Blade Grind: The oft ignored blade variable

[GreekGuy]

As I was answering a question regarding blades, I couldn't help think about blade grinds. Here is my reply copied from my original post


"I think the GSB is the sharpest blade out there, sharper than the feather.


There are many factors which affect blade feel beyond "how sharp" the blade actually is. The first big one is the coating, the second is how aggressive the razor is (blade gap and angle), and whether its open comb or bar can play a large role as well.


The last, and very largely ignored variable, is the blade grind. In my experience, Gillette blades are ground in a certain way, meaning, the bevel is at a certain angle. These vary from brand to brand. If I recall correctly a feather blade has an extra bevel compared to the gillette blades. Whether that is good or bad is open to debate. However, it is important to adjust your technique when using different blades in razors. Many gents find a blade / razor combo they like and stick with it. I personally like variety, but whats good in one razor is not in another.


I'm making a big deal about the grind because to me, thats the biggest difference between the GSB and feathers. I prefer the GSB, but those used to feathers may not find it as intuitive initially"


So what do you gents think? Have you noticed this between brands as well? I think its a factor a lot of people don't really pay much attention to when switching blades, but can make a big difference, and can explain why so many shavers disagree about blades. How one can think a blade is rough and another find it smooth. Obviously this is a complex issue, but I thought this point was worth calling attention to.


Discuss

[dharasick]

If the coating usually wears off after the first shave, why does that affect sharpness so much? From my reading it's my understanding that the coating is more to protect the blade's shelf life more so than blade quality.

Also don't forget an important part of razor aggressiveness--how far the blade protrudes out from under the cap.

I've been thinking about why blades are so different for different people and the source of those differences. Is it technique? Blade angle? Blade/Razor combination? Face texture/sensitivity? I wish we could do some real science on this, not 'bro-science.'

[Useless shaver]

Very interesting matter.

I'm quite ignorant, but I agree: common sense tells me that blade bevel must be very important (to what extent?). In fact that's how the blade edge touches the skin.

[inspiringK]

I think this may be talked about but done so without knowing. We typically use the terms "sharpness" and "smoothness" in reference to a blade's performance, but we could use "bevel angle" and "polish" instead.

Often in comparisons of one blade over the next, the term "sharpness" itself could be substituted with "shallow bevel" seamlessly. So, sharper blades tend to have shallower bevels. I would guess that Feather has the shallowest bevel grind.

Then, the term "smoothness" simply refers to the polish and uniformity of the cutting edge. A smooth blade will have less visible scratches under a microscope and will have a straighter edge under a microscope. To stick with feather, my guess is that they would look rough under a microscope (compared to say a Red Personna).

[barrycv]

I believe a different grind is the main physical difference between Personna Med & Lab.

[mblakele]

If the coating usually wears off after the first shave, why does that affect sharpness so much? From my reading it's my understanding that the coating is more to protect the blade's shelf life more so than blade quality.

Depends on the coating, I believe. PTFE is soft and will wear off easily. Harder materials should stay around longer. Some folks attribute the longevity of the P74 to its titanium coating. Here is what Gillette says about the Fusion blades ca. 2009, from http://www.pgdermatology.com/downloa...WhitePaper.pdf:

Each of the five stainless steel blades are at least as sharp as
a scalpel and are enhanced with a proprietary diamond-like carbon coating, as well as
an antifriction telomer layer to increase strength and glide (see Figure 9).

Here is that "Figure 9":



Presumably those coatings are not to scale, or else the coatings must increase the tip radius significantly. Using DLC for hardness seems to be http://www.google.com/patents/US5142785 from 1992. In 1994 http://www.google.com/patents/US5295305 seems to cover Gillette's use of Niobium and other binding agents between coatings. I think both of these patents have expired in the last couple of years, so we might start to see other blade companies using DLC coatings. Of course, the blades might cost more too.

[Pkrankow]

If you read about honing straight razors there is a lot of discussion about bevel angle (and use of tape when honing) but it boils down to steel can only take a certain fineness of angle for the edge or the material is too thin to support cutting. Typically this is around 17 degrees for straight razors. This applies to all makes, materials, and ages. It is safe to say it is a guide more than a law though as there is variation about this angle as blades are made and wear differently, yet preform admirably.

http://coticule.be/wedges.html

I do not know what the included bevel angle is on production safety razor blades, but I would expect it to be in the same range because the same type of material is being used. I am sure that different brands have slightly different bevel angles, and the same brand coming off a different machine in the same or another plant may have measurable angle difference.

I would argue that the abrasives used, the machining tolerances, and other manufacture maintenance variables would have much more impact on the performance and feel of the edge than the bevel angle, since the material choice limits the allowable bevel angle choices.

Phil

[dharasick]

Good stuff there mblakele.

[jwilock]

The coating is also important. Simply think of how hard it is to cut a piece of soft cheese. If the blade "sticks" to what you are trying to cut it won't glide through it smoothly no matter how sharp it is. Now maybe all blades have the same degree of "stickyness" to them when cutting through whiskers. I really don't know. But it is certainly easy to think that a certain type of coating might give one blade an edge (no pun intended) over another even if they are ground precisely the same way.

[woodfluter]

I don't have time to find it now, but someone on this forum loves to play with reflected-light microphotography and has very good gear. He posted a bunch of comparative blade edge photos that are excellent. Removes some of the guesswork.

I have looked at different blade bevels under a stereo microscope and they do differ. As I recall, Feathers had three bevels (many others only had two), and the first two were sort of rough in polish, but the final one (which counts the most) was quite narrow but exceptionally smooth and uniform.

About coatings. I think PTFE and similar are of value mostly in protecting the blade before use. They may also reduce drag for as long as they last, but if you look at the Fusion diagram Mblakele posted, obviously you cannot cut effectively with plastic so the end part of the telomer coating has to break off or be worn off right away. Leading me to think the rest of the coating near the bevels will follow shortly. However, they may remain in the depressions of the grind marks and thus serve to smooth things out better than I think.

Metal "coatings" are a different matter, are they not? Should be firmly bonded to the substrate metal. And capable of holding an edge and cutting.

About grind angle limitations. For cutlery steels, there is a very significant difference in the allowable grind angle depending on the specific alloy. And of course, assuming a similar application...with different angles being appropriate to differing uses. You can get away with a very low angle on a razor or razor blade because you aren't trying to cut wood or rope etc, things that would rapidly break off bits of the edge on a hard steel. Little hairs are easy. With older, conventional knife steels I won't attempt anything under 22 degrees per side, and often not that. With some high-tech steels I can go as low as 16-17 degrees per side and the edge is durable.

[redtide]

Regarding the Personnas 74, they where made from Tungsten with a Titanium coating "74" meant the atomic number of Tungsten. They use Tungsten to manufacture rocket engine... so where talking some tough steel. To bad the 74's are almost impossible to get.