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 Post subject: Sharpening Cowry-X
PostPosted: Wed May 29, 2013 11:53 pm 
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Joined: Tue Apr 23, 2013 5:29 pm
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Location: San Francisco
I've got a couple knives from, as I recall, Kap-Kam in Kappabashi that I was told were Cowry-X. I don't have any reason to doubt that and I suspect that they are "house brand" knives made by Hattori in the early 2000s when I bought them. They are beautiful knives, but I can't seem to get the edge on them that I expect. I don't have any issues getting an edge that I like on my Japanese high-carbon steel.

I sharpen my knives with Shapton Glass Stones, usually the 2k followed by the 6k (US formulation). I was taught to only use trailing strokes, though I see in some of the videos here that some of the people use both directions. The edge coming off the 2k looks uniform to me. I get a nice polish on the edge with the 6k and can't see any significant imperfections, at least under 6x magnification. The "Sharpie trick" doesn't suggest that I'm missing spots on either stone. The knife is convex ground and I have been following the shop grind, which was excellent when I got them.

Any suggestions as to how to diagnose what I am missing on getting the edge to the quality that I can get on my high-carbon knives?

Part of me is tempted by Snow White, but I know that there has to be something I'm not getting right and succumbing to SAD isn't going to magically change that.


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 Post subject: Re: Sharpening Cowry-X
PostPosted: Thu May 30, 2013 1:06 am 

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It's a high carbon high Chrome steel so it will have lots of Chromium carbides. Think ZDP-189


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 Post subject: Re: Sharpening Cowry-X
PostPosted: Thu May 30, 2013 11:08 am 
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I strongly suspect technique - or the steel being something other than Cowry-x. I can remember seeing these knives in those stores. I suspect they are not Hattori made so the differences might be heat treatment too.

Cowry-x will take very acute angles. On a Cowry-x Hattori KD, I have gone down to 5 degrees per side. At this angle it is too delicate for all but the most gentle use, so I'd suggest 10 degrees as a conservative angle on this steel - per side, which is still very acute. Jason's right in that it is similar to zdp-189. At 5 degrees, it is hard for some sharpeners to distinguish between a very delicate edge and a wire edge and have reported that it won't hold up against lateral stress with a leather belt on a belt grinder - a truly stupid test for determining wire edges, suggesting that the originator of this test hasn't a clue. But I digress...

Technique-wise, go back to the 2k. Go for a flatter grind, but use your sharpie and view under more than 6x magnification. I suspect you are not hitting the edge of the edge - just damn close. If you need to convince yourself generate a small burr to be sure and then abrade it off. It should be quite sharp at 2k. If not solve your problems at 2k before going on to 6k.

You can use both trailing and leading strokes.

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Ken



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 Post subject: Re: Sharpening Cowry-X
PostPosted: Thu May 30, 2013 1:11 pm 
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In nearly every instance where someone can get "X" knife sharp as sin, but can't get "Y" knife same sharpness AND we're dealing with a high alloy steel in knife "Y" and not in "X"....it's a burr, wire edge, or poor heat treatment issue...or a combination of those.

What knives are you able to sharpen very well?

It's not an issue with your stones. Not at all.



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 Post subject: Re: Sharpening Cowry-X
PostPosted: Sun Jun 02, 2013 2:12 pm 
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Number one problem I see here is using edge trailing strokes on a powdered metal. You are inducing carbide-fallout while sharpening by doing too many edge trailing strokes. Try using edge-leading strokes and see how your results are then.



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Shaun Fernandez

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 Post subject: Re: Sharpening Cowry-X
PostPosted: Sun Jun 02, 2013 4:22 pm 

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I'd love to see some proof of that.


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 Post subject: Re: Sharpening Cowry-X
PostPosted: Sun Jun 02, 2013 5:16 pm 
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There is no way of inducing any significant carbide fall-out with edge trailing strokes....

Come on dude......????



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 Post subject: Re: Sharpening Cowry-X
PostPosted: Sun Jun 02, 2013 5:40 pm 
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I simply asked him to try a different method, that's all. Geeezzz...

Suppose you've never heard of "cooking" and edge, huh?

And yes, powdered metals, especially first generation ones, suffer from carbide fallout.

Edge trailing motions, by nature, are going to pull carbides out of the edge instead of pushing them in, simple physics. There is a certain point where you either stop or move on to a higher grit.

And it could be heat treat. and it could be technique. Not properly treated, a high-chromium metal will produce huge carbides, regardless if it was powdered to begin with or not.

This is also why fine grained carbon steel comes back so much better with stropping; less to fallout from finer grain due to less chromium.

We're all still waiting for a reply. lol

Guess I'll just keep my opinion to myself around you two. :(



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Shaun Fernandez

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 Post subject: Re: Sharpening Cowry-X
PostPosted: Sun Jun 02, 2013 6:09 pm 
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Not meaning to pile on Shaun, and I've had some strange theories too, but I'm not quite buying this simple physics. The pushing and pulling isn't pushing carbides in or out as the forces exerted are not perpendicular to the surface but rather more parallel so equally likely to dislodge carbides in either direction.

Shaun, do you have some references regarding 1st gen powdered steels and carbide fallout and fine grain carbon ...chromium.? Always here to learn.

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 Post subject: Re: Sharpening Cowry-X
PostPosted: Sun Jun 02, 2013 6:27 pm 

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I've been sharpening PM steels for a long time, carbide tear out and fall out are nothing but theories and wild ones at that.

The exposure of carbides as the matrix wears during cutting allows for that forever lasting working edge, but sharpening does not produce the same result.

I can see how these types of thoughts evolve though, mainly it stems from using a stone not able to properly abraid the steel as a whole. Not so noticeable at low grits but as you get to finer levels the hardness of the carbide becomes too much for most all waterstones to handle.

Using diamond hones on PM steels correct all these sharpening problems, I sharpened a few blazens last week and guess what I used?


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