Question with a sebenza

[Robert Borowski]

I sharpened my micarta sebenza with s35vn the other day and ran into a problem with edge retention. I reprofiledthe edge at 18 degree per slide from 50 up to 0.6 microns. Whittled hair and sharp as a devils tongue haha, but then it stop slicing paper after like 10 cuts and it didn’t really slice paper well. I was pretty surprised and have a few theories but wanted to see what people with the WE and a sebenza have experienced.

I don’t want to do a convex edge but if that is the problem I could. Let me know if you guys have encountered the same problem and how you fixed it.

Thanks!!

[BassLake Dan]

..Let me know if you guys have encountered the same problem and how you fixed it. ..

Well Rib, looks like no one has had a crack at responding to you on this so i will give it a go… I wound up with 18deg per side a finish of 5u lapping paper after trying a zillioon stradigies. . I tried everything on the 35VN sebbie and this was the best I could do, as nothing much really works. The steel is not properly finished (in my humble opinion) at the Reeves shop… I have other S35VNs that I pocket EDC, for example a ZT0550, and it will take a -17deg with a finish of 0.3u (mirror) and even at that razor edge point sharpness it will out last the sebbie in EDC duty by 4x or better!

I am going to quote my neighbor, just up the road from Bass Lake, here in the Sierra Nevada Mountains, Mr Phil Wilson, who knows a thing or two about steel.. ” The best obtainable tool steel in the world will make the worst very expensive custom knife if the heat treating is not right.”

I recommend to anyone Phil’s fine site at this link

Don’t get me wrong, I love the Model 21 sebbie, carry it all the time, but the steel is just treated ‘soft’ and you will have to live with it or sell the knife.. Wish I had better news -Dan

[cbwx34]

I can’t speak to the steel quality, but an edge that fails after only a few paper slices means that it still has a burr. When converting a convex edge to a straight edge… it’s tricky reaching the very edge… if for example, you mark it with a sharpie, it may look like it’s all gone, but if you look at it under magnification, there can be the tiniest line still visible. There’s a video that talks about this…

My suggestion would be to start from around the 400g stone, thru to whatever you want to finish at, and make sure that you have a good clean edge established. If it still fails, then you could add a small microbevel at a higher angle (I’d do it with the ceramics or finest stone you have), just a few very light alternating strokes to ensure the edge is burr free, and strengthen it a bit.

Clay also did a video sharpening a Sebenza (but he returned it to a convex shape)…

There seems to be a lot of “problem sharpening Sebenza” threads and videos… switching a convex to a flat grind usually causes this. It doesn’t have anything to do with one grind being stronger or better than the other… it’s just a matter of getting to the very edge.

Let us know how it goes!

[Robert Borowski]

Thanks Dan, unfortunately this was one of my theories,I mean 58-59 RC is a little soft for me too. It’s also why I didn’t posted in on the CRK forum of the blade forums haha. Trust me a love CRK when it comes to quality but this isnt the first time I have experienced this so I thought I’ d post it to see if I was just doing something incorrectly. Seems like you speak from experience…have you owned a s30v CRK heat treated to their standard 58 to 59? Any better?

I have heard of guys who will heat treat a sebenza blade but I am not sure I want to do that with all my CRKs. Maybe a convex edge will do better. I did it with um umnumzaan and it’s held up a little better I think. .

[Robert Borowski]

I can’t speak to the steel quality, but an edge that fails after only a few paper slices means that it still has a burr. When converting a convex edge to a straight edge… it’s tricky reaching the very edge… if for example, you mark it with a sharpie, it may look like it’s all gone, but if you look at it under magnification, there can be the tiniest line still visible. There’s a video that talks about this…

My suggestion would be to start from around the 400g stone, thru to whatever you want to finish at, and make sure that you have a good clean edge established. If it still fails, then you could add a small microbevel at a higher angle (I’d do it with the ceramics or finest stone you have), just a few very light alternating strokes to ensure the edge is burr free, and strengthen it a bit.

Clay also did a video sharpening a Sebenza (but he returned it to a convex shape)…

There seems to be a lot of “problem sharpening Sebenza” threads and videos… switching a convex to a flat grind usually causes this. It doesn’t have anything to do with one grind being stronger or better than the other… it’s just a matter of getting to the very edge.

Let us know how it goes!

Thanks for the reply. Good thinking and I wish it was that easy. I don’t want to say I am a master with the wicked edge but I feel comfortable enough with it to be pretty sure I have made and the smoothed out the burr. I do the sharpie trick and more so I trust my finger to feel when the burr has been created. This one had the factory convex edge Which was uneven and not consistent so in re profiling I had to be sure I got a burr along the whole blade and checked it more than I typically do while going through the progression. Thanks for the reply I appreciate the brainstorming.

