Razor sharpness compared to other types of blades

I always thought straight razors were about as sharp as a blade could get, but I've been told by a couple buddies that they aren't nearly as sharp as a scalpel or a Katana sword(or a couple other types of swords). I know it's possible, but I find it unlikely that these other blades can be significantly sharper.

I know the point of a straight is supposed to be a comfortable as well as sharp edge, but with the high quality steels used in them able to take a sharp edge with a narrow bevel, is there much room for improvement(in sharpness)?

I've seen some sharpness tests mentioned for comparison, like a loop of thread attached to a weight that shows the force required to cut the thread. But haven't seen results comparing different blades. Anyone have any info?

Bear in mind here that those blades are for different purposes.

A scalpel is for surgical operations, a katana is for slightly less accurate operations that dont require the subject to be walking around afterwards and a razor is for removing hairs on your face.

I've handled scalpels in the past that were certainly sharp enough to shave with, and I've used kitchen and pocket knives that could remove hair from your skin, but I wouldnt want to shave with either of them.

A straight razors edge is not necessarily any sharper than a scalpel but it is finer and wouldnt hold up to the same use as a scalpel or katana. Try using a straight razor for surgery and it would be dull in no time at all.

The razors edge would also be a lot smoother than either a katana or scalpel, simply because it needs to be in order to provide a comfortable shave withour wrecking your face.

A piece of steel will only get so sharp/thin before the edge collapses, and as Glen often says, anyone can make a piece of metal sharp. Smooth enough to shave with is another story!

I would also tend to disagree with the statement that scalpels are sharper than straight razors because I've handled both scalpels and straight razors and I know which one is easier to slice myself on..! You can touch a scalpels edge by mistake and get away with it if you're lucky. Touch a razor and it'll open your finger up like a piece of over ripe fruit every time..!

I'd be interested to see if there is any empirical data on this though.

Um, I always thought that Romulan battleaxes had the sharpest edges possible:

http://www.youtube.com/watch?v=XtdLTEr2r3Q

Yuck. Canned goo. Oh, and the fact that he was shaving with a battleaxe. And a 45 degree angle? Ouch. I mean, it's like his dad never taught him to shave witha battle axe.

Is that vid fake? Looks like when he was lathering up and the camera jumped ahead his face was clean shaven and just covered with lather. He probably then put the hair into the lather or something to show it coming off his face.

Anyways, yeahi know they all have different purposes and need different edges but I just want to know if they were all put through a standard test of sharpness. Like the thread loop test I mentioned, which blade would be the sharpest. I don't care of it dulls after one cut or stays sharp forever. This is a small bet we've got going, but would need some solid proof to decide.

Scalpel is a very broad term. Most of us have seen a basic Steri-Sharp™ plastic handled scalpel with a permanently 'loaded' #15 or #10 blade. While a useful clinic tool, this is the Bic razor of scalpel world and shouldn’t be confused with the array of tools being used in the operating room.

Modern manual surgical cutting tools are made up of reusable handles and disposable blades each fashioned for a particular task. It would not be far off to compare them with DE razors. In fact Feather of Japan makes many surgical blades.

Before lasers, the blades used for eye surgery were very sharp, very thin, and yes, very fragile.

So, some surgical blades are going to be sharper than your straight razor (or katana) but keep in mind they might be swapped or changed after only a few cuts.

OMG!...thats guts I think..hmm..lemme just look into my chest of stainless steel "objects" to compare :mace:
pcdad

Apparently, there's lots of these axe-shaving guys out there. Don't mean to hijack this thread, but shouldn't Lynn think about starting another website to serve this community? I'm thinking something like www.axerazorplace.com or www.triedtoshavewithanaxebutcutmyearsoffinstead.co m


YouTube - When a razor just won't do.

The fragility of the razor's edge is more related to its low bevel angle that its width dimension which may be .3 to .5 microns or something like that

The Tennessee toothpick was said to have one side w/ fine sharp edge the other more obtuse, for different uses. The japanese sword too saw different uses sometimes used against Jpn armor, foreign armor, or unarmored duels. There are some differences in cross sectional geometry from era to era, so do doubt there were different edges and final edge dimensions. Most likely they were as sharp as they could be for a given use.

