Blade bevel angle

[blethenstrom]

A question that I has arisen in my mind over some time is the question of the Razor Blade Bevel Angle, not referring to shaving angle or anything like that, but just the angle at which the blade is sharpened. I have seen very little discussion regarding this on B&B and I really only found one other thread and it was pretty limited. Bevel angle of blades?.

The reason I am interested in this is just like a bevel angle on a knife has a vast impact on how sharp a knife feels and how durable a knife blade edge is. For example, a kitchen knife is often sharpened at 20 degrees to generate a very sharp knife to cut vegetables etc. However, a pocket knife is often sharpened closer to 25 degrees to generate a sharp, but not as sharp as the kitchen knife, but a much more durable edge.

Of course the steel and heat treatment of the blade material is very important as well, but the angle at which it is sharpened I believe have a lot of correlation to sharpness/dullness, comfortable/rough and the longevity of the blade. If anyone has some information regarding this it would be appreciated. Has anyone done any measurements? The thread that I linked above had a few blades with angles.

My general hypothesis is that the sharper blades have more of an acute angle, which also makes it feel a bit rougher and not have the durability. Also the reverse that a more obtuse sharpening angle there is less sharpness, but better longevity.

Let me know your thoughts.

 

[Dundee]

Slightly old thread, but I figured since no one has replied, I'll submit my two cents...

I sampled a wide variety of DE blades, and when measuring their thickness, I found that pretty much all of them came in to .004" +/- .0002". What's more, is that the bevel widths were all pretty similar too, but I never measured those until now. If you plug these figures into a very simple trig function, you can see the range of angles you'll likely be dealing with. For example...
intersted
((asin((.004 / 2) / .005) * 180) / pi) * 2 = 47.15 degrees
((asin((.004 / 2) / .010) * 180) / pi) * 2 = 23.07 degrees
((asin((.004 / 2) / .015) * 180) / pi) * 2 = = 15.32 degrees

So as you can see, a range of different bevel widths in .005" increments will result in a much wider range of angles. The difficulty is getting a reliable measurement for the width of the bevel, because it's really hard to discern differences much smaller than .005". At least for my eyes. But if you plot out things by .001" you can see the dramatically different angles you will end up with.

((asin((.004 / 2) / .010) * 180) / pi) * 2 = 23.07 degrees
((asin((.004 / 2) / .011) * 180) / pi) * 2 = 20.9 degrees
((asin((.004 / 2) / .012) * 180) / pi) * 2 = 19.18 degrees
((asin((.004 / 2) / .013) * 180) / pi) * 2 = 17.69 degrees
((asin((.004 / 2) / .014) * 180) / pi) * 2 = 16.42 degrees
((asin((.004 / 2) / .015) * 180) / pi) * 2 = = 15.32 degrees

As best as I can see...

Derby Extra = .011" wide bevel, 20.9 degrees
Astra Platinum = .010" wide bevel, 23.07 degrees
Bic Chrome Platinum = .015" wide bevel, 15.32 degrees
Feather Hi Stainless = .019" wide bevel, 12.08 degrees
Treet Platinum = .011" wide bevel, 20.9 degrees
Lord Cool = .011", 20.9 degrees
Gilette Platinum = .009" wide bevel, 25.67 degrees
Gilette Wilkinson Sword = .009" wide bevel, 25.67 degrees
Dorco St300 = .014" wide bevel, 16.42 degrees
Unknown Brand = .012" wide bevel, 19.18 degrees

Also keep in mind that with the difficulty of resolving bevel widths to increments equal to or less than .005", that some measurements I had to take twice, but I didn't do any averages. So for example, one Bic Chrome Platinum I had measured .005" which would have given it an angle of 47 degrees, but I realized it was probably just the light not allowing me to see that bevel face clearly and tried another that measured .015" inches. So take all those measures with a grain of salt.

