Just found this forum and Jerry's threads on Sharpening.

Wow Thanks!! Love it. Jerry's obviously been down the path before me and I sure appreciate him looking over his shoulder and egging me on.

BTW, I developed on an idea I saw on a japanese water stone I got from Japan. I can't read the directions, but I understood the picture. It involves using coins to set an EXACT angle on your knife. So I built a calculator:

http://knives.mylamb.com/calc.htm

Hope you find it useful.

Steve

Those plug in formulas are pretty cool! Thanks.

I have to admit though that my take on edges is somewhat different. The Japanese (and many other) woodworkers are fanatics on the precisely fixed edge bevel. That's probably because directional control of such tools as chisels is easier with a set edge. IMHO, ease and efficiency of cutting is not.

I recently did a bit of consulting with some American woodworkers who were interested in the potential of CPM-3V for plane blades as well as chisels. While on the subject I couldn't resist asserting my thoughts on the fixed bevel versus the convex edge. After a long pause in the discussion, they began to look at some tools from the shops of old woodworking masters who were known for their precise work. What they discovered were convex edges, the result of some not so precise hand sharpening on a stone that over time just naturally tended to round everything. Instead of cutting well because they were so sharp or because of some superior steel, they were likely cutting well because of the shape of the edge. It opened a few eyes, though I understand there were some roars of outrage from some of their more tradition-bound colleagues.

(BTW, they were studying these edges with photomicrography, so they had documented evidence of their conclusions.)

Here's my take in a nutshell. If you measure how sharp something is, not by seeing how well it pops hair off your arm or by polishing a precisely fixed bevel down to beyond 10,000 grit (the level attained by serious woodworkers), but by how well a blade actually cuts as measured by the "ease" with which it cuts, you will find that a convex edge has one very distinctive advantage. Because there is less induced drag from a convex edge compared with a fixed bevel, you can achieve the same cutting efficiency with a steeper final edge angle - probably as much as 5 degrees steeper. That in turn gives you a more robust edge as well as an edge that generally wears better. The increased wear is due to two factors. One, by elimination of microchipping, you eliminate one of the major causes of dulling. Two, because of the nature of the convex edge, the sides of the edge are working with the cutting edge, like a wedge, stretching the material being cut and thus making it easier to cut.

At the same time, because the convex edge allows only minimal contact with the material being cut when compared to a fixed flat bevel, you have less resistance to the cut. If you were to take those same bevels you've created with your stones, and simply knock off the shoulder of the bevel (rounding is best, but a secondary bevel is fine to demonstrate this) you will find the blade cuts far more efficiently in almost any medium.

That's my take anyway...

Jerry,

Thank you AGAIN!

Acutally I'm more in line with you on convex edges than it might appear.

My lastest attempts at sharp have involved using stones to set the edge angle. Obviously that's a flat edge. But I don't stop there.

As you point out, I don't think a 'perfectly' flat edge taken out to 10,000 grit is going to hold up for most knife work. So....

I then strop to a slight convex edge. Here's what's going on in my mind right now on the subject:

http://knives.mylamb.com/images/burr.gif

Developing the burr weakens the steel due to the bending back and forth (BTW I think the brass rod test itself weakens a fine edge, but I'll probably get shot for saying that.)

The larger the burr and the more flexing it is subjected to, the more the steel is weakened. When the burr comes off, not all the weak steel comes with it. So the final process of stropping not only creates a fine convex edge, but also removes the last (hopefully) of the plasticized steel.

I'm going to go out on a limb with your wood working fellows. Why is an edge taken out to 10,000 grit so much liked by the wood working crowd? Could it be because the burr created on a 320 stone is rather large and therefore weak. By working your way out to that grit it is not just the polish, but the process removes the weakened steel from previous stones and the fine grit doesn't not create more weakened steel. Possible?

Based on your information, looks like I'm on the right track with a secondary convex bevel improving edge retention.

The question, for me, is your information on increased cutting performance. Is a secondary convex bevel enough? How does that compare with a completely convex edge. What about edge thickness? What about the blade grind (convex, flat, hollow)?

Of course all this is based on the knife's purpose. The high performance knives I'm interested in (People please don't barf) are kitchen knives. If I can make an edge that will withstand that, I'm a maker!

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Sidebar: It strikes me funny that makers and users will talk about how many deer they can clean without sharpening and the wife can't finish making a pot of stew without using a sharpening steel.
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Steve

Besides being a knifemaker I'm also the cook around here and generally agree that a kitchen knife faces far more severe demands on it than almost any hunting knife. Some of the pig and moose crowd will argue that, but I don't have any experience with those critters. In the kitchen I use forged Henckels and a rough steel. It's fast and one go at the steel will usually get me through a meal or two. I always sharpen before tomatoes.

We are speaking of different secondary bevels. The one I was speaking of was at the top of the edge bevel, not at the edge itself. I also don't agree with your position that the edge steel is appreciably weakened by the sharpening process, so long as everything stays relatively cool. The photomicrographs of the CPM-3V chisels revealed no rounding over or microchipping of the edge at about 100X. The edge had been driven through knots in hardwoods (maple as I recall).

I think the point of going to 10,000 grit is to literally polish away the wire edge, leaving it clean. I take my edges to 1200-2000 grit, and polish off the wire with some Aluminum Oxide on a loose buff, done carefully. Some knifemakers sharpen with a belt, then use a hard arkansas to polish off the burr.

The polishing serves a second purpose and that is to reduce the drag induced by the edge bevel, basically making it more slippery.

To achieve what I am describing, assume in your diagram that those bevels are at 25 degrees. After they are fully formed, change the angle to 15 degrees and continue sharpening until the width of the edge bevel is half of where it started.

As for edge thickness, I think that's determined by the role of the knife. As far as the gind is concerned, I really don't think it matters. I have my opinions and will keep them to myself. :)