If you are using a polish plane or similar finished-surface woodworking tool the solution for a chipped edge is typically to resharpen at a higher angle not to make it less sharp. Those edges are often just as fine dimension wise as the razor .5 micrometers of there'bouts. I dont see why a "katana" could not be as well; the best hope -a sword meant for unarmored dueling fresh from a highly skilled polisher, working on a very well made blade

Nevertheless a straight razor is typically as sharp as steel can get

Assume you have a sword, straight razor, and a scalpel made of the same steel. Sharpen each at the same included angle on the same hones. All will have the same edge sharpness... The only differences will be because of the blade thickness (i.e. the razor will flex more).

Keep narrowing the included bevel angle until the edge starts to chip or roll too easily. Increase the bevel angle slightly to obtain the maximum (in theory) sharpness available to the steel in use.

There are some "high tech", expensive sharpness testers available. The testing media used by the machines has to be very uniform and the standards are not very well agreed upon. Sort of a very niche product. Sharpness tester.

You're buddies are probably mistaken. I believe a straight can be made every bit as sharp as any other instrument. Mr. Parker could give us a good scientific explanation for this but I'll try on more laymen's terms.

Search for a link to the Verhoven paper. Professor Verhoven did a series of experiments on sharpness etc. Everything maxes out at a certain level (@4k). After that it's all about how smooth the edges of the bevel are. Modern production razors user teflon coatings and I suspect scalpels might as well. But whatever the circumstance the bottom line is I think straights can be made every bit as sharp as anything else.

Best Regards,
EL

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Originally Posted by burns420

Is that vid fake? Looks like when he was lathering up and the camera jumped ahead his face was clean shaven and just covered with lather. He probably then put the hair into the lather or something to show it coming off his face.

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Yeah, it was fake.

As per the topic, I'm sure a properly sharpened straight razor and a scalpel will be about the same sharpness, and could be used interchangeably to some degree.

A katana will not have as an acute angle as either of the above, but I'm sure it can be very sharp indeed and will probably hold its edge better.

BTW, I used to be an instructional aid for a college anatomy course, and have dissected 4 people. I know from experience that scalpels will get dull very fast. Give me a fresh scalpel and hot diggidy can that thing cut!

Shaving sharpness depends on the thickness of the apex of your edge (say .3 micron), the included angle of your edge bevel (say 10 degrees), and the rest of the bevel/blade geometry for a distance a bit wider than the thickness of your beard hair. Beyond these geometric characteristics a shave depends on the microstructure of the edge (call that localized roughness or granularity) this depends some on honing tools/techniques and some on blade alloy. A straight razor is not only honed at a low angle, the blade thickness behind that edge is almost straight (zero degree angle) behind the edge due to the hollow ground profile.

Old Japanese swords were honed to very low angles and were made of low-alloy steel that was pretty smooth grained, but just would not compete with the extreme low-angle geometry of a hollow ground straight razor. The japanese swords had to reasonably survive hacking at the non-steel japanese armor. They would get too badly dinged if they were tremendously hollow ground like a straight razor. To think that a samurai sword was a fine a shaving instrument as a straight razor is just silly. It is sharp of course, but in a different league.

The thin profile of a scalpel allows it to be as sharp as a razor. The only limitation is how someone (or some company) chooses to hone it. Since a scalpel cuts flesh which is softer than hair there is no reason not to hone it finer than a razor. They do make diamond microtomes (micro razors) that are much sharper than a razor, but also much shorter). For much scalpel work I would prefer a slightly rougher finish than a razor. There is a slight transverse slicing action used when cutting flesh that benefits from a little surface roughness. On a razor that might cause a bit of higher drag and a rough feel.

One big difference is the choice of blade alloys used for different tools. For an axe you might want to use one of the shock steels, say S7, but that doesn't take as fine an edge as say simple 1084 carbon steel. I do shave with knives. This works best with hollow ground blades made from a fine-grade razor purity alloy. For example AUS-6 alloy from Japan is relatively soft for a high end knife, but takes a very fine edge. I like alloys with vanadium in them (hence my user name) and find you can shave pretty well with a thin or hollow ground blade made from AUS-8, AUS-10, VG10, Sandvic 12C27, or even BG42. Thin geometry and either a simple carbon steel or a fine carbide stainless with elements like vanadium and tungsten in them let a knife get into the running as a shaving tool. Yet, in the end none of them have a paper-thin profile like a razor and are honed to that extremely thin profile like a razor. You can't even hold those thicker blades as close to parallel to your skin surface as you can with a razor. That is important in how your shave will feel.

