Thread: Honing Sketch

Originally Posted by HNSB

With my stereo microscope I have observed what appeared to be rounding of a bevel from abrasive paste on a strop.
As I think about it now, it could simply be rounding of the back side of the bevel (where the angle changes into the main part of the blade).

You can very easily check which one it is with a marker, if a flat hone removes metal from the edge, then it's the back side of the bevel, if it removes metal from the back side of the bevel, then the strop had removed it from the edge.

True enough...
I just need to find the 5 minutes to do it.

Originally Posted by Martin103

Am i missing something! how can you create a convex edge from stropping aggressively or adding tape to a finished hone?
A correctly set bevel is perhaps 1mm to 2mm, adding tape to the back or spine of the razor changes the angle and does not create a convex bevel.

If you hone a razor and then on the final hone you add a layer of tape to the spine and finish the honing process with the additional layer of tape, I call the result a complex bevel in that it is not a single plane bevel. While it is not a smooth convex bevel, there are similar attributes.

Stropping a blade aggressively is another method of creating a convex edge. How loose is the strop?, what abrasives is it loaded with? How many trips does the edge make across the abrasives? While it may be at a very VERY small scale, the use of abrasives on a soft substrate causes curvature in the bevel.

Again, I am not trying to be argumentative or anything of that sort.
Weather the edge is beaten down and stropped back repeatedly, compressed/rolled and stropped back (possibly on a loaded strop), or some other cause...the result can be an edge that *I* have a hard time describing any other way that to say it has bevel shapes that exhibit convexity.

If it is not a PERFECT V edge, how would you describe it?

If you add that second layer of tape and go to work on the finish hone, does that secondary (or tertiary, depending on your nomenclature) bevel exhibit itself as a crisp angle, or does the angle change ever so slightly as the tape wears on that final hone?

I am totally splitting hairs here and I do not intend to make this into anything larger than it is. I am only trying to explain what I have observed.

Feel free to dismiss me and my observations. (seriously, I am new here and I am not going to get offended, nor do I intend to offend)

Originally Posted by gugi

You start with a bevel like this:
./\
/..\

When you add a piece of tape to the spine (or when you then strop on abrasive concave surface suche as a strop, or a dished out hone) you start removing metal from the very tip ending with
.^
/..\

If you look carefully you will notice that the angle at the tip (in blue) is now wider than it used to be (and still is in the red part), i.e. you have a convex curvature.

If you continue removing metal, eventually your whole bevel will become flat again as long as you use flat hone, or will match the curvature of the flexed strop/dished out hone (cf. pictures in post #4).

Many of us set the bevel with the spine taped (one layer) -- say, on a 1K lapped hone -- as in your second illustration. This continues with further honing -- 4K and 8K stones.

However, the problem is when we remove the tape from the spine -- say, for finishing on a pasted strop/hone. Then the geometry changes, and material has to be removed from the "shoulder" (where the blade meets the bevel opposite the blade's edge), before the cutting edge of the blade touches the strop/hone. OK, not entirely; that is, leather or felt are "cushiony" materials, so both the "shoulder" AND cutting edge encounter the abrasive, and THAT is what produces the "convex" bevel/edge.

Originally Posted by gugi

Yes, all of the above, but to quantify each piece you need to do real science. Plastic deformation in such hardened steel is orders of magnitude smaller than the abrasive effect. You probably want to check that 1930s article on how razors dull (answer: it's oxidation/rust).


It is possible that the preference is not the geometry of the bevel but how it's polished, i.e. if you create two very similarly convex bevels, one with a hone (and tape on the spine), and one with a pasted strop (using hard surface
and tape on the spine) would you notice the same difference. In other words by the time your bevel becomes convex through stropping between shaves there is a lot more happening to the edge. When making comparisons you want to eliminate as many of the additional effects as possible.

Trust me, I understand all too well the lack of parsimony in this problem.

And, while at points in my ramblings, it may seem like I am defending convex edges for razors, I am not. I think in most of my examples the mechanisms I describe for leading to the convex nature, generally are associated with decline in performance and a trip back to the hones.

I did, however, at one point allude to the fact that I have not intentionally ground on a convex bevel on a razor and tested a "fresh" convex edge...and in that regard, I am not ready to rule out the possibility that it could be beneficial (again, some disposable blades are ground with 3+ bevel angles and the result is basically convex...it would seem that there must be some logic behind producing blades this way....but obviously it might be problematic to duplicate their laser guided grinding on our straight razors)

I can only hypothesis that there may be some benefit to a convex edge on a straight razor...if someone has tested this, perhaps they can offer some insight.

You mention a paper that gives the answer that rust and oxidation is the cause of razor dulling. Really? It would seem that there might be more to it than that (again, not a snarky tone here...I just have a hard time with that). Glen suggest that an edge gets beat down and then stropped back out...I am inclined to agree with this idea...but we all know that metals generally can only be bent so many times before their properties change (often work hardening/becoming brittle/breaking). I have not read the paper though.