The other thing to realize is that some of these blades don't have only one edge bevel. For example, the Bic Platinum ones had a very small micro-bevel that I could just barely make out thanks to the light, and trying to measure what angle it was at would be basically impossible with a set of calipers. To get more reliable measurements, and of small bevels like that, using a laser goniometer would be necessary.

Now, as far as how these geometries actually affect things, that's going to be a bit of conjecture on my part.

First of all, we have to realize that the type of cutting we're doing with shaving is in all reality an impact/chopping type of cut, on a very microscopic level. Many people would also say this as "push" cutting versus draw/slice cutting. With this type of cutting action, the size of the edge apex itself matters greatly, and the finish that the edge was polished to can greatly affect that. If you check out some of the SEM images available on Science of Sharp, you can see that the apex of a razor is typically 1-2 microns wide. In fact he has some SEM images of some common razor blades that closely match the calculations that I posted above.

An Astra blade.

Science of Sharp also defines "keenness" versus "sharpness"

Consider definitions from the Merriam-Webster dictionary:

sharp​

adjective \shärp\
: having a thin edge that is able to cut things

keen​

adjective \kēn\
: having a fine edge or point

These two adjectives will serve to describe

A) The thinness of the edge (sharpness) as quantified by the edge width at 3 microns from the apex.

B) The edge width or fineness of the edge (keenness) as measured at the very apex of the bevel.

These two words are colloquially synonyms; however, we require more precise definitions reflecting the subtle differences in the meanings of the two words.

So while most razor blades will be as keen (meaning they're the same size at the very apex) the thickness of the edge 3 microns back from the very apex is a function of the edge angle. A more acute angle, will mean a thinner edge 3 microns back, so a sharper edge. You could do the math to know what blades would be what thickness 3 microns back from the apex, but since they're all basically the same thickness (.004") it's not necessary; any blade with a more acute edge angle is going to be thinner 3 microns from the apex.

Here's a Feather blade, for example, with the accompanying caption

Cross-section of a Feather Super Pro Artist Club blade, often considered to be the “sharpest” commercial razor blade. The blade is coated with a fluoropolymer that is removed with the first use. The Apex width is approximately 50nm, keener than any of the commercial blades shown above. The width at 3 microns is 1.4 microns, due to the 19 degree final bevel angle.

When it comes down to push-cutting/chopping edge stability and cutting ability matter. Edge stability is the ability for the edge to withstand deformation from impact, and cutting ability is a measure of how much force the wedge mechanism that the edge forms takes to actually cut through something. A balance between these two must be reached, because while having a thinner (i.e. sharper) edge will make the force required to wedge through objects less, and increase cutting ability, it will also mean the apex is less supported structurally, which can result in less edge stability. In other words, the edge must be as thick as it can be to sustain stability and not deform when it hits hair, but also thin enough to cut that hair efficiently. So while it may seem at first that any edge with a more acute edge geometry will be sharper, that might not actually be true if the edge deforms before it can cut any hair. As everyone's hair differs, so does the optimal thickness of the edge. Throwing in things like micro-bevels can also greatly change things. Generally speaking, adding a micro-bevel can increase stability on an otherwise too-thin edge. However, as you suggested, things like heat-treat can also play into this, as a harder blade always has increased edge stability.

Keenness is also important too, because it's the apex that starts the cut. It won't really matter how thick or thin the edge is 3 microns up from the apex, if the apex is so blunt that it simply pushes the hair out of the way instead of cutting into it. When it comes to keenness, it's more a result of the finishing abrasive and how fine it is. The degree to which it matters varies, but you can basically make a reasoned assumption that if the particle size of a given abrasive is much larger than 1 micron, that it will be pretty hard to get an apex that's much smaller than 1 micron.

