Thread: Razor sharpness compared to other types of blades

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

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.

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.

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?

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".

Originally Posted by JeffE

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

YouTube - Shaving With A Battleaxe