The truth about sharpening

That's correct, the Razor Edge book describes the secondary bevel as the relief, and the primary as the bevel that meets the edge (I'll call it the edge bevel). Sounds like it is backwards from what most folks use.

Juranitch also recommends re-grinding the relief EVERY time you sharpen the knife, then slightly increasing the angle to put the "primary edge bevel" on. This seems like a whole lot of unnecessary stock removal to me. He is concerned with keeping the relief very thin for good cutting, but if you keep the "edge bevel" the same every time you sharpen, I don't see why this would be necessary.

He has drawings in his book showing how a wider relief adversely affects the edge, but in his drawings, as the relief gets wider, the "edge bevel" gets more and more obtuse, so it seems misleading to me... If the sharpening angle on the edge is held constant, it seems that the relief would take care of itself.

Again, I wish I could draw that here...
 
Swede7

Let's say that you are using a sharpening system such as an Edgepro. If you lay down a 30 degree (total) bevel on the edge, why worry about the secondary angle/bevel? 30 degrees is 30 degrees.


Think of it this way, if you took a piece of metal stock that was an inch thick, and put a 30 degree total edge on it, the results would not be equal to a 1/8 inch stock with the same edge on it. The reason for this is that the thickness behind the edge is different and proportional to the other piece of stock. 1/4 inch behind the edge of the one inch piece of stock is going to be a good deal thicker than 1/4 inch behind the edge of the 1/8 inch stock, which means that there is going to be more metal when you get to the edge, resulting in a duller edge than the 1/8 inch stock. Using a secondary edge is necessary when you have ground the relief as thin as they reccommend. IF you put a relief on the knife like they feel is excellent, and went straight to the primary edge, it would not last very long. Hope this helps.
 
Thanks Carl, I think I see what you mean. This is one topic where I wish we were all in the same room with a blackboard!

I agree with Jeff, sharpening is a fascinating subject!
 
I just want to say that this is one of the most intelligent and well written threads that this forum has seen in quite sometime. Its to bad most of the other posts couldn't be this informative.
Bob
 
Indeed, I agree. The forums are primarily for the rational discussion about knives. This thread is fan-damn-tastic!

Carl's last thread is SPOT ON! I was thinkign about this last night and I was going to post the very same thing. Thanks for saving me the effort Carl!

Carl's post in short: If you take a piece of 1/4" flat stock and put a 20 degree edge on it, it won't cut worth a damn! As you sharpen, though the primary bevel angle is the same (and by primary I mean the grind that takes the maker all of the tiem and effort to put on the knife!), the steel BEHIND the edge gets thicker. Too thick and your cutting performance goes down.

Read the "thin cuts better" thread going on right now! It is a very related subject.

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"Come What May..."
 
Am a bit confused here.

As I've posted before, I don't actually use knives all that much. Extremely sedentary lifestyle necessary due to health probs. As a result, I don't do much knife sharpening, and would consider myself the farthest thing from an expert.

I guess one tends to look closest to home. My Dad -- now 82 -- has had the little 2 3/4" bladed knife he carries almost 30 years. I've always thought he maybe oversharpened his knives, because he keeps a very good edge on them. I admit that the original blade shape is a bit obscure now, but the knife does all he needs. This is only the second pocketknife he's had in my recollection. The first one lasted more than 30 years. Both are/were carbon steel knives.

We're talking blades under a half inch from spine to edge to begin with. I believe he sharpens it weekly. So how come he still has blade left? At the rate some folks are talking sharpening here, a 2" wide bladed knife would simply disappear in a few years, I think.

Just what it is folks are doing with their knives to be at the point where they need to be re-profiled every time one sharpens? I can't help but think that a primary reason for writing books is to sell books, not necessarily to pass along knowledge, or significant info.

I really don't understand.

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Asi es la vida

Bugs
 
Bugs, my theory is as follows:

1st knife, kept for thirty years

2nd knife, kept for thirty years

Sharpens his knife weekly

52 X 60= 3120, your father has sharpened his knives around 3000 times, which means that he has had experience and knows how much to grind. He also might steel or strop his edge, but just might refer to it as "sharpening." When dealing with a knife blade under three inches, heaving chopping and other tasks that prove abusive to the edge cannot be effectively accomplished, so most tasks performed are not as harsh as, say, chopping down hardwoods. When Not2sharp wrote the post, I think he was referring to knives that see heavy use of all kinds over a long period of time. Hope this helps. I would also like to say that this post has had some very refined and informative responses.
 
Good points all around.

Differential tempering and multiple blade grinds are less of a problem with traditional folders. I have seen quite a number of older knives that have had the blades used and sharpened down to about toothpick size. I have also seen basic utility kitchen knives worn down from chef knives to fillet knives in a matter of months (I once owned a very good steakhouse).

My concern though is with some of the higher performance knives. When we look at knives that have been differentially treated, with pronounced primary and secondary edge bevels, heavy blade coats, or special edge grinds; they are going to perform better, but they are going to be harder to maintain, and at some point putting an edge on some of these will require much more than a simple sharpening stone. You might be able to put an edge on the knife, but the quality of the edge will be less than it originally was, and the knife will no longer provide whatever advantage it was originally designed to provide.

I would be more comfortable if the knives were rated. Something to the effect of: "for best results sharpened on a ceramic rod for a maximum of 20 times and return to maker for refinishing". Its all about using the right tools for the job. If we try to force the wrong edge on something with the wrong tool or technique we are probably inducing far more wear than we should be.

N2S

[This message has been edited by not2sharp (edited 06-16-2001).]
 
I rotate my knives enough that this will not be a problem in my lifetime. However, I am still worried about how to put a convex edge back on my Sebi when it gets dull...

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Wayne.
"To strive to seek to find and not to yield"
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