So in essence I agree with your stated hypothesis, however with the caveat that there's also a point at which a very acute geometry may not shave as well simply because the apex will deform before it ever cuts the hair, due to a lack of structural strength. In that instance, a blade with a more obtuse geometry may end up actually feeling sharper, and so it's not as simple as more obtuse edges having more durability. Especially because you could have an edge on a blade that's 56 HRC that is at 20 degrees, but it may be less resistant to deformation than an edge on a 60 HRC blade that's 15 degrees, because the hardness will be factoring into the edge stability to a larger extent at that kind of discrepancy.

Personally I would be very interested to know what hardness levels most of these blades are ran at, because it's a big piece of the puzzle.

 

[blethenstrom]

Slightly old thread, but I figured since no one has replied, I'll submit my two cents...

I sampled a wide variety of DE blades, and when measuring their thickness, I found that pretty much all of them came in to .004" +/- .0002". What's more, is that the bevel widths were all pretty similar too, but I never measured those until now. If you plug these figures into a very simple trig function, you can see the range of angles you'll likely be dealing with. For example...
intersted
((asin((.004 / 2) / .005) * 180) / pi) * 2 = 47.15 degrees
((asin((.004 / 2) / .010) * 180) / pi) * 2 = 23.07 degrees
((asin((.004 / 2) / .015) * 180) / pi) * 2 = = 15.32 degrees

So as you can see, a range of different bevel widths in .005" increments will result in a much wider range of angles. The difficulty is getting a reliable measurement for the width of the bevel, because it's really hard to discern differences much smaller than .005". At least for my eyes. But if you plot out things by .001" you can see the dramatically different angles you will end up with.

((asin((.004 / 2) / .010) * 180) / pi) * 2 = 23.07 degrees
((asin((.004 / 2) / .011) * 180) / pi) * 2 = 20.9 degrees
((asin((.004 / 2) / .012) * 180) / pi) * 2 = 19.18 degrees
((asin((.004 / 2) / .013) * 180) / pi) * 2 = 17.69 degrees
((asin((.004 / 2) / .014) * 180) / pi) * 2 = 16.42 degrees
((asin((.004 / 2) / .015) * 180) / pi) * 2 = = 15.32 degrees

As best as I can see...

Derby Extra = .011" wide bevel, 20.9 degrees
Astra Platinum = .010" wide bevel, 23.07 degrees
Bic Chrome Platinum = .015" wide bevel, 15.32 degrees
Feather Hi Stainless = .019" wide bevel, 12.08 degrees
Treet Platinum = .011" wide bevel, 20.9 degrees
Lord Cool = .011", 20.9 degrees
Gilette Platinum = .009" wide bevel, 25.67 degrees
Gilette Wilkinson Sword = .009" wide bevel, 25.67 degrees
Dorco St300 = .014" wide bevel, 16.42 degrees
Unknown Brand = .012" wide bevel, 19.18 degrees

Also keep in mind that with the difficulty of resolving bevel widths to increments equal to or less than .005", that some measurements I had to take twice, but I didn't do any averages. So for example, one Bic Chrome Platinum I had measured .005" which would have given it an angle of 47 degrees, but I realized it was probably just the light not allowing me to see that bevel face clearly and tried another that measured .015" inches. So take all those measures with a grain of salt.

The other thing to realize is that some of these blades don't have only one edge bevel. For example, the Bic Platinum ones had a very small micro-bevel that I could just barely make out thanks to the light, and trying to measure what angle it was at would be basically impossible with a set of calipers. To get more reliable measurements, and of small bevels like that, using a laser goniometer would be necessary.

Now, as far as how these geometries actually affect things, that's going to be a bit of conjecture on my part.

First of all, we have to realize that the type of cutting we're doing with shaving is in all reality an impact/chopping type of cut, on a very microscopic level. Many people would also say this as "push" cutting versus draw/slice cutting. With this type of cutting action, the size of the edge apex itself matters greatly, and the finish that the edge was polished to can greatly affect that. If you check out some of the SEM images available on Science of Sharp, you can see that the apex of a razor is typically 1-2 microns wide. In fact he has some SEM images of some common razor blades that closely match the calculations that I posted above.