I have been informed in the past that the ultimate waterstone on which to actually sharpen a razor is a 4,000 grit, and that stones finer than this, 8k 12k 30k whatever, do not so much add to the sharpness but rather smooth out and polish to make that same sharpness more skin-friendly. Is this true?

When sharpening on a "flat" abrasive surface we rely on the pressure on the exposed angles of the grit to be adequate to allow the blade steel to be scraped off. As grit size gets smaller the space between the grains gets smaller and also easily fills with iron debris. The contact area that the edge is honed upon gets higher and hence the pressure (force/area) goes down. If you try and overcome that increase in area with an increase in force you start to bend the apex of the edge over and overstress the material. That gets counter productive. You really do tend to reach a point of diminishing returns if you take a honing material and just try making the grit smaller and smaller.

However there are other ways to attack the problem. I believe that the disposable razor people don't use flat hones. Using optimally profiled wheels you can modify your contact area and probably benefit from reducing grit size beyond common limits. The other thing you can do is use a grit that is sharper than your average aluminum oxide. Different abrasives compounds are composed of minerals with different crystal structures. When I discussed the matter with Sal Glesser of Spyderco he mentioned that diamond crystals are not only hard, but they also have a sharp cutting profile. If your razor is stainless and has any hard alloying constituents a diamond hone might have benefits well beyond 4000 grit. However, diamond will not produce the same smoothness as another abrasive at a particular grit. So basically you can't quite get to an apples-to-apples comparison.

An edge finished with a coarser grit can pull more as you use it. It will drag on your skin and bite into hair and pull on it a little bit before cleaving. A smoother finish can give you a smoother feel. That difference would primarily be noticed right after honing is greatly reduced by the stropping process. If you use an extremely fine abrasive on your strop you might not notice the difference of your hone.

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Originally Posted by Blackpool

I have been informed in the past that the ultimate waterstone on which to actually sharpen a razor is a 4,000 grit, and that stones finer than this, 8k 12k 30k whatever, do not so much add to the sharpness but rather smooth out and polish to make that same sharpness more skin-friendly. Is this true?

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This is a very general statement that can be misinterpreted so I will say this in not correct. It may be more correct in saying that the 4k removes metal faster than the 8/12 and for sure 30k. The selection of hone would be dependent on the amount the edge is off optimum and how much time you want to invest to regain the edge qualities you desire. Think Barber's hone. For sure many of them are finer than 4k but only require a few laps to bring the edge back.

This is not a topic (hones) where generalizations will get you to the best path to take. Maybe refine the edge would be a better way to put it in place of just "smooth the edge".

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Originally Posted by JeffE

Um, I always thought that Romulan battleaxes had the sharpest edges possible:

YouTube - Shaving With A Battleaxe

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Isnt that a vintage Boker??

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Originally Posted by Blackpool

I have been informed in the past that the ultimate waterstone on which to actually sharpen a razor is a 4,000 grit, and that stones finer than this, 8k 12k 30k whatever, do not so much add to the sharpness but rather smooth out and polish to make that same sharpness more skin-friendly. Is this true?

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Joed already answered this very well, but I'll add this, just because:

You'd say a small paintbrush is for "detail work", but you could still paint an entire house with one.
It's still "painting".

All is clear now, I'm sure. :p

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Originally Posted by Blackpool

I have been informed in the past that the ultimate waterstone on which to actually sharpen a razor is a 4,000 grit, and that stones finer than this, 8k 12k 30k whatever, do not so much add to the sharpness but rather smooth out and polish to make that same sharpness more skin-friendly. Is this true?

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Not exactly, no. It's true that the edge stops getting thinner around 4k, but that's only part of sharpness; those striations catch on whatever you're trying to cut (beard hair), stopping the razor, making it pull. Higher cutting friction, basically. The finer & shallower those scratches become, the easier the blade slides through the beard & the sharper & more effortless it will feel. Beard toughness also plays a role--someone w/ a very light beard may not feel much of a difference in sharpness after 8k--mostly smoothness. Someone w/ a very tough beard, while still able to get a good shave off an 8k will most likely get a closer shave off of something finer (finisher, paste or whatever).

