle and even on much thicker plastic like 5 gallon buckets in comparison doesn't significantly load the edge even if the blade twists a little because the plastic is much thinner and softer and thus can't act like a vice and hold the edge in place.

On some light metals, the small Sebenza cut through a pepsi can with visble edge damage or in fact no significant blunting. However cutting open a large apple juice caused the edge to visibly reflect light. The edge had chipped, about 0.1 mm deep when checked under magnification. A piece was then cut out of the side of the can. This took about 20 lbs (can was cut on a scale), much more force than was used opening the top. It was also really difficult to cut in a controlled manner as the can is ridged and it is thus easy to twist the blade. This cutting broke a small piece of the tip, just a fraction of a millimeter, the edge was chipped out in several places, 0.2-0.3 millimeters deep.

UPDATE : In general it is hard to judge the performance of a knife from this kind of work aside from a rough judgement because so much of it depends on how the cutting was done. Much later after this cutting was performed a significant amount of time was spent cutting light metals and it was found that if the cutting was done so as to minimize side loading, making it essentially just a compression action, it was possible to do such cutting with very thin edged knives. It would have been informative to have another knife used as a reference for this can cutting.

Edge retention

Before any comparative work was done the small Sebenza was reground to approximately 10 degrees per side to make the edge geometry more consistent with the other personally owned blades. First the small Sebenza was used alongside a Manix which is also made from S30V at the same as specified hardness to cut one foot sections of 1/8" ridged cardboard through a one inch section of blade on a draw. The cuts were made through the ridges to maximize wear. Both blades had primary edge grinds of approximately 10 degrees per side with secondary edge bevels of 20 degrees per side from the fine Sharpmaker rods. During the cutting the sharpness was determined by the force required to push cut light thread. The small Sebenza was also compared on cardboard to a K2 from Dozier in D2, to cut 1/4" ridged cardboard again through a once inch section of blade on a draw. Both blades again had secondary edge bevels of 20 degrees per side from the fine Sharpmaker rods and the sharpness was determined by the force required to push cut light thread.

Manix vs small Sebenza
cardboard Manix small Sebenza
(meters) force required to cut light thread
 0.0 89 (3) 76 (6)
19.9 216 (25) 231 (23)
42.4 333 (25) 367 (25)
K2 vs small Sebenza
cardboard small Sebenza K2
(meters) force to cut thread
 0.0 86 ( 7) 94 (14)
3.7 202 (12) 234 (12)
8.6 221 ( 4) 245 (21)

The above was an average of two runs for each comparison and in each case there is no significant difference in the initial sharpness or edge retention which isn't surprising as these are similar steels, high hardness, and high carbide volume steel. The comparison vs the Dozier would have seen benefit from an extended run and a couple of extra runs to reduce the variance as it looks like the D2 blade might be a little behind which would be expected as the carbide structure of D2 is very coarse and thus the edge stability is relatively low. The Sebenza was also compared to a Byrd Meadowlark in 8C13CrMoV on 1/8" cardboard using slices through a two centimeter section of edge with the sharpness tested on light thread again. The edge on the Sebenza had been reduced to about 5 degrees and the Meadowlark was set at about 7.5 degres. Both had microbevels set at 15 degrees with the fine Sharpmaker rods.

Meadowlark vs small Sebenza slicing on 1/8" cardboard with a 2 cm section of blade. Sharpness measured push cutting thread. Edge set at 15 degrees / sharpmaker fine.
cardboard small Sebenza Meadowlark
(meters) force to cut thread
 0.0 75 (7) 80 (8)
3.9 192 (12) 219 (15)
7.8 273 (22) 299 (24)
11.7 381 (37) 379 (27)
Meadowlark vs small Sebenza slicing 1/8" cardboard with a 2 cm section of blade. Sharpness measured slicing light cotton. Edges microbeveled at 20 degrees / fine sharpmaker
cardboard small Sebenza Meadowlark
(meters) edge length to cut cotton
 0.0  19 ( 4)  30 ( 8)
3.9  77 ( 12) 197 ( 24)
7.8 123 ( 19) 496 (104)
11.7  200 ( 25) 483 ( 90)

The above was an average of two runs and similar to before there was no significant difference in measured push cutting sharpness. However the Meadowlark.html was ripping the cardboard after the first four meters and thus it was determined that measuring push cutting sharpness was not a valid measurement of slicing edge retention so the cardboard cutting was repeated and this time the slicing aggression aspect of sharpness was measured by slicing light cotton. The results are shown in the table on the left. This time the edges were microbeveled at 20 degrees per side on the fine Sharpmaker rods. There is a large difference in slicing aggression through the cutting which is attributed to the increased wear resistance of S30V. This was given further confirmation as a few passes on a smooth steel the small Sebenza was again shaving sharp.