An Astra blade.

Science of Sharp also defines "keenness" versus "sharpness"



So while most razor blades will be as keen (meaning they're the same size at the very apex) the thickness of the edge 3 microns back from the very apex is a function of the edge angle. A more acute angle, will mean a thinner edge 3 microns back, so a sharper edge. You could do the math to know what blades would be what thickness 3 microns back from the apex, but since they're all basically the same thickness (.004") it's not necessary; any blade with a more acute edge angle is going to be thinner 3 microns from the apex.

Here's a Feather blade, for example, with the accompanying caption

When it comes down to push-cutting/chopping edge stability and cutting ability matter. Edge stability is the ability for the edge to withstand deformation from impact, and cutting ability is a measure of how much force the wedge mechanism that the edge forms takes to actually cut through something. A balance between these two must be reached, because while having a thinner (i.e. sharper) edge will make the force required to wedge through objects less, and increase cutting ability, it will also mean the apex is less supported structurally, which can result in less edge stability. In other words, the edge must be as thick as it can be to sustain stability and not deform when it hits hair, but also thin enough to cut that hair efficiently. So while it may seem at first that any edge with a more acute edge geometry will be sharper, that might not actually be true if the edge deforms before it can cut any hair. As everyone's hair differs, so does the optimal thickness of the edge. Throwing in things like micro-bevels can also greatly change things. Generally speaking, adding a micro-bevel can increase stability on an otherwise too-thin edge. However, as you suggested, things like heat-treat can also play into this, as a harder blade always has increased edge stability.

Keenness is also important too, because it's the apex that starts the cut. It won't really matter how thick or thin the edge is 3 microns up from the apex, if the apex is so blunt that it simply pushes the hair out of the way instead of cutting into it. When it comes to keenness, it's more a result of the finishing abrasive and how fine it is. The degree to which it matters varies, but you can basically make a reasoned assumption that if the particle size of a given abrasive is much larger than 1 micron, that it will be pretty hard to get an apex that's much smaller than 1 micron.

So in essence I agree with your stated hypothesis, however with the caveat that there's also a point at which a very acute geometry may not shave as well simply because the apex will deform before it ever cuts the hair, due to a lack of structural strength. In that instance, a blade with a more obtuse geometry may end up actually feeling sharper, and so it's not as simple as more obtuse edges having more durability. Especially because you could have an edge on a blade that's 56 HRC that is at 20 degrees, but it may be less resistant to deformation than an edge on a 60 HRC blade that's 15 degrees, because the hardness will be factoring into the edge stability to a larger extent at that kind of discrepancy.

Personally I would be very interested to know what hardness levels most of these blades are ran at, because it's a big piece of the puzzle.

All I have to say is wow! That was a very detailed and good post. My engineering mind just consumed it all. I never really considered that the deflection of the blade apex would be a factor, but I see it now that the weaker the edge is the more deflection you will have and with more deflection comes more roughness. Having a stiff edge even if the bevel angle is a bit more obtuse can make the blade feel sharper. I completely agree.

Just to reiterate what you wrote. To make the edge stiffer you can:

1. Have a more obtuse bevel angle
2. Incorporate a double bevel which puts more material behind the edge
3. Utilize a harder, less flexible, steel.

More obtuse bevel angle is of course the simplest way to do this, but the balance is if you get too obtuse you get a blade that may seem dull and not cut very well.

Double bevel can be a good way to go, like you saw in the BIC case, to put more meat behind the edge. However, it will have the same cutting angle as if you did a single bevel at the double bevel angle. What it does buy you is a "relief" angle, which will help in the slicing motion of the hair. This is the reason why straight razors are hollow ground. All straight razors are double beveled.

Use a harder steel. Harder steel means brittle steel. This is the balance here. The harder it gets the more brittle it gets. There is a limit to how hard you can go without having the edge start chipping while shaving (ouch!).