Yeah I might try the convex edge next. I have seen the vid and no did it on my zaan which did a little better I think. Its m y next step. I wi ll keep everyone posted for future references.

Thanks!

[cbwx34]

Cool. It sounds like you’re confident you’ve reached the edge, but an edge that fails that fast is still a burr issue. I would still try making a couple of very light, edge leading, alternating strokes with the ceramics (if you have them) at a 3-4 deg. higher angle. You’re not trying to create a microbevel… just enough to clean up the very edge… see if that helps.

If not, you can then go to Plan B. 🙂

[mike allen]

Well, I lost my sm Sebenza before I purchased my WES but I
never could get that knife to hold a good edge. It had s30v.
At the time I was using a tri- stone Norton.

Currently my EDC carry is the Spyderco Para 2 with the same steel.
This blade will not get dull. Go figure.

Above my PG.

[Cliff Stamp]

I don’t want to say I am a master with the wicked edge but I feel comfortable enough with it to be pretty sure I have made and the smoothed out the burr. I do the sharpie trick and more so I trust my finger to feel when the burr has been created.

To clarify, all edges will have a burr, the burr is simply the extent that the edge has not perfectly apexed. In general I doubt that you can see or feel a burr which is small enough to significantly impact edge retention because such a burr can be only for example 10 microns which is 1/100 of a mm, or 1/10 of of the thickness of standard paper. Yet even at that size it is on the order of 100 times the size it should be for a properly sharpened edge and thus the edge retention would be expected to be very low.

It can not be the hardness alone as the properties which effect edge retention (or in fact anything) are linear in small increments (everything is) so a change of 1-2 HRC can not alone make a dramatic difference. As well consider that a lot of makers/manufacturers use and even prefer much lower hardness levels, one of the most dramatic being Jerry Fisk, well respected smith who uses a hardness on his personal blades just about 50 HRC.

Based on experience with the Sebenza and other blades, you are likely experiencing poor performance from a number of issues the most likely one being that the edge was over heated in the initial grinding. I would suggest :

-make one pass right into the stones to grind a small flat along the edge which clearly reflects light
-apex the edge until it stops reflecting light
-increase the angle dramatically (as in 10-15 dps) and use 1-2 passes per side
-reset the angle and use 10-20 extremely light passes (5-10 grams of load) to remove the heavy micro-bevel

I would suggest going no further than a medium grit, something similar to the brown Spyderco Rods, a 600 DMT, fine India, etc. whatever the WE uses which is close to that. At this stage if the edge forms clean then it should :

-shave easily, just barely hitting the skin with no draw
-push cut newsprint almost on a full 90

If it can not do these, and you can get it to do it on another knife, and the edge was visually apexed (you can see it stops reflecting light) then is is almost always the case that the edge was severely burnt. You can then keep sharpening it hoping the problem with stop – or return it. As well if there is someone close by who can sharpen you can ask them to check to ensure it isn’t a technique problem as we are inherently irrational by nature and can be extremely biased even when we think we are not.

[BassLake Dan]

.. I have other S35VNs that I pocket EDC, for example a ZT0550, and it will take a -17deg with a finish of 0.3u (mirror) and even at that razor edge point sharpness it will out last the sebbie in EDC duty by 4x or better! ..

since I stated the above, it seemed like a good idea if I could ‘test” my empirical observation about different knife makers results with that steel. Today I sharpened my sebbie with my usual routine for that knife (19deg with a finish of 5u) then put it on a knife test jig to measure a sample of push cuts. Usually the data is collected on this jig across equal distant points across the total blade length. But for this test I repeatedly re-set the jig to land on the same approximate area every 5 test stokes. The idea on that is that the testing, is by nature, semi destructive to the apex edge as the jig contacts the same area repeatedly. Perhaps this would give a clue about what seems to be a “soft” steel on the sebbie. I will repeat this test tomorrow with a ZT0550 which is the same steel, but is much more durable in EDC use.

FYI, the sebbie turned in a very solid performance here, and although after 75 contacts the push cut force went up abt 100 grams, I consider that very good. For your reference you can see that the sebbie started the test sequence in the area at about and just above 200 grams. That is a very sharp knife for EDC use, as a commercial razor blade will test out at about 120 grams to start.

I make one conclusion so far about all this: 1.) I think we might have debunked here the ‘must be operator error and you have a wire hair remaining on the blade apex’ issue.. I conclude that the thing would have never survived 75 contacts in the same area and only shown a 100 gram increase if there were serious apex issues with sharpening technique. It seems likely that things would have degraded much more rapidly and the push cut forces would have ramped up to much higher values much sooner if that was the case

Keep in mind: It is important to note that push cut apex testing reveals only very limited information about real world “cutting ability”.. No matter what the results of my testing tomorrow of the ZT0550 I stand by my statement that the ZT holds up 4x better than a sebbie in the real world.

