Edge geometry and RC

B

babtron

Joined
Jan 5, 2015
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Hey guys, I've had my small Sebenza 21 since March or so 2013. I love the little guy. I carried it for quite a bit in 2013 but moved on to carrying other knives. Well, now I'm back to carrying this beauty.

I was carrying a lot of Spydercos with FFG blades. They were insanely sharp and I was able to get them insanely sharp as well. With my Sebenza, I'm able to get it to cut phone book paper and shave with somewhat relative ease, but they don't feel as sharp as say my SB Df2 or ZDP D4. I know my technique isn't the best, but it isn't horrible either. I'm able to get pretty damn good edges on my knives. Is this due to this geometry of the blades on the Sebenza? Is the Sebenza by nature, not as thin as the FFG Spyderco uses?

Also. I noticed, that light reflects off the apex on my Sebenza after extremely light use, mainly just cutting paper. It is still sharp, don't get me wrong. The edge catches on my nail, cuts phone book paper and shaves. It's just something I noticed--but never noticed it with say, ZDP-189. Is this due to S35VN not being that hard and the hardness is lower?

Absolutely love my SM Sebenza. I'm saving up for a Insigno :D

*yes, yes I am noob. Take it easy please*
 
I'll be curious to see the replies as well. It also seems to me that I'm not able to get my small Sebbies as sharp as my Native. They're plenty sharp so it's no biggee. Just not the razor edge I usually end up with on the Native, or even my SAK - but I know the steel doesn't compare on the SAK. I wondered too if it's the blade grind.

I use the sharpmaker at 40 degrees inclusive on everything.

And I'm not a heavy duty user. Just cardboard and typical day to day junk that truthfully could be done as well with my SAK, but I appreciate nice knives of all types.
 
I have a bit of experience when it comes to honing, and have collected Spydercos for years. If anything, the modern Spydercos are thicker behind the edge than most CRKs I have played with. I have reground a few Spydercos to get them as thin.

That said, there are some striking differences between the brands that may lead to your observations. First and foremost, ZDP-189 is extremely fine grained and most of the examples I have from Spyderco are well north of 63Rc. I am not hip to your nomenclature for the other knife...perhaps a DragonFly? Is it VG-10? If so, that is a PHENOMENAL steel in my opinion. Spyderco's VG-10 is very fine grained and exceptionally easy to sharpen in the right hands. I find that alloy to more readily support a show edge (one that performs all the parlor tricks like hanging hair cleaving) with the lowest honing effort.

Conversely, the CRK utilizes an equally wonderful steel, but it behaves very differently. It relys on a softer matrix that supports vanadium carbides. One way I describe this to new honers is imagine a candle formed with shards of glass in it. If the wax is really hard, you can shape it into an edge, but if the wax is a little soft it will allow the shards to be exposed at the surface more easily and they will allow the candle to cut FAR longer (and aggressively) than if it were simply hard wax doing the duty (and as you might imagine, regardless of how hard you try, that wax is softer than the glass...so at higher hardness, the wax will simply chip away and expose the glass anyway). That is pretty low tech and not a 100% accurate annalogy, but hopefully it helps.

To be sure, CRK heat treats the steel really well and refines the grain size a LOT, but the nature of the alloy (in my opinion) is that it always will behave like a coarser grained product. It is no wonder to me why Chris developed his heat treat this way.

For years I marvled at miror edges and lamented vanadium rich steels for their inability to support a supper fine edge...then I realized these steels were made for work and not show. You can polish them just fine, but the effort is in vein because the edge will stabilize quickly (as you see) to a "working" level of sharpness...and that level of sharp will generally outlive other common blade alloys if you really push it while working.

Or said another way, if you demand an edge that treetops hair and want to maintain it at that level, it is the wrong steel and hardness combination for you;)

Hope this helps.

I doubt there is anything wrong with your blade. If you have calipers, measure it. I think you will find it is prettty thing behind the bevel;)
 
rishma said:
^quite a good analogy to visualize the burr.
Click to expand...

Thank you, but I am assuming that there is no burr. For any steel/alloy to perform well, the burr must be removed before the sharpening/honing process can be considered complete.

However, this does lead me to another point I will make about vanadium rich steels...MANY people will form a burr, then remove it, then polish the bevels to a mirror shine. While this is pretty, the actual apex is quitte un-refined in this example. They quite litterally form a burr, tear it off (leaving a jagged agressive edge on a micro-level) then polish the bevels behind this (much coarser) apex.

The irony is, these edges will perform nicely because the carbides in the steel are doing exactly what they were put there to do...but it is really an example of an aesthetic bevel that is all show, with less "go". This is one reason CRK recommends a micro bevel to finish...because you are essentially honing the apex only...and that is really an important concept;)
 
Great job there unit.
I always finish with a micro burr as well.
That said every CRK that I have re-profiled for one of you guys or my own, was from a factory concave edge. Like unit said the thickness behind the edge is far thinner than you may think. But the factory edge is a little steep in my opinion and I like to make it flat as possible at 30 and then 40 for the micro.
The only issue that I have really dealt with on my own 21 and many I have sharpened is the thicker grind near the tip. The edge seems to always be a little steeper at that last 3/4 of an inch and it can take some practice or a re-profile of the angle to make sharpening easier in the future. They do this to make the tip stronger which is a huge benefit.
Practice makes perfect.
 
So Unit & Bella - those are excellent replies, and in an attempt to dumb it down so I'm sure I'm getting it, perhaps I'm expecting too fine an edge? A good working edge is both more desirable and easier to maintain?