To summarize a bit we can say that the rough feeling of a blade can come from a few sources. First if the blade is not sharp enough to cut it will feel rough. Secondly, the edge is deflecting while shaving causing discomfort. It still cuts, but it is rough. Thirdly, the blade edge is too hard and chips and this would feel really rough. Not sure if this is happening though.
-Boris

 

[Dundee]

All I have to say is wow! That was a very detailed and good post. My engineering mind just consumed it all. I never really considered that the deflection of the blade apex would be a factor, but I see it now that the weaker the edge is the more deflection you will have and with more deflection comes more roughness. Having a stiff edge even if the bevel angle is a bit more obtuse can make the blade feel sharper. I completely agree.

Just to reiterate what you wrote. To make the edge stiffer you can:

1. Have a more obtuse bevel angle
2. Incorporate a double bevel which puts more material behind the edge
3. Utilize a harder, less flexible, steel.

More obtuse bevel angle is of course the simplest way to do this, but the balance is if you get too obtuse you get a blade that may seem dull and not cut very well.

Double bevel can be a good way to go, like you saw in the BIC case, to put more meat behind the edge. However, it will have the same cutting angle as if you did a single bevel at the double bevel angle. What it does buy you is a "relief" angle, which will help in the slicing motion of the hair. This is the reason why straight razors are hollow ground. All straight razors are double beveled.

Use a harder steel. Harder steel means brittle steel. This is the balance here. The harder it gets the more brittle it gets. There is a limit to how hard you can go without having the edge start chipping while shaving (ouch!).

To summarize a bit we can say that the rough feeling of a blade can come from a few sources. First if the blade is not sharp enough to cut it will feel rough. Secondly, the edge is deflecting while shaving causing discomfort. It still cuts, but it is rough. Thirdly, the blade edge is too hard and chips and this would feel really rough. Not sure if this is happening though.
-Boris

One thing to keep in mind is that hair is not really very soft. I have heard it said that it can be as hard as copper is the same diameter. I think that's probably a little bit of an exaggeration, especially considering we tend to soften hair up with moisture before shaving, but it does still give a good idea of what forces the apex is encountering. Especially if you consider that the average hair is .003"-.005" thick, which is literally almost 100 times larger than an apex that's 1 micron. So I would say that the possibility for chipping is actually quite high, however I don't think that chipping at that level will be able to be felt as roughness on the skin, but rather just end up with tugging of the whiskers.

Plastic deformation of the edge would act differently in my opinion. As you said, it would be deflected, and so would probably end up not catching and cutting the hair at all. On the other hand, with a chipped apex, the hair is still so much larger than the apex that it could still cut, but with just much more force required, resulting in the tugging/pulling feeling. With am apex that rolls or dents, you could experience the same thing, but it could also just result in the hairs not being cut at all.

Another thing to consider is how the coatings come into play. Many people assume they're just to protect against corrosion, but I have read that they also provide a certain level of lubrication which allows the edge to pass through the hair more easily. That's why many razors seem to fall off in sharpness quite drastically after the first use, and why some very specifically tell you not to wipe the blade after use.

 

[DesertIguana]

Think the person who post post #1, should work for CDC, or NASA. This was very deep question.

 

[gpjoe]

Slightly old thread, but I figured since no one has replied, I'll submit my two cents...

I sampled a wide variety of DE blades, and when measuring their thickness, I found that pretty much all of them came in to .004" +/- .0002". What's more, is that the bevel widths were all pretty similar too, but I never measured those until now. If you plug these figures into a very simple trig function, you can see the range of angles you'll likely be dealing with. For example...
intersted
((asin((.004 / 2) / .005) * 180) / pi) * 2 = 47.15 degrees
((asin((.004 / 2) / .010) * 180) / pi) * 2 = 23.07 degrees
((asin((.004 / 2) / .015) * 180) / pi) * 2 = = 15.32 degrees

So as you can see, a range of different bevel widths in .005" increments will result in a much wider range of angles. The difficulty is getting a reliable measurement for the width of the bevel, because it's really hard to discern differences much smaller than .005". At least for my eyes. But if you plot out things by .001" you can see the dramatically different angles you will end up with.

