Sharpening, trailing vs leading

[samhain73]

Ok, most people sharpen a knife by pushining a blade into a sharpening medium,
ala whetstone, and even a sharpmaker crockstick style is a simular motion. Where as stroping and convexing are done by trailing, ie pulling the back of the blade twords you, and draging the blade on the stone. Now, if you were to simply pull a knife twords you on a whetstone, instead of a soft material, like a strop or mousepad setup, does it work as well for sharpening? Especially on a flat blade like a tanto? I wonder this as I look at a Strider tanto SnG, and try to figure out how to sharpen it without screwing up the "triangle of death". Does the The D&S Scary Sharp(TM) System work like this?

 

[PhilL]

ABS Master Smith, Murray Carter uses the pull method in his sharpening demos and I don't know anyone who can put a sharper edge on a blade.

 

[Bill DeShivs]

Either way works fine. Sharpening angle and stone grit are what is important.
Bill

 

[Cliff Stamp]

Now, if you were to simply pull a knife twords you on a whetstone, instead of a soft material, like a strop or mousepad setup, does it work as well for sharpening?

No, pushing the edge into the hone produces less of a burr and is directly better as a finishing step, for shaping it doesn't really matter. Verhoeven recently verified it directly experimently with micrographs comparing the two methods. People like Jeff Clark of course have been saying the same thing for years, he was the first person I read on the internet to note that there was a distinct difference between the two in burr formation. Of course if your steels are not prone to forming burrs, and you use very wide and aggressive hones, then edge trailing can still produce a decent edge.

-Cliff

 

[HoB]

I think it matters very much on the hardness of the hone. On hones that are hard (meaning you can not cut into them with the edge) I would prefer a leading edge for the reasons Cliff meantioned. On hones that are soft (can be cut with the edge) and that form slurries easily, I prefer a trailing edge because a) the edge doesn't "hop" over the abrasive particles anymore, b) the edge plows into the swarf, c) a slight angle misadjustment (which is pretty much unavoidable while freehanding) and the edge cuts into the abrasive medium, damaging both edge as well as hone, d) the swarf trailing behind the edge reduces burr formation greatly. All these points are of course only my personal opinion.

Personally, I have gotten much better results on my waterstones, ever since I have been using Murray Carters technique, but I still use my Sharpmaker with a leading edge and not like Murray Carter suggest with a trailing one. Again soft vs. hard hone.

 

[Bill DeShivs]

It constantly amazes me that some of you split hairs over sharpening!
Sharpening is not so much a technical issue as a practical one. I have been sharpening knives for about 40 years and can get them sharp enough to shave hair. How much sharper do you need? There may be a way to sharpen that looks better under a microscope, but practically- why? Knives are one of man's oldest tools and have benefitted greatly from modern technology, but sharp is sharp. I know of no surgeons who have their scalpels resharpened. If your knife is sharp enough to cut properly-that is all you need. If you can get it that sharp, and not scratch up the blade doing so, all the better. IMO anything further is overkill. You would think that 25 years ago people all used dull knives! They were as sharp then as now.
I know I always sound like an old grouch , and I really do understand researching and attempting improvement-but I really see no great innovations in sharpening here.
Bill

 

[HoB]

Well, in some respects I agree, in other I don't. I know for example that every surgeon often discards a scalpel after the first cut and declares it as unfit for surgery and requests a new one. Not because it dulled but it came insufficiently sharp or with an insufficiently polished blade a burr or nicks right out of the box.

We use razorblades in our lab to prepare ice surfaces. Only about 50% of the razorblades are "clean" enough for the task. And I am sure you know the experience were you unpack a brand new razor blade for your Gillette or Schick and you have the feeling that it pulls and scratches. Just because it cuts, doesn't mean the edge is really good.

 

[tim8557]

Well, in some respects I agree, in other I don't. I know for example that every surgeon often discards a scalpel after the first cut and declares it as unfit for surgery and requests a new one. Not because it dulled but it came insufficiently sharp or with an insufficiently polished blade a burr or nicks right out of the box.

We use razorblades in our lab to prepare ice surfaces. Only about 50% of the razorblades are "clean" enough for the task. And I am sure you know the experience were you unpack a brand new razor blade for your Gillette or Schick and you have the feeling that it pulls and scratches. Just because it cuts, doesn't mean the edge is really good.

Don't you think that much of the problem lies in making it "cheaper and cheaper" and disposable. The PA at a Hospital or group of hospitals puts it our for bid. Generally low bidder wins.

I'm sure that 30 years ago, surgeons sharpened their scalpels all of the time.

