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In Straight Razor Place Wiki there is a text about 'Bevel-setting in theory and practice'. The website link is Bevel-setting in theory and practice - Straight Razor Place Wiki
I do not understand the sentence 'But in our real world practice, we use flat abrasive tools, and those tools are only effective with flat bevel sides that lay in the same field as the imaginary field that touches the spine and the edge'.
Can someone please illustrate this for me with a sketch?
Thanks in advance.
I don't have enough time right now to make a sketch that would look any better than something my kids brought home from kindergarten.
Rephrased though:
In theory, a razor with a convex bevel could be honed on a concave hone with curvature that matches that of the bevel.
We use hones that are flat, therefore we need to have the bevels on our razor flat in relationship to the spine, so the hone is working on the bevel using the spine as a guide.
Maybe plane would be a better word than field in this case
Ok, so I threw together a sketch:
In the one on the left, the bevel is convex - it could be honed on a concave hone, but a straight line (flat hone) passes through the convex. That area would need to be ground away to work with a flat hone.
In the one on the right, a straight line connects the bevel and spine - this is what's desired when we hone.
Attachment 109359
Is it correct to say that the razor shown in the left drawing can also be honed on the hone shown in the right sketch? But not in reversed order?
Or in other words, you can hone every razor on a flat hone?
The one on the left could be honed on a flat hone - it will require grinding away the convex to get it flat all the way to the edge.
You would do that when you set the bevel on it. I guess the short answer is yes - any razor of good quality steel can be honed on a flat hone. Some will require a little more work to correct bad geometry.
Technically, the razor on the right could be honed on a concave hone, but every hone in the progression would require the exact same concaved surface, which is virtually impossible to accomplish in reality, and it would convex the bevel, requiring a new bevel set any time it was honed on any other hones.
Why is the convex stuff in the Wiki at all? What is the point? Who would hone on a convex surface? How do you ensure it retains the exact radius of curvature as it "dishes" over time? There's a reason we hone on flat surfaces.
James.
I think it's there to help establish the importance of flat hones.
HNSB, hoglahoo, Jimbo, thanks for your input.
Now that we are discussing honing issues, I have another question. Probably one that is harder to explain.
I do not understand the whole text shown under the headline 'Troubleshooting'. No matter how often I read this paragraph, it doesn't make sense.
Is there a better method to explain what point is made in this text?
Well it has certainly convinced me of the stupidity of convex surfaces... :p
James.
I am not sure I understand the idea of wanting to create a convex edge on a razor...but a lot of them are these days either from stropping aggressively with abrasives or adding tape for the finish hone (Zowanda method, I think)...technically they may be more of a complex bevel than a smooth convex...but hopefully you get the point.Quote:
Originally Posted by Jimbo
OTOH, I would not be quick to say convex surfaces are stupid...it is pretty easy to see that there is a bit more support behind the apex on a convexed edge and they tend to be a bit more durable in some regards (so long as they work well on your face;))
Yes. Sometimes edges are screwy because the razor is not a perfect triangle. Imagine the blade is a triangle with the spine as the base and the edge as the apex. On some razors the apex is not perfectly centred with regards the base. On other razors, the sides of the triangle are not perfectly straight lines. On some razors, both problems occur. On some razors, the issue can be quite extreme, though I have never seen (as the author of the wiki article states) a grind issue so bad that only one side of the bevel can be sharpened unless it is by design, like those Japanese blades or the microtomes or whatever they are called.Quote:
Originally Posted by strtman
The idea of honing is simple: rub both sides of the edge (the bevel) on an abrasive (flat) surface until the sides meet at a "fine enough" point. "Fine enough" can be pragmatically defined as whatever produces a shaveable outcome. Obviously, when each side of the bevel is taking turnabout on the hone, whether each side has the same amount of metal touching the hone becomes a consideration. Under certain circumstances, remedial measures are necessary on the hone. The rolling X-stroke is a way to undertake those remedial measures in some circumstances.
James.
Quote:
Originally Posted by unit
The surfaces are not stupid, the idea that you can maintain a hone with the exact radius of curvature necessary to impart precisely the same curvature on the razor each time you hone it is stupid. It is hard enough to lap a hone flat, let along make sure it maintains a certain curvature its entire life. Of course, you can accomplish it with some kind of rotating lapping wheel of certain radius, but I'll leave that to the experts and get by with my flat diamond plate.
Zowada 'adding tape' bevels are piece-wise linear bevels and are, from my reading of his posts at the time, a way for him to hone produced razors more quickly. The "robust edge" rationalisation came later I think, though I could be wrong there and apologies if so. Convex edges produced with pastes on on yielding strops are a side effect, not the primary goal. I also think Glen figured out that the convexing is minimal to the point of negligibility when considering the micron levels of something like CrOx paste compared to a bevel setter. But again, perhaps I don't remember that absolutely correctly.
James.
Jimbo, slow but sure it is all starting to make sense. Thanks for your extensive answer.
I think I could agree with everything you say.Quote:
Originally Posted by Jimbo
I would agree that a few stroppings on micron sized compounds would make only for a very slight convex...but it is slightly convex...and after MANY repeated stroppings the edge will convex considerably. Though, I am not sure anyone plans this intentionally;)
I would only suggest that in the world of cutlery, convex edges are quite a bit more durable. I am not suggesting that this concept could be applied to razors effectively, conversely I am not sure the concept can be completely dismissed until someone tests it thoroughly either. I have always been one to discuss symantics...and to your very valid point...trying to accomplish this with hard media does seem questionable for the average guy.
