Razor Blade Sharpness Chart

chris.hale said:
OK, so in the second part of your post you have finally acknowledged that weight is a measure of the FORCE the earth's gravity exerts upon a mass. Walking you gently through this, the scale is measuring that FORCE.

As you correctly point out, weight is referring to one specific force, gravity (or at least its effect on a mass), which is why newtons are used for measuring force in other scenarios. As the gravitational force on a 1kg mass on Earth is 9.8 newtons, you could attach your kitchen scale to the wall, press on it with your hand, and when it reads 1kg you're exerting approximately 10 newtons of force on it. 2 kg = roughly 20 newtons. This is how a scale can be used to measure force even though it reads in KG and not newtons. All a force meter is is a scale calibrated to display in newtons.

The amount of force required to push a blade through a consistent medium can be taken as a measure of its sharpness as a sharper blade will cut through more easily, hence if a blade requires 1 newton of force to cut through 1cm of medium, and another blade requires 5 newtons of force to make the same cut, the conclusion can be drawn that the blade which requires less force is the sharper of the two. This is how force can be used to compare sharpness, and how a scale calibrated in KG can be used to measure force.

I've done my best to clarify this, but if you're still not following I don't think I can help.
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Newton has also done his best to clarify this, but he is dead and i am tired. What you don't understand, is that when a blade cuts, it isn't subjected only to earth's standard acceleration. It has it's own acceleration the moment it cuts through. Which cannot be measured in weight (kg), because in weight, the only acceleration is one, the standard g (9,8 m/sec) of the earth.

This is why force is measured in Newtons and not in kg. Weight is measured to an object only when it is subject to the sole acceleration of the earth's gravity. On anything else, you measure force, in Newtons. And this is why factories pay for special machinery to measure sharpness, instead of rigging a scale and do that for pennies. And this is why when you hope on body scale, you don't move around to get the reading. A blade while cutting, is accelerating (see "peak force" in the link i posted above. If mass remains the same, how do you explain the existence of "peak force" in the type F=mass x acceleration? Surely, the blade isn't changing mass, right? Then what's changing? The acceleration of the blade. And this is why they use the paper medium in all the "normal" sharpening measuring devices and not a scale or static device.

On a sidenote, this is from another guy, apparently conducted in a lab with a self-invented mechanism. Strange that shows Feather and Kai as applying the max force, huh, while the guy with the scale has Kai close to Derby, isn't it...

https://mielabs.coe.neu.edu/sites/mielabs.coe.neu.edu/files/Razor Blade Sharpness Testing.pdf

Like you said, the scale, measures weight, which measures the force of earth's gravity, under the influence of earth's accelleration, which is fixed. That's weight. You don't measure sharpness by weight or cutting force for what matters.

Either that or the people who don't use scales are morons and pay money for useless equipment. And blades get sharper after shave #3.


That's all from me...

EDIT: Useful reading:

https://imada.com/what-is-a-force-gauge/
 
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There is subjectivity in interpreting objectivity obviously. Too many people confuse sharpness with smoothness. In layman's terms: they ain't the same thing. Sort of like measuring ductility as opposed to malleability