The small Sebenza was compared to a small custom fixed blade in D2 by Mel Sorg. Cuts were made on a slice through two centimeters of blade on 1/8", slicing aggression was measured by again cutting light cotton on a draw. Another comparision was made against a Temperance on similar stock with the sharpness measured by the same method but the blades having a microbevel of 20 degrees with the medium/sharpmaker rods :

D2 Sorg vs small Sebenza.
cardboard small Sebenza Mel Sorg custom
(meters) edge length to cut cotton
 0.0  26 ( 2)  21 ( 3)
1.5 49 (8) 43 (5)
4.5 73 (13) 69 ( 8)
10.5 100 (13) 118 (11)
22.5 198 (18) 191 (24)
Temperance vs small Sebenza
cardboard small Sebenza Temperance
(meters) length of edge to cut cotton
 0.0  25 ( 1)  29 ( 2)
1.5 54 (7) 69 (4)
4.5  80 (11) 116 (11)
10.5 108 (13) 226 ( 7)

No significant difference in slicing aggression for the first comparison, but the Sebenza showed a significant advantage over the Temperance which agrees with the CATRA work done by Spyderco on those two steels. To further confirm the performance vs the Temperance, another Temperance was used and the work repeated. The first run was with both blades with primary edges of 11 degrees per side, the cutting a draw through two centimeters of blade and the edge retention checked by slicing light cotton. The edges were set at 20 degrees with the fine Sharpmaker rods. For the second two runs were with the blades rehoned to 20 degree setting on the medium rods.

Temperance vs small Sebenza, 20 degree fine Sharpmaker microbevel.
cardboard small Sebenza Temperance
(meters) length of edge to cut cotton
 0.0  21 ( 2)  24 ( 3)
2.5 106 (11) 189 (26)
7.5 155 (18) 265 (25)
15.0 220 (25) 773 (26)
Temperance and small Sebenza : medium sharpmaker microbevel
cardboard small Sebenza Temperance
(meters) length of edge to cut cotton
 0.0  32 ( 2)  29 ( 4)
2.5  95 (14) 136 (12)
7.5 123 (18) 260 (30)
15.0 220 (30) 410 (78)

The Sebenza had a significant advantage in both runs but it was reduced with the more coarse finish which may be due simply to the wear of the micro-teeth being more dependent on hardness than carbide volume. In summary, for slicing cardboard, the Sebenza had no advantage in push cutting edge retention over a Spyderco Manix in S30V, a K2 in D2 and a Meadowlark in C13CrMoV. However for slicing cardboard the Sebenza had a significant advantage over a Meadowlark in C13CrMoV and two Temperances in VG-10 and matched the performance of a Mel Sorg custom in D2 .

Plywood : to examine the push cutting edge retention dependent on durability, the small Sebenza was compared to a Pacific Salt in H1, Calypso Jr in ZDP-189, and Meadowlark in C13CrMoV. on plywood with all blades have similar edge grinds of six degrees per side. The Sebenza took significantly more damage in comparison to the other two blades. Similar problems with the edge durability at low angles have been reported on Bladeforums.

Rust : The corrosion resistance of the small Sebenza was examined alongside a Rucksack, Calypso Jr in ZDP-189 and Meadowlark in C13CrMoV. The knives were subjected to a solution of one tbls each of; "Big Up" soda, vinegar, lemon juice and table salt in four cups of water. Each knife was freshly sharpened finishing with a micro-bevel set at 20 degrees by the medium Sharpmaker rods. The blades were wrapped with a piece of paper towel, dipped in the solution until saturated, then held to drain and all placed in a plastic container. Sixteen hours later the blades were used to cut some cardboard and the edge retention check on a slice by cutting light cotton under a 200 gram load, the cutting was stopped when the blades on average had about 10% of optimal sharpness. The results of four runs :

Edge retention of a small Sebenza, Rucksack, Meadowlark, and Calypso Jr. slicing 1/8" cardboard through a three centimeter section of blade and the sharpness checked by slicing light thread. Edge set at 20 degrees with medium Sharpmaker rods.
amount of cardboard Calypso Jr. small Sebenza Rucksack Meadowlark
(meters) length of edge to slice light cotton
 0.0 0.25 (1) 0.25 (2) 0.31 (2) 0.30 (2)
 5.9 1.4   (2) 1.2   (2) 1.2   (1) 1.2   (1)
17.2 2.2   (3) 1.7   (1) 2.5   (3) 2.2   (2)

After the first short round of about six meters, there was no significant difference in performance of any of the blades. After the much longer round of seventeen meters the Sebenza is cutting signficantly smoother in hand, but the variance is too high to allow a statement of statistical significance. The big problem was the random nature of the corrosion. Each of the blades had at least one run where the edge retention was very low and after cutting six meters was blunter than after cutting the seventeen meters on average. It mainly depended on where the rust formed because if it hit the edge then there was almost no edge retention as the entire edge could just crack off within the first few cuts.