((asin((.004 / 2) / .010) * 180) / pi) * 2 = 23.07 degrees
((asin((.004 / 2) / .011) * 180) / pi) * 2 = 20.9 degrees
((asin((.004 / 2) / .012) * 180) / pi) * 2 = 19.18 degrees
((asin((.004 / 2) / .013) * 180) / pi) * 2 = 17.69 degrees
((asin((.004 / 2) / .014) * 180) / pi) * 2 = 16.42 degrees
((asin((.004 / 2) / .015) * 180) / pi) * 2 = = 15.32 degrees

As best as I can see...

Derby Extra = .011" wide bevel, 20.9 degrees
Astra Platinum = .010" wide bevel, 23.07 degrees
Bic Chrome Platinum = .015" wide bevel, 15.32 degrees
Feather Hi Stainless = .019" wide bevel, 12.08 degrees
Treet Platinum = .011" wide bevel, 20.9 degrees
Lord Cool = .011", 20.9 degrees
Gilette Platinum = .009" wide bevel, 25.67 degrees
Gilette Wilkinson Sword = .009" wide bevel, 25.67 degrees
Dorco St300 = .014" wide bevel, 16.42 degrees
Unknown Brand = .012" wide bevel, 19.18 degrees

Also keep in mind that with the difficulty of resolving bevel widths to increments equal to or less than .005", that some measurements I had to take twice, but I didn't do any averages. So for example, one Bic Chrome Platinum I had measured .005" which would have given it an angle of 47 degrees, but I realized it was probably just the light not allowing me to see that bevel face clearly and tried another that measured .015" inches. So take all those measures with a grain of salt.

The other thing to realize is that some of these blades don't have only one edge bevel. For example, the Bic Platinum ones had a very small micro-bevel that I could just barely make out thanks to the light, and trying to measure what angle it was at would be basically impossible with a set of calipers. To get more reliable measurements, and of small bevels like that, using a laser goniometer would be necessary.

Now, as far as how these geometries actually affect things, that's going to be a bit of conjecture on my part.

First of all, we have to realize that the type of cutting we're doing with shaving is in all reality an impact/chopping type of cut, on a very microscopic level. Many people would also say this as "push" cutting versus draw/slice cutting. With this type of cutting action, the size of the edge apex itself matters greatly, and the finish that the edge was polished to can greatly affect that. If you check out some of the SEM images available on Science of Sharp, you can see that the apex of a razor is typically 1-2 microns wide. In fact he has some SEM images of some common razor blades that closely match the calculations that I posted above.

An Astra blade.

Science of Sharp also defines "keenness" versus "sharpness"



So while most razor blades will be as keen (meaning they're the same size at the very apex) the thickness of the edge 3 microns back from the very apex is a function of the edge angle. A more acute angle, will mean a thinner edge 3 microns back, so a sharper edge. You could do the math to know what blades would be what thickness 3 microns back from the apex, but since they're all basically the same thickness (.004") it's not necessary; any blade with a more acute edge angle is going to be thinner 3 microns from the apex.

Here's a Feather blade, for example, with the accompanying caption

When it comes down to push-cutting/chopping edge stability and cutting ability matter. Edge stability is the ability for the edge to withstand deformation from impact, and cutting ability is a measure of how much force the wedge mechanism that the edge forms takes to actually cut through something. A balance between these two must be reached, because while having a thinner (i.e. sharper) edge will make the force required to wedge through objects less, and increase cutting ability, it will also mean the apex is less supported structurally, which can result in less edge stability. In other words, the edge must be as thick as it can be to sustain stability and not deform when it hits hair, but also thin enough to cut that hair efficiently. So while it may seem at first that any edge with a more acute edge geometry will be sharper, that might not actually be true if the edge deforms before it can cut any hair. As everyone's hair differs, so does the optimal thickness of the edge. Throwing in things like micro-bevels can also greatly change things. Generally speaking, adding a micro-bevel can increase stability on an otherwise too-thin edge. However, as you suggested, things like heat-treat can also play into this, as a harder blade always has increased edge stability.