As I mentioned, I'm getting them sharp, but maybe not as sharp as the CPM110v on the Spydie Native. Kind of a perception thing. I mostly just write this off to my inconsistent sharpening skills with my Sharpmaker, and the differences in the steel type and RC.

And yes, I realize I'm a goof if I can't even be consistant with a fixed angle Sharpmaker. But I have fun anyway. Lol.
 
Maybe unit can chime in with the scientific explanation. Im more a hands on kind of guy and have trouble explaining these things.
Honestly the first thing I did when I got me new sebbie a few weeks ago was simply take that factory edge and I threw a quick 40 micro on it with my white flats on the SM. Then I gave it a little time on the strop, black rouge to the green.
I was able to achieve a super fine edge and keep it maintained with the strop. So while I think it may be more difficult , it is possible to get a super fine hair splitting edge. It just takes getting a feel with this steel.
I think the reason that I was able to do this and will continue to do so would be. I do not continue and achieve a massive burr. I slow down just as I feel it forming and prevent having a "longer" burr on my edge. If you do, the edge with fold over in spots and will slowly remove by stropping and use. Or like we mentioned do a little extra work with the micro bevel. That is the best way to work this steel. Try to set a primary bevel between 30-34 and finish with the 40 micro to finish up before the strop.
But like he said, that will go away and leave a working edge which holds longer.
Sorry, im trying to check in while at home alone with crazy kids today.
 
Joe58 said:
So Unit & Bella - those are excellent replies, and in an attempt to dumb it down so I'm sure I'm getting it, perhaps I'm expecting too fine an edge? A good working edge is both more desirable and easier to maintain?

As I mentioned, I'm getting them sharp, but maybe not as sharp as the CPM110v on the Spydie Native. Kind of a perception thing. I mostly just write this off to my inconsistent sharpening skills with my Sharpmaker, and the differences in the steel type and RC.

And yes, I realize I'm a goof if I can't even be consistant with a fixed angle Sharpmaker. But I have fun anyway. Lol.
Click to expand...

There are a few concepts to consider.

What and WHEN is sharp?

First, what are you using as a defining "test" for sharp?
Second, when are you doing it...or when is a passing test MOST important to you?

Simply put, if you are good enough at honing, almost any steel can be made to pass most parlor tricks for "sharp" (splitting hair, cleanly shaving dry arm hair, push cutting phone books, the list goes on) fresh off the hones. Getting them to do it after a day of my typical use...none can do it consistently (depending on the trick("test") you select.

Once we explore these concepts, it is possible to assess the "problem". Is it the steel, the hardness, the geometry, your ability to hone it, or is it just a bad fit of expectations to what Chris intends for his knives?

You mention you can not get the CRK as sharp. If I can interpret this to mean, fresh off the hones, then I'd suggest the problem is with your ability to masterfully hone this steel...but id also suggest that these things don't need to perform tricks, just get it sharp enough to do what a pocket knife should do, and put the hones away...for quite a while;)
 
Thanks guys - your explanations were very helpful. I think perhaps I was seeing a problem where there isn't one.

I shall go forth and enjoy my knives. :)
 
Fantastic!

I would suggest that there is nothing wrong with pursuing the most insanely sharp edge you can produce in the name of furthering your abilities...but as one who has gone deep into that hole, I'll also suggest that there is a day of enlightenment that is bittersweet (often marked with the realization that some carry an INSANELY sharp knife that ironically they hesitate or outright refuse to use because they don't want to dull the edge).

Sounds silly, but it's true;)
 
I think we'd have to know how the OP is sharpening the knives. ZDP-189 is going to be much harder than CRK's S35VN. And Spyderco uses a V edge, while CRK uses a convex edge.

It could be that the OP is not reaching the apex of the Sebenza's convex edge, leaving it a bit dull. Or the soft steel of the Sebenza could be forming a burr that isn't entirely removed. And ZDP-189 is going to hold an edge a lot better, even if the edges come off with the same geometry.

My own Sebenza ran an edge-shoulder width more acute than any of my Spydercos.
 
Correct on the edge shoulder observation. Even more so toward the tip. I did not think about that so much.
I will eventually bring mine back to about 30. I have been impressed so far with my micro bevel. About 12 days of use and a strop session. Still about the same. A a few cardboard boxes and wood. Mostly packaging and food prep.
I never really had an issue sharpening any steel. Only one that gave me grief the first time was Elmax.

For basic touch ups and maintenance. I use the SM. Everything up to that is Diamonds and some 400 grit paper after that for re-profile work.
But the strop work at the end is the key to my success. That is always the final touch. The strop was more practice last year than any stones ever were.
 
Twindog said:
I think we'd have to know how the OP is sharpening the knives. ZDP-189 is going to be much harder than CRK's S35VN. And Spyderco uses a V edge, while CRK uses a convex edge.

It could be that the OP is not reaching the apex of the Sebenza's convex edge, leaving it a bit dull. Or the soft steel of the Sebenza could be forming a burr that isn't entirely removed. And ZDP-189 is going to hold an edge a lot better, even if the edges come off with the same geometry.

My own Sebenza ran an edge-shoulder width more acute than any of my Spydercos.
Click to expand...

Great points.

It would be a much shorter discussion for me to list the similarities I have noted while sharpening Spyderco's ZDP-189 and CRKs S35Vn (than the differences). Those two are so different, its almost funny.

The knife edge is such a simple concept that it tricks a lot of people into a corner when it comes to sharpening.

Some general concepts usually help though. Mark that edge, use magnification, LOOK at what you are actually doing. Do not fear a wider angle or the micro bevel. Pressure is usually a bad thing.
 
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