Sorry to ramble on an idiotic topic...but I will share that I watched an episode of "How It's Made" where they were making disposable razor blades and they had a series of bevels that I would characterize as "complex" and essentially was a "digital" representation of a convex bevel (i.e. a stepped collection of bevels that approximate a convex)...so it would seem that there may be some merit to the idea (if you have highly complex grinding equipment at your disposal):D
The troubleshooting section is for razors with warped blades. There is probably a better method, but I don't know what it isQuote:
Originally Posted by strtman
Looks like the editor is out again but I will try
Just to clarify my above posts: neither convex bevels or concave hones are desirable, in my opinion.
What it means is the spine and the bevels should lie flat on the stone.
That can happen only if the stone is flat and the razor has proper grind. Unfortunately all the requirements are not met all the time. Most notably the razor may not have been ground perfect or was improperly honed, then it will not completely lie flat on the stone.
Just to recap, a very flat stone, with a very flat razor, rub together, strop and shave/ repeat if needed.
Your welcome, tinkersd
Also in recap: Jimbo thinks convex surfaces are stupid.
Your welcome, HNSB.
However, YMMV.
James.
The problem is that the lack of any quantitative measure makes such statements meaningless.Quote:
Originally Posted by unit
Stropping on plain leather (the mildest stropping we use) removes material from the edge and therefore adds convexity (due to the flex of the leather). But how important is this, or any other level of convexity?
But there is no need to speculate. Fortunately one doesn't need a SEM and recollection of 5th grade math to quantify these things. Our natural 'measure' of a 'significant' feature is how fast it can be 'obliterated' by a standard honing procedure.
So, let's say one does 10 laps on a pasted strop with CrO before every shave, and let's use a big strop with say ~23"x2.5" of stropping surface. This is an enormous overkill that removes metal at about 50-200 times the normal rate. You can use the razor with this procedure over a month and then check how fast you can restore the convex edge on a Norton 8000. You'll find out exactly how many laps it takes to make the bevel flat again.
And, of course, if you use Norton 4000 or even Norton 1000 the number of strokes will be orders of magnitude less, so you can quickly convert a 'significant' convexity to and 'insignificant' one by using a different honing procedure.
I agree that honing demonstrates some convexity has been imparted on almost every razor I have honed...however, it remains un-proven HOW they became convex. Do they blunt/compress over time and use?, do they deform on the strop? Do they grind convex on a loaded strop? All of the above?Quote:
Originally Posted by gugi
Regardless, my findings/preferences (thus far) have shown preference for a nearly perfect V, that has been stopped considerably on bare leather (VVS convex?)
I have done quite a bit of testing on this over the years, this is one aspect that has continually come up...The simple reason it continues to appear is that in theory and scientifically it is true..-BUT-In practice everything falls apart, I did abusive testing on a razor with Diamond pastes considered by most to be the harshest, but after extreme over stropping and after 70+ shaves all the theroies were left hanging in the wind...That test is on the forumThe Micro-bevel and convexity ideas are easily disproved with simple honing tests, other then making honing easier they don't have any other function... Think it through, before voicing a differing opinion..Basically many of these thoeries are solid science but they having no effects in everyday use
I am not voicing a differing opinion, I am voicing different observations.Quote:
Originally Posted by gssixgun
Simply put, when I return to the hones with a razor, I start with a highest possible grit to hopefully remove the least amount of metal necessary. Obviously the associated "grinding" progresses very slowly, and I am able to see the action starting at the shoulder of the bevel, and eventually sneaking up on the edge.
I am not going on record as stating how the edge achieves this shape (that I interpret to have presumably been convex)...but I do know that the honing methods are the same with regard to the tape on the spine being from the same roll.
FWIW, the 3 razors I have done this with were all razors I honed previously, and basically returned them to the hones to repair a highly localized bit of damage (touched a toe to the sink, found a very tiny chip near the heel that I cannot explain, and wanted to just check on a third that I had shaved with for a few weeks)....perhaps my stropping is to "blame", but my shaves feel great.
I hope none of this comes off as know-it-allish or argumentative. I am only sharing data, hunches, observations, and occasionally experience gained from edge work on tools other than razors. I bow to the experience and wisdom available here, but humbly share my findings and hopefully am not doing so in an arrogant tone;)
You are banging the hell out of the edge with every shave, it pushes the edge farther back, you strop, and draw it back out and even again.. (Microscopically)
The cycle continues over and over, I wish I could do those cool computer graphics but alas I just don't know how :(
As the edge gets pushed back and dulls over time, when you finally hone you have to start at the shoulder and re-define the bevel... bringing everything back down and sharp again... This would appear on the bevel as wear at only the shoulder at first until the bevel gets defined into one even sharp angle again..
Now if you were to micro-bevel you could in theory only re-define the very edge instead of the entire bevel by lifting the angle and honing over the shoulder..
Am i missing something! how can you create a convex edge from stropping aggressively or adding tape to a finished hone?Quote:
Originally Posted by unit
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.
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).Quote:
Originally Posted by unit
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 surfaceQuote:
Originally Posted by unit
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.
You start with a bevel like this:Quote:
Originally Posted by Martin103
./\
/..\
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).
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). Honing leaves a sharp transition there; an abrasive strop would no doubt put a slight radius on the corner. That could cause similar lighting effects.
I'm going to add that to my list of things to look into when I have time.
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.Quote:
Originally Posted by HNSB
True enough...
I just need to find the 5 minutes to do it.
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.Quote:
Originally Posted by Martin103
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)
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.Quote:
Originally Posted by gugi
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.
Trust me, I understand all too well the lack of parsimony in this problem.Quote:
Originally Posted by gugi
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.
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.Quote:
Originally Posted by JBHoren
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.
Quote:
Originally Posted by unit