To the right are some shots of the blade through the runs. Pictures for each run can be seen on PhotoBucket. Clearly the Rucksack has the highest corrosion resistance which would be expected given the composition of the steel which is a high chroimum/low carbide steel. The the small Sebenza is next followed by the Calypso Jr. and Meadowlark. Only the Meadowlark rusted in each run. The other blades all had one run where they showed only very light oxidization which didn't show up on a picture. Note the rust only formed on abrasion left by the 200 grit SiC stone which was used to set the edges. On the Sebenza and Calypso Jr. this is the secondary edge bevel, however on the Meadowlark and Rucksack this is actually the entire primary grind which is why it has a larger rust volume but the fraction or percentage of corroded area is similar to the Calypso Jr..

As an interesting example of how random deviations can skew results, one of the runs with the Calypso Jr had the rust forme along the edge removing the sharpened micro-bevel and there was essentially no fine cutting ability in that section of edge. Because of the high variance due to the random nature of corrosion it would seem that a lot of trials would need to be performed before a clear statement on superiority could be made between the high carbide steels but it was immediately obvious that the Rucksack was in another class in terms of corrosion resistance.

Ease of Sharpening

S30V is significantly harder to grind than common cutlery stainless like VG-10. The thin edge on the small Sebenza does compensate by minimizing the volume of material which needs to be removed. However there is a fairly obtuse secondary edge bevel at 20+ degrees which had to be removed before it could be honed on the Sharpmaker. Reducing the angle on one side to 20 on the corner of the medium rods took 1050 passes (yes, over a thousand). The other side took 150 passes with an x-coarse DMT hone. Sharpening the entire bevel was too time consuming so a micro bevel was added at 30 degrees per side by adjusting the height of the Sharpmaker on one side. After the Sebenza was used for awhile, the primary edge grind was taken down to 10 degrees per side with a 220 grit SiC hone. This was to both raise cutting ability as well as enhance ease of sharpening. The performance both before and after the modifications is noted in the following table :

new in box vs modified blade comparison on a small sebenza addressing sharpness and cutting ability on hemp and birch hardwood
condition Sharpness Hemp wood
thread push birch
NIB 125 (12) 22.5 (1.0) 5.6 (4)
modified  71 ( 4) 14.0 (1.1) 2.6 (1)

With the adjusted edge profile and resharpening, the performance of the Sebenza jumped up amost 2:1 on the thread, hemp and wood cutting, with the wood cutting showing a greater increase than the hemp which is to be expected as it is more sensitive to relief grinds. With the relief grind ease of sharpening of the Sebenza was very high. The reduced edge angle does lower edge durability but considering the deep hollow grind the very obtuse initial edge angle seems inconsistent as it would turn the primary grind into the weak point. The above plastic cutting was repeated with the new profile with no problems, again care was taken not to twist the blade. Later the the edge bevel was reduced to six degrees per side and later still the Sebenza was sharpened flat to the stone which set the primary edge at about three degrees per side which significantly effected the primary finish. Care needs to be taken to avoid grinding into the thumb stud at this angle. It was usually finish sharpened with a microbevel of 20 degrees which was about 0.1 to 0.2 millimeters wide. Later still the edge started fracturing on the Sharpmaker and would not sharpen similar to what was seen on a Benchmade Skirmish and RSK.

Lock

The small Sebenza has an integral lock, essentially a Walker liner lock which uses one of the handle slabs for the liner. The lockup was stable under light to moderate spine whacks which readily dented clear pine. White knuckling was not a problem outside of grips which ran the handle straight across the second joint of the index finger which would allow the lock to be released readily in a tight grip.

Testing the stability under torques was problematic because the edge was so thin that twisting the blade in hard materials would be likely to simply crack the primary grind thus it was examined in an artifical manner. The blade was worked into a crack on a piece of pressure treated 4x4 and the blade twisted to check for lock bar movement. Fairly high forces were needed to cause the blade to unlock and were mainly due to direct force across the lock bar with the fingers.

The twisting also only tends to unlock the blade when it is rotated in a counterclockwise direction, clockwise torques just close the lock tighter. This brings up a point of concern as it grates the lock bar across the end of the blade thus causing a lot of wear. After just a couple of months of carry and use, not even as primary EDC, the lock bar is more than 4/5 of the way across the face. This holds even when the Sebenza is taken apart and reassembled.

Handle

In a hammer grip the clip presents a high pressure point. In reverse grip the apex of the transition between the grind of the handle along the top where it forms the triangle at the front is rather sharp. A choked up grip with thumb on the spine however shows the use of the fully rounded spine. In such a grip with the right hand, which is common in cutting cardboard for example, the tip of the clip is abrasive against the back of the index finger. The inside of handle slabs could be more rounded however many folders leave that area almost perfectly squarish such as the Byrd Meadowlark whereas on the small Sebenza it is beveled just like the outside. The rather small handle on the small Sebenza also has issues with grips which place the handle inside the hand as this generates a high pressure point. The handle is most ergonomic in light pinch grips.

Comments and references

Comments can be emailed to cliffstamp[REMOVE]@cutleryscience.com or by posting in the following thread :

More information on the small Sebenza can be obtained at the Chris Reeves website. The pictures in the above are mainly from the PhotoBucket Sebenza album.


Last updated : 11 : 11 : 2006
Originally written: 05 : 05 : 2005
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