Keenness is also important too, because it's the apex that starts the cut. It won't really matter how thick or thin the edge is 3 microns up from the apex, if the apex is so blunt that it simply pushes the hair out of the way instead of cutting into it. When it comes to keenness, it's more a result of the finishing abrasive and how fine it is. The degree to which it matters varies, but you can basically make a reasoned assumption that if the particle size of a given abrasive is much larger than 1 micron, that it will be pretty hard to get an apex that's much smaller than 1 micron.

So in essence I agree with your stated hypothesis, however with the caveat that there's also a point at which a very acute geometry may not shave as well simply because the apex will deform before it ever cuts the hair, due to a lack of structural strength. In that instance, a blade with a more obtuse geometry may end up actually feeling sharper, and so it's not as simple as more obtuse edges having more durability. Especially because you could have an edge on a blade that's 56 HRC that is at 20 degrees, but it may be less resistant to deformation than an edge on a 60 HRC blade that's 15 degrees, because the hardness will be factoring into the edge stability to a larger extent at that kind of discrepancy.

Personally I would be very interested to know what hardness levels most of these blades are ran at, because it's a big piece of the puzzle.

Um, wow...very impressive bit of research.

I'm going to be perfectly honest and admit that I didn't read all of it. Still, I'm not at all surprised that two of the blades considered to be among the sharpest (by the membership) are the two with the most acute bevel angle: Feather and Bic...which, to me, adds credibility to your data.

Well done.

 

[blethenstrom]

One thing to keep in mind is that hair is not really very soft. I have heard it said that it can be as hard as copper is the same diameter. I think that's probably a little bit of an exaggeration, especially considering we tend to soften hair up with moisture before shaving, but it does still give a good idea of what forces the apex is encountering. Especially if you consider that the average hair is .003"-.005" thick, which is literally almost 100 times larger than an apex that's 1 micron. So I would say that the possibility for chipping is actually quite high, however I don't think that chipping at that level will be able to be felt as roughness on the skin, but rather just end up with tugging of the whiskers.

Plastic deformation of the edge would act differently in my opinion. As you said, it would be deflected, and so would probably end up not catching and cutting the hair at all. On the other hand, with a chipped apex, the hair is still so much larger than the apex that it could still cut, but with just much more force required, resulting in the tugging/pulling feeling. With am apex that rolls or dents, you could experience the same thing, but it could also just result in the hairs not being cut at all.

Another thing to consider is how the coatings come into play. Many people assume they're just to protect against corrosion, but I have read that they also provide a certain level of lubrication which allows the edge to pass through the hair more easily. That's why many razors seem to fall off in sharpness quite drastically after the first use, and why some very specifically tell you not to wipe the blade after use.

This with the coating being there for lubrication might have some merit. I was thinking of if during the cutting of the hair there is some drag and if the angle is a bit more more obtuse more lubrication is needed. Could also the coating help adding stiffness to the edge?

It all comes down to a balancing act to make a great razor blade. You have to have the right steel, right edge geometry, right blade thickness, right heat treat and eventual right coating to make a blade that is sharp but smooth and at the same time be durable. Many variables, so many ways to mess up.

 

[blethenstrom]

Um, wow...very impressive bit of research.

I'm going to be perfectly honest and admit that I didn't read all of it. Still, I'm not at all surprised that two of the blades considered to be among the sharpest (by the membership) are the two with the most acute bevel angle: Feather and Bic...which, to me, adds credibility to your data.

Well done.

