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COTICULES REQUIRE LINEN

DJKELLY

Well-Known Member
OK, we all know that the coticule edge requires basically 60/60 linen/leather for peak performance. Has anyone a reason for this. Even with knife sharpening, if normal pressure is used to finish, though it is very rapid, it requires stropping to reach really sharp, but only less than a dozen or so laps and on just about any surface. I test a knife with paper, usually magazine stock, and prior to stropping six or seven tims it will cut, but drag. Afterward it absolutely glides through. I have to use many very light strokes to make up for stropping. A "Moon Stone" (ceramic) was the same way, and a Japanese waterhone is not. Any theories?
 

dnullify

Well-Known Member
I have a theory.

I think it depends on the hardness of the hone last used. finishing hones tend to be harder.
My theory is, that the contact with the dense hone creates a very keen edge, but also creates a micro-warping of the edge. Which is why it will clear away arm hair (spot contact with the keen edge), but why it doesn't glide through paper. When you strop it straightens out the already keen edge.

I noticed something like this off my spyderco UF, which is an incredibly hard and dense hone.

Just my thoughts.
 

Emmanuel

Well-Known Member
Denny,my question is how keep the honing angle stable.Do you apply the paper clip trick ?
By hand is almost impossible to keep a fixed angle.For my opinion that's the reason that you have the mentioned sense.Normally a knife needs 25 degrees like the woodworking tools. In the post photo you can see a jig for knife honing.
best regards
Emmanuel
 

DJKELLY

Well-Known Member
Honing angle is not the operative with what I mention. With or without a honing guide, the effect is the same. It might be an edge to the side, but every method I use to test the edge shows it is much keener after stropping. These include, shaving arm hair, TPT, hht or paper cutting. I think it must be a super small effect since I have not seen it with a scope.
 

Emmanuel

Well-Known Member
So your main question Denny is why the coticule edge is better after stroping? Do you know some
honing stone even Japanese that the prodused edge remain same after stroping? With my coticules
i can reach to HH4 ,but after stroping even the HHT doesn't improved the edge is smoother.Now concerning the knives ,surely they haven't same anatomy with razors.I believe that you produce a heterogeneous microedge and combing it after stroping the e sharpness capability strengthened.
Best regards
Emmanuel
 

Bart

Well-Known Member
Any honing leaves a microscopically dirty edge, possible first signs of corrosion (we're using water), debris deposits (as explained in prof. John D. Verhoeven's paper on knife sharpening), miscroscopic bur-like scructures (in as far they are not the same as debris deposits), and perhaps other anomalies.

Linen stropping, in my hypothesis, serves to reduce all that stuff. Most of that is achieved with only very few laps. This can easily be observed (see your 4 laps on jeans habit). For knives and tools, that's enough. An extremely fine paste on the surface of the stop (CrO or diamond) will speed this process up tremendously. But on a razor's edge we're dealing with the ultimate performance, not just the ultimate sharpness (as many of us feel an edge can be too sharp for a skin-friendly shave); but the perfect ratio between shaving hair and NOT blemishing skin. We don't want most of the debris gone, we want all of it gone. 60 laps has, through trial and error, been established as the amount that will get you there on most fabric strops. I am convinced that the first 5-10 laps do the most work, as to where the rest decreasingly does less and less work. If we weren't so persnickety about our edges (and we aren't about the edge of a chef's knive, because we're going to hammer it on a cutting board anyway), we wouldn't be bothering with going beyond those first 5-10 laps. In fact, I use a leather wheel loaded with diamond paste for a couple seconds and be done with it, if I strop at all (after honing knives and tools with a Coticule, I don't).

The clean leather that we use for a razor's edge has more of a burnishing action, which is expected to plastically alter the steel of the very edge. Also there, you can observe 80% of the effect after 10 laps. The remainder serves perfection.

A more elaborate explanation about
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is in the sharpening academy article about that topic.

Kind regards,
Bart.
 

vgeorge

Well-Known Member
Thanks for this patient and detailed explanation, Bart. Questions:

Why does a coticule edge particularly benefit more from the linen stropping? (Is that really true, or urban legend?)