 

[Jeff Clark]

An edge produced using a trailing stroke may be sharper and better for your purpose despite (or perhaps because) it has a microscopic burr along the edge. A burr that is not very tall and is finely alligned with the edge can be very sharp. It will even stand up to moderate usage. If you strop or steel the edge it will respond by remaining sharp through more moderate usage. There are funny things that happen at the apex of a thin edge. The edge of a straight razor is described as having a "fin" which is not considered the same thing as a "burr", but sure sounds like one to me. This fin is said to "grow" with time. It is also delicate and can be torn off if you strop after shaving without letting the fin rest and grow.

Nobody would say that a straight razor is not sharp and nobody would say that you shouldn't strop it to maintain an edge. You just have to consider how light the work is that you ask a straight razor to perform. For a knife that I expect to use on somewhat tough material I get concerned to be sure that I have a solid foundation to my edge. I don't want to use power equipment for my last steps for fear of damaging the heat treatment or somehow overstressing the material at the apex of the edge. I also want to remove all traces of a burr since that is sort of overworked material by definition and may fold over and become a focal point for further edge breakdown. Some of this is just my conservative guesses of what I expect to be vulnerabilities of the sharpening process. I trust the manual edge-leading technique. I don't for example trust edges produced with a buffer. It is an issue of trust not an issue of scientific proof.

Many times in my life I have wanted a knife to have a very high slicing performance on meat and hide. I would often take an edge that was honed edge-leading and was fully deburred and strop it a few strokes edge-trailing with the intent of leaving a hint of a burr on the edge. This is a little bit like a magic ritual, but many blades shave better after the treatment.

My latest method to get a scary sharp edge involves a full edge-leading honing and deburring sequence followed by some stropping on photographic paper impregnated with submicron diamond dust. My hope is that this cleanly cuts the steel and doesn't significantly raise a burr. At worst it shouldn't raise much of a burr since I am not removing much material. Anyway this is what I do when I want to have an edge that cuts hanging toilet paper. This is not a practical test, but it shows that I am pragmatic about the issue. I'll do anything to get an edge that makes me happy.

 

[louisianacook]

Amen, for some of us it is not about practacality, but achieveing the pinnacle of what is possible in shaping a piece of steel. The fin on a straight razor and stropping after shaving is debatable like just about everything sharpening related. I personally shave with a straight razor from time to time and have experienced no detrimental effects by stropping afterwards. It has been postulated that this myth was a fabricated concept posed by the razor manufactures themselves in order to sell more razors. Makes sense to me considering you could concieveably get a lifetime of shaves from one straight razor.

Lee

 

[HoB]

and I really do understand researching and attempting improvement-but I really see no great innovations in sharpening here.

Agreed, its more like a rediscovery of a lost art.

Don't you think that much of the problem lies in making it "cheaper and cheaper" and disposable. The PA at a Hospital or group of hospitals puts it our for bid. Generally low bidder wins.

I'm sure that 30 years ago, surgeons sharpened their scalpels all of the time.

Absolutely!

This is not a practical test, but it shows that I am pragmatic about the issue. I'll do anything to get an edge that makes me happy.

Amen to that.

 

[Cliff Stamp]

...a slight angle misadjustment (which is pretty much unavoidable while freehanding) and the edge cuts into the abrasive medium, damaging both edge as well as hone

I have seen this with wood and leather hones.

The edge of a straight razor is described as having a "fin" which is not considered the same thing as a "burr", but sure sounds like one to me.

This is more of a myth than reality, pseudo-science and conjecture. Lee examined razors under high magnification and ideally they minimize burrs just like any other edge.

The issue of edges relaxing is a real one, this can be seen by just bending any elastic material and noting how it snaps back into place, the speed isn't constant because the force is proportial to the distortion.

I have done sharpness tests after work, after steeling and after delays to let the edge reset and there is a significant difference as the edge relaxes which is why if you want to hone before using not after to minimize metal removal.

...and can get them sharp enough to shave hair. How much sharper do you need?

That is about 25% of optimal based on what I have seen. Getting a knife sharper means the knife cuts better and stays sharper longer. Currently people are paying massive amounts of money for high end knives to get better edge retention, often improvments in small percentages, it makes little sense to not put as much effort into sharpening which it can make the same magnitude of effect.

There may be a way to sharpen that looks better under a microscope, but practically- why?

Because it works better, the microscope just lets you understand why it works better and to then use this knowledge to select in chosing blade steels, heat treating specifics, and so forth such as Verhoeven did when discussing AEB-L vs 440 series stainless for cutlery or Lee did when developing honing abrasives for Lee Valley.

-Cliff