In short, sharpness has 2 components: the thickness of the very tip of the bevel (this tops out pretty early) & the polish of the bevel faces. Everyone's face will require something slightly different for best results.

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Originally Posted by PA23-250

Not exactly, no. It's true that the edge stops getting thinner around 4k, but that's only part of sharpness; those striations catch on whatever you're trying to cut (beard hair), stopping the razor, making it pull. ...In short, sharpness has 2 components: the thickness of the very tip of the bevel (this tops out pretty early) & the polish of the bevel faces. Everyone's face will require something slightly different for best results.

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I think all of this is true, but tends to focus the attention on the bevel faces at the expense of considering how microserration of the apex of the bevels affects the shave. If you take two sharp kitchen knives (one serrated and one smooth edged) and try and cut across a stick of wood using a whittling push stroke you can illuminate some significant effects. The smooth edge will not pass through the stick at 90-degrees. It will force the stick to bend away from the hand holding it and you will cut through at closer to 45-degrees. The serrated edge tips will dig into the stick and will fight the tilting of the stick and you might force the blade through at a lower cut angle, but there will be remarkable drag. In a sense the smooth edge will find a path of least resistance while serations will tend to push along to follow their points.

Before we drag this horse off to bury him/her, one question. Is there an additional component in sharpness is addition to the width of the edge and the smoothness of the sides of the bevel? Is that third component the angle at which the bevel sides extend away from the edge? It seems that the width of the very tip of the edge and the angle of the bevel sides might be necessarily connected, but I'm not sure that is the case. Wouldn't it be possible for the very tips of an acute angle and a slightly less acute angle to be equal and yet the angle formed by the bevel sides be different, thus affecting ultimate sharpness?

Right, I hope I am following this. On these last three responses, for which I am very grateful, would it be a fair assumption, borrowing your terminology, that the ultimate sharpness of the apex of the bevels is set at 4,000 whilst the bevel faces are further refined by subsequently higher grit stones, and furthermore goes some way to explaining why some people are greatly alarmed by the practice of taping because, I am guessing here, that would deepen the angle of the bevel and in doing so, make the bevel faces shallower?

I'm going to repeat part of what I posted earlier in this thread:
"Shaving sharpness depends on the thickness of the apex of your edge (say .3 micron), the included angle of your edge bevel (say 10 degrees), and the rest of the bevel/blade geometry for a distance a bit wider than the thickness of your beard hair. Beyond these geometric characteristics a shave depends on the microstructure of the edge (call that localized roughness or granularity) this depends some on honing tools/techniques and some on blade alloy. A straight razor is not only honed at a low angle, the blade thickness behind that edge is almost straight (zero degree angle) behind the edge due to the hollow ground profile."
Boy you know you are pompous when you start quoting yourself.
Again you learn a lot from trying to cut off a stick with a Boy Scout knife. How you cut through a tough cylindrical material depends a lot on the thickness of your blade up to the point where you pass all the way through the material. If you have to cut at about a 45-degree angle to slice through your blade thickness at 1.4X the material diameter is significant. My old scout knife did the job better than my Buck folding hunter which was better than my old pick-lock switchblade.

I know this probably a mistake to wade in here since you guys are getting techinical but here's my two cents from observation of people talking about swords. I do love katana, the traditional ones that take an army of people months to make not the ones that one guy hammers out in his back yard and sharpens up in a day. I've read books, watched documentaries and talked to people on the subject. As much as I love and respect them I have to point out one thing. A commonly used catch word for "sword" is "blade" as in when someone asks "What blade is that" they are really asking "What brand is your sword?" I've heard "blade" used interchangeably with "sword" in documentaries too saying things like "Katana are the sharpest blades ever made." (That point is also contested by European sword collectors btw.) The people watching the documentary then thinks "blade" means any sharp instrument and misinterprets. They then go around saying they have it on good authority that "Katana are the sharpest things ever made." See where I'm going with this? The blades aren't the problem. It's the choice of words.