In your judgment, are the plastic flows on the edge aided by leather stropping happen from just physical forces (rubbing action), or temperature changes from the friction (between leather and steel edge)?

Thanks.
 

Bart

Well-Known Member
vgeorge said:
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A valid question. I have always said that a freshly honed Coticule edge requires extra efforts on a linen strop. I didn't mean that as a direct comparison against other hones, but as compared to what most guys find a sufficiant amount of laps for "upkeep" stropping in between shaves. The freshly honed edge require more linen than the edge already in use. I noticed that some have made of it that I said that a Coticule edge requirs more linen than any other hone. I think that is an overly simplified interpretation. I do think however, that the finer the abrasives used for the finishing stage, the less linen stropping is needed. Chromium Oxide, for instance, does not require any linen stropping prior to leather (as long as you make sure not to transfer any CrO to the surface of the leather). I would also suspect that a Shapton 30K would not demand much linen, if any. But I don't know that for fact, because I don't own this hone. I do own a Chosera 10K, that one does require linen stropping in my experience, but less than a Coticule finished edge.

While sharpening, particles harder than steel plow throught the bevel. They remove part of the grooves they're drawing, but they also displace the sides of those grooves, without actually removing the steel. Part of the action is a buffing one, were the surface of the steel is more malled and plastered into shape, rather than purely abraded. I think that hones with particle hardness around 7.5 Mohs (Coticules) have a different abrasion/buffing ratio than hones with a particle hardness of 9 Mohs and more.
Furhtermore, on a polished steel surface, there is something called the Beilby layer. On a thoroughly worked surface, that layer extents 0.1 micron deep into the surface. If we know that that a cutting bevel consists of 2 sides that meet at a radius of approximately 0.4 micron, then 0.2 microns of that radius being "Beilby-fied", this becomes a very important factor in the behavior of the very edge. Some very interesting literature can be found here:
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This paper does not deal with sharpening directly, but several of the discussed principles certainly come together at the very edge of a razor, where the steel, due to it's thinness must be considered more "surface" than "core".
How the hone reformulates the steel structure, will certainly have an influence in what strops can do afterwards.

vgeorge said:
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I don't really know. We're dealing with processes at moleculary level here. Heat is essentially molecules loaded with kinetic energy. Molecules dance around eachother and the hotter they get, the more energetic they dance. Hence it's a form of movement. If we're going to force movement of molecules by rubbing with something that has enough friction, heat will be the result of that process. But not its cause, I would say.

Kind regards,
Bart.
 

vgeorge

Well-Known Member
Thanks for the detailed response. I had also been under the mistaken impression that you favored, and also that it was common wisdom, coticules need to be followed with more linen stropping than other hones. What you confirm here, that the need for linen stropping is inversely related to the fineness of the hone, makes eminent sense.

I am sure that is also only valid up to a point in the coarser direction. After a 1K hone, even days of linen stropping may not bring the edge to pleasant or acceptable levels.

Regarding leather stropping, my conjuncture is - but please do not underestimate my abysmal insufficiency of experience - friction increases edge temperature and that enormously aides the plastic flow from the pressure of steel meeting leather. Why I suspect this is due to a very simple, though unsystematic, observation. When I started stropping, I used to do it in slow stop-and-go steps of 5 for fear of damaging a beautiful strop from Chris. I had to do much more than an aggregate of 60 to see any discernible effect from the strop. Now, I can easily do 60 in one go, and the difference is very noticeable. It may have been my inexperience, but I think it is the steady friction on the edge causing the temperature to rise to permit plastic flow = polishing = formation of Beilby layers, etc. However, since that friction/temperature is highly localized, rest of the metallurgy remains largely unaffected.

I do not have the time to do anything immediately. But one day, I would like to check the results of stropping a warmed razor (dipped in hot water) on a warmed strop (using a cheap, mild heating pad from any pharmacy - people already warm strops by rubbing with their palms) and see what difference I can observe.

Not quite heeding to what Torolf said about just doing it. But in time ...

Thanks for your answers.
 

DJKELLY

Well-Known Member
This has covered my questions thoroughly and thx. As for heating a
Blade prior to stropping a hair dryer or careful use of a heat gun works well. D
 
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