(Warning!) Anecdotal irrelevancies follow: a.) There are many reports of owners returning a sebbie to ‘the factory’ for resharmening, only to find to their horror that the blade has been run through a commercial fast cutting jig and suffered as much as a 2mm ‘shave away’ of blade length/ and height. b.) Chris Reeve has been quoted as saying ‘ I like to keep the blades soft so the are ‘easy to sharpen” d.) the knives are know to be a so-called mid-tech product, a term which is widely accepted to mean ‘out-source critical components’, in this case steel hardening, tempering, and so forth. e.) I personally micro graphed my sebbie on arrival (out of box) and noted one of the most crappy factory applied sharpening jobs I have ever seen on a +$300 edge. The edge angles and depth were all over the ball-park and the grit looked about-300 incompetently applied from a wheel that was obviously in need of immediate maintenance

link to raw data here..

link to raw data here..

[cbwx34]

Based on experience with the Sebenza and other blades, you are likely experiencing poor performance from a number of issues the most likely one being that the edge was over heated in the initial grinding. I would suggest :

-make one pass right into the stones to grind a small flat along the edge which clearly reflects light
-apex the edge until it stops reflecting light
-increase the angle dramatically (as in 10-15 dps) and use 1-2 passes per side
-reset the angle and use 10-20 extremely light passes (5-10 grams of load) to remove the heavy micro-bevel

This is a good suggestion.

[cbwx34]

I make one conclusion so far about all this: 1.) I think we might have debunked here the ‘must be operator error and you have a wire hair remaining on the blade apex’ issue.. I conclude that the thing would have never survived 75 contacts in the same area and only shown a 100 gram increase if there were serious apex issues with sharpening technique. It seems likely that things would have degraded much more rapidly and the push cut forces would have ramped up to much higher values much sooner if that was the case

Good post and testing… but I’m not sure I understand (or if you’re saying…) how you came to this conclusion for Rlb’s knife? I think it would also be benefical if, after the testing you just did (if you haven’t done anything else to the knife), is to repeat what Rlb did… make 10 cuts thru some paper and see how the edge holds up.

[BassLake Dan]

..but I’m not sure I understand (or if you’re saying…) how you came to this conclusion for Rlb’s knife? I think it would also be benefical if, after the testing you just did (if you haven’t done anything else to the knife), is to repeat what Rlb did… make 10 cuts thru some paper and see how the edge holds up.

The answer is because Ribs knife is a member of a set.

Well, it’s the old problem: If you don’t ask the right question you will get the wrong answer every time. In this case you have phrased the question (and it looks like maybe Cliff did as well..) to inquire specifically about a single member of and one occurrence in a subset of a much larger set. By phrasing any question that way it forces the answer to include the member of the subset to then become part of the answers equation. The question, properly phrased in relation to the largest set of which all are members of is: “Why are there so many reports of issues with the CRK sebenza failing to properly hold or take an edge that is equivalent to other similar knives made with the same steel?” If you ask the question like this “Why did Joe or John or Harry have trouble with the CRK sebenza failing to properly hold or take an edge that is equivalent to other similar knives made with the same steel?” then, of course Joe, John and Harry become part of the answer, when in fact they are not.

Forensic science battles with this all the time, all science does in fact. In this brief topic thread you have 3 separate reports (the Joe John and Harry’s of this case..) of trouble with the knife in question. If you look at the larger sets as seen on, for example, Blade Forums, Knife Forums, etc you will see hundreds of trouble reports that comprise a very large set group..

Anyway, I did as you requested, I cut 10 slices of copy paper with the sebbie, and then it began to fail to direct push cut at 90. I put it on the test jig and took a sampling of points across the blade and the numbers have jumped to 350-375 grams from un disturbed locations that were in the low to mid 200s. I will repeat all this on the ZT0550 as soon as I get a chance, hopefully that will be today, but only so many hours in the day for me 🙁 .

[Cliff Stamp]

The question, properly phrased in relation to …

As an aside, that was a very nice description of the problem, very elegantly worded.

In regards to performance, one thing to keep in mind is that however Reeve is hardening the steel, S30V / S35VN etc. the difference in performance can not be that dramatic. If you look at edge retention by heavy abrasion (CATRA) or micro-loading to measure sensitivity to roll/chipping, then it takes something major to make a multiple factor.

For example Leatherman’s 154CM compared to AISI420 which is a dramatic difference in both hardness (likely 5+ points) and carbide volume difference of > 15% only produces a 3X difference in edge retention and in order to even get this you have to go to extremes and wear the edge down to under 10% of initial sharpness (blunting is nonlinear so the further you go the larger the gap you will see between steels).

