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TOPIC: Question with a sebenza

Re: Question with a sebenza 1 year 11 months ago #4110

  • mikeallen
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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.
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Re: Question with a sebenza 1 year 11 months ago #4301

  • CliffStamp
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Rlb wrote:
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.
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Re: Question with a sebenza 1 year 11 months ago #4302

  • BassLakeDan
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BassLakeDan wrote:
.. 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..

Last Edit: 1 year 11 months ago by BassLakeDan.
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Re: Question with a sebenza 1 year 11 months ago #4305

  • cbwx34
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CliffStamp wrote:
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.
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Re: Question with a sebenza 1 year 11 months ago #4306

  • cbwx34
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BassLakeDan wrote:
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.
Last Edit: 1 year 11 months ago by cbwx34.
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Re: Question with a sebenza 1 year 11 months ago #4309

  • BassLakeDan
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cbwx34 wrote:
..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 :( .
Last Edit: 1 year 11 months ago by BassLakeDan.
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