Lori

Some years ago I was using a hanging strop and a 'noise off' startled me, making me forgot to flip the razor at the end of the stroke. It then on the next stroke simply carved its way straight through a 2.5" wide piece of cow leather over 1/8" thick, leaving me with two strops for the price of one! I mean, how sharp do you want these things to be? And as for katanas et al, I don't really suppose it matters to the less skillful combatant as he sadly contemplates his missing arm/leg/head that his sword was sharper than his adversaries'.
BTW I saw a test recently tween European Broadsword and katana on cutting through straw ricks etc. Both had about the same cutting power. So I guess it depends who practiced most when it came to a scrap!

May I recommend Experiments on Knife Sharpening - John Verhoeven ?

John Verhoeven is an authority on sharpening issues who did a lot of scientific experiments.

The katana actually has a rather obtuse cutting angle, even as swords go. It also has something that most European makers, including myself when I dabbled many years ago, consider anathema, the blade near the edge is actually convex, so that there is no line where the edge bevel joins the rest of the blade. This convexity of the blade is called "meat" in Japanese, and is considered crucial to catching the right balance between cutting ability and durability of the edge.
In fact there is quite some controversy among collectors and the swordsmiths who still make them. There is a tendency for enthusiasts in the sport of cutting straw-mat bundles to want swords with so little "meat" that they would be damaged by other use, and purists think this degrades the art of the Japanese sword.
There is, however, a variable with any curved sword which barely exists with the razor. The katana is curved, and inclines backwards from the handle. This results in the blade meeting its target at an oblique angle. The true cutting angle is the one at which blade to targe movement takes place, and is thus more acute than it seems.
I have a couple of books with interesting insight from India. The less surprising of the two is "Cavalry: Its History & Tactics" by Captain Louis Nolan, who played an uncertain role in sending the Light Brigade down the wrong valley, and was the first man to die in the Charge. He describes seeing fearful wounds inflicted by swords carried by Indian irregulars, but on examining them, found that they were surplus British army blades, rehilted, kept in a wooden scabbard instead of a steel one, but most importantly of all, made far sharper than they used to be in the British service.
The other is "Reminiscences of the Great Mutiny", by the former Sergeant William Forbes-Mitchell of the 93rd Highlanders, who unfortunately has left no record of standing in the Thin Red Line at Balaclava, but writes of the Indian Mutiny, in which the regiment stormed the Sikander Bagh to relieve the siege of Lucknow. His service did not require a sword, but he saw a great deal of death and wounds inflicted by them.
His conclusion was that western swords, made of something very much like spring steel and tempered to withstand the rather pointless of test of being bent into strong sideways curvature, had far less wounding power than those of Damascus steel, by which he presumably meant the Indian wootz steel which used to reach the west through Damascus. He held that being more rigid and deader in the hand, they wasted less of the impelling force by bouncing and vibrating.
I know some scalpels (I use the term with non-medical vagueness) can be as shallow-angled as razors. Supporting evidence for this is that obsidian flakes are used for certain types of surgery, even nowadays, and why would they do that, if they had never needed to extract the maximum possible sharpness from steel? Others, intended to contract bones, cartilege, tendons etc., were probably less sharp. The validity of cadaver tests in forensic ballistics, or evaluating weapons, is often held to be compromised by the fact that medical cadavers, being in short supply, are refrigerated and treated with preservatives, both of which toughen the tissues.

Clinicon Diamond Scalpel

Very impressive.

Ever shaved with one?

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Originally Posted by adbuett

Clinicon Diamond Scalpel

Very impressive.

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"Now, Mr. Smith, we'll just lance that boil with this diamond scalpel... there we go... feel better? Keep that hole filled up with neosporin. Just see Ms. Jaberwathy on your way out..."

"Hello Mr. Smith, unfortunately your insurance only covers boil lancing with a straight razor... That'll be $500,000.00 and We accept Visa, Amex and cash. How do you want to pay for that?"

All this talk about katana's makes me want one. I've got to be strong. :D

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Originally Posted by garth

All this talk about katana's makes me want one. I've got to be strong. :D

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They're nice but what are you going to do with it? A razor is much more practical.:D

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Originally Posted by garth

All this talk about katana's makes me want one. I've got to be strong. :D

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No, you don't. They are quite light and well-balanced. Why? Somebody has to do it.