As strength would be linear with hardness, a 1-2 point change in hardness could produce at most < 5% of a difference in strength. Now if Reeve is leaving large amounts of retained austenite in the steel there could be a more significant effect, but again I can't see how you could even get a 100% difference due to that as you are talking about maybe a 10-15% compositional change at maximum.

One thing to be really careful about is how perceptive bias will influence people. It only takes a very small amount of people to suddenly create the idea that there is a problem, people will then mob to that like sheep and see a problem when none exists. Unless you have people actually doing blind runs, which few people do – be very very careful as Elmer Fudd notes.

Again to clarify, I am not saying I agree with Reeves decision being optimal and I have said as much on his forum – but I can't see it being that dramatic of a difference either. This is physics after all and all of these properties have bounds on them. You can't take S35VN and drop the hardness point by one and all of a sudden it is acting completely different. Note that the difference between for example Reeve and Spyderco is likely smaller than the difference in either of their knives in-batch. It is common to see HT notes claim 1-3 HRC as the goal because the batch tolerances, thermocouple tolerances, etc. . all can easily produce a difference of that size.

All of that said, I would be interested in your results. By the way it is pretty simple to add a regression line to the results of the tape and then a simple t-test to check if the force statistically changed within a significance tolerance. If you send me the XLS sheet I can add that.

[cbwx34]

..but I’m not sure I understand (or if you’re saying…) how you came to this conclusion for Rlb’s knife? I think it would also be benefical if, after the testing you just did (if you haven’t done anything else to the knife), is to repeat what Rlb did… make 10 cuts thru some paper and see how the edge holds up.

The answer is because Ribs knife is a member of a set.

Well, it’s the old problem: If you don’t ask the right question you will get the wrong answer every time. In this case you have phrased the question (and it looks like maybe Cliff did as well..) to inquire specifically about a single member of and one occurrence in a subset of a much larger set. By phrasing any question that way it forces the answer to include the member of the subset to then become part of the answers equation. The question, properly phrased in relation to the largest set of which all are members of is: “Why are there so many reports of issues with the CRK sebenza failing to properly hold or take an edge that is equivalent to other similar knives made with the same steel?” If you ask the question like this “Why did Joe or John or Harry have trouble with the CRK sebenza failing to properly hold or take an edge that is equivalent to other similar knives made with the same steel?” then, of course Joe, John and Harry become part of the answer, when in fact they are not.

Forensic science battles with this all the time, all science does in fact. In this brief topic thread you have 3 separate reports (the Joe John and Harry’s of this case..) of trouble with the knife in question. If you look at the larger sets as seen on, for example, Blade Forums, Knife Forums, etc you will see hundreds of trouble reports that comprise a very large set group..

Anyway, I did as you requested, I cut 10 slices of copy paper with the sebbie, and then it began to fail to direct push cut at 90. I put it on the test jig and took a sampling of points across the blade and the numbers have jumped to 350-375 grams from un disturbed locations that were in the low to mid 200s. I will repeat all this on the ZT0550 as soon as I get a chance, hopefully that will be today, but only so many hours in the day for me 🙁 .[/quote]

Makes sense… although I’m not so sure that the conclusion can be so quickly made. But I see where you’re coming from.

Thanks for doing the cut test… at least that relates some to Rlbs knife. This will all be even more beneficial when your tester becomes more widely used, and some of your findings can be correlated to other factors… for example right now saying a blade “failed to cut” could mean a number of things, but having an actual number would certainly narrow things down. I like where you’re headed with that.

[BassLake Dan]

…
As strength would be linear with hardness, a 1-2 point change in hardness could produce at most < 5% of a difference in strength…..

Well, darn the luck I just got home very late and did not get to the ZT testing, but will for sure do it and post results tomorrow..

I know very little about steel from a material science point of view, but do I understand what you are saying here?

Is your use of the term "strength" the same term I am thinking of in this discussion here, my term is more like: "wear resistance in normal use" (wear resistance to me would include a range of factors including deformation or plasticity if the blade edge was side cut or 'torqued' against a load, abrasion resistance to hard materials, etc etc..) anyway my question is what you are saying is that wear resistance is liner related to the RC hardness scale?

I thought the effect was more logarithmic and therefore the factor becomes very significant across the range of say: 56RC to 61RC. I did not pick those numbers out of the air, as Reeve states that when they began the use of Crucible steels at their shop (around 2002 ?) they chose 56, in sharp contrast to Phil Wilson who was working with Crucible and responsible for a lot of the development and stated optimal RC to be targeted to 61. So there is a big range there. Is it just linear, is that correct? If I have a 56RC then I have to make it test RC 112 to double its wear resistance??

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