Originally Posted by JBHoren

Many of us set the bevel with the spine taped (one layer) -- say, on a 1K lapped hone -- as in your second illustration. This continues with further honing -- 4K and 8K stones.

However, the problem is when we remove the tape from the spine -- say, for finishing on a pasted strop/hone. Then the geometry changes, and material has to be removed from the "shoulder" (where the blade meets the bevel opposite the blade's edge), before the cutting edge of the blade touches the strop/hone. OK, not entirely; that is, leather or felt are "cushiony" materials, so both the "shoulder" AND cutting edge encounter the abrasive, and THAT is what produces the "convex" bevel/edge.

That is how in envision it, and have even directly observed this with knives with large bevels stropped on loaded leather using a guide. Perhaps razors are different in some regard, but I have a hard time understanding how.

I think you are attributing far too much metal removing power to a pasted strop. What is CrOx? 30K grit? 0.5 micron? Compared to a 1K bevel setting hone, what you are talking about on a pasted strop is like suggesting blowing on your morning porridge will produce a hurricane off the Florida Keys...

Here's some figures based on some formulae I derived (from Shapton data) a few years back:

Micron = 14755/Grit (source: http://straightrazorpalace.com/honin...onversion.html). Note there are margins of error on the constants in the formula since it was derived from sample data.

So that when setting the bevel and establishing the major geometry and shape of the edge, you are using something in the order of 14755/1000 = 14.8 micron abrasive particulates.

When polishing on a strop pasted with CrOx, you are using 14755/30000 = 0.5 micron particulates.

I'm putting my money on the 15 micron particles to win the geometry race on a razor's edge. That's not to say that, over time, you will not produce convex bevels off a pasted strop. The Grand Canyon was produced by water and wind. But like the Grand Canyon, it's going to take a little time to get there, IMO.

James.

I am not sure I have ever said Chromium oxide in this thread....I could be wrong?

I have seen sources for strop compounds MUCH larger than CrOx. Many here talk of CBN, and even the popular StraightRazorDesigns site offers Diamond sprays up to 2 micron.

Regardless of how convex it is, convex is convex. That is all I am saying.

Additionally, YES it will take some time to get there (thus the term "aggressive stropping").

Mountain out of a mole hill? Perhaps, but the action of stropping on a loaded strop is working on the apex (otherwise why do we do it?) it is this apex that will see the greatest magnitude of convex (I suggest). What is the apex width, a micron or two? That 0.5 micron CrOx starts to seem a little bigger when we drop to this scale and contemplate.

Hey, perhaps I am totally full of beans? I am just thinking out loud (or in text). I sincerely appreciate the intelligent discussion. Again, I hope my tone is understood...I am here to learn

here is an old thread which cleared things up for me with regards to pasted strops and convex wear.

Sure, no one got specific with the paste on the strop, but it is a fair assumption to suggest that most people don't set bevels with a pasted strop and rather use paste on a strop for touch ups or finishing. CrOx is a fairly ubiquitous addition to a strop, so I chose that as the example.

I don't disagree that the theory is all there ready to go in terms of pasted strops and convex edges. In fact, it is surely certain that this will happen given a long enough time frame and regular enough stropping. I'm not sure what you mean by 'aggressive' stropping in this context - I think normal, frequent stropping over a long time-period would do it.

However, after Glen experimented and showed his results, I believe the time frame necessary for a convex edge to develop to a point where it significantly differs from a linear edge (and yes, there are, theoretically, ways to quantify linear and convex and whether you have deviated significantly from one or the other) would be greater than the time between rehonings, other things being equal.

In any event, it is not really an important consideration in the overall scheme. A lot of people have a hard enough time getting a bevel set properly without worrying about whether their edge will become convex on a pasted strop. But it is certainly fun talking about it.

James.

Originally Posted by unit

I am not sure I have ever said Chromium oxide in this thread....I could be wrong?

I have seen sources for strop compounds MUCH larger than CrOx. Many here talk of CBN, and even the popular StraightRazorDesigns site offers Diamond sprays up to 2 micron.

Regardless of how convex it is, convex is convex. That is all I am saying.

Additionally, YES it will take some time to get there (thus the term "aggressive stropping").

Mountain out of a mole hill? Perhaps, but the action of stropping on a loaded strop is working on the apex (otherwise why do we do it?) it is this apex that will see the greatest magnitude of convex (I suggest). What is the apex width, a micron or two? That 0.5 micron CrOx starts to seem a little bigger when we drop to this scale and contemplate.

Hey, perhaps I am totally full of beans? I am just thinking out loud (or in text). I sincerely appreciate the intelligent discussion. Again, I hope my tone is understood...I am here to learn