Absolutely the Feather and the Bic are the among the sharpest of the bunch, but on the other end of that it seems like those who are using Feather blades are only using them for a few shaves before tossing. Of course there are some who use Feather blades for many many many shaves. Yes Excalibur folks I'm talking about you. If you look at average longevity of a blade I think you will find some other blades in that category.

 

[blethenstrom]

Think the person who post post #1, should work for CDC, or NASA. This was very deep question.

Please not the CDC!

 

[Invicta]

Razor blade design is quite complex and there are blades marketed for different regions as the hair growth (thickness) has a significant impact on the blade action.

I have heard it said that it can be as hard as copper is the same diameter. I think that's probably a little bit of an exaggeration,

That is often misquoted; the tensile strength of hair and cooper are equivalent but that has nothing to do with hardness. Tensile strenght is related to carrying a tensile load so has no bearing on shaving.

As you said, it would be deflected, and so would probably end up not catching and cutting the hair at all. On the other hand, with a chipped apex, the hair is still so much larger than the apex that it could still cut, but with just much more force required, resulting in the tugging/pulling feeling.

I think deflection is also related to the blade angle used. Steeper blade angles lead to higher lateral force on the blade edge which probably has a bearing on the higher incidence of chips on the cutting edge. The hair thickness will probably cause greater chipping but that would be an obvious conclusion; thicker hair is harder to cut.
Double bevel seems the way to go and I thought a lot of blades had a double bevel.

but I have read that they also provide a certain level of lubrication which allows the edge to pass through the hair more easily. That's why many razors seem to fall off in sharpness quite drastically after the first use, and why some very specifically tell you not to wipe the blade after use.

Polymer coatings are applied to aid lubrication and also help with resisting the build up of particles on the bevel. My experience is hard water does leave that scum on the bevel so I wipe (carefully) the blade after each use. The coating is baked on and cannot be removed by gentle wiping; non stick pans do not loose their coating due to washing although they have a much thicker polymer coating.

Could also the coating help adding stiffness to the edge?

I don't think polymer coatings add any stiffness as it is a very thin coating. Chrome and platinum are sputtered on the edge to aid hardness at the cutting edge.

 

[Dundee]

Double bevel seems the way to go and I thought a lot of blades had a double bevel.

I am wondering how many of the other blades I looked at also had a double-bevle/micro-bevel/relief-bevel. I only noticed it on the Bic blades because of the light, but it was so small that I expect I wouldn't have noticed it on other blades without higher magnification.

 

[blethenstrom]

I am wondering how many of the other blades I looked at also had a double-bevle/micro-bevel/relief-bevel. I only noticed it on the Bic blades because of the light, but it was so small that I expect I wouldn't have noticed it on other blades without higher magnification.

Given that it is that small I would say that it could be many more. Maybe it is a common practice.

 

[lasta]

I am wondering how many of the other blades I looked at also had a double-bevle/micro-bevel/relief-bevel. I only noticed it on the Bic blades because of the light, but it was so small that I expect I wouldn't have noticed it on other blades without higher magnification.

Most of the older blades I've come across have double bevel, or even a 3rd micro-bevel right at the apex (visible with a loupe).

Modern gillettes are the only single bevel grinds I've come across, either that or the micro bevel is so small it's hardly visible.

 

[blethenstrom]

Most of the older blades I've come across have double bevel, or even a 3rd micro-bevel right at the apex (visible with a loupe).

Modern gillettes are the only single bevel grinds I've come across, either that or the micro bevel is so small it's hardly visible.

Aren't most older blades thicker? If so it might have been "easier" to double bevel them and the modern blades are so thin that it becomes very difficult to do. Just some thoughts

 

[lasta]

Aren't most older blades thicker? If so it might have been "easier" to double bevel them and the modern blades are so thin that it becomes very difficult to do. Just some thoughts

I haven't noticed this actually!

I think most of the thicker blades comments refer to old carbon steel 3 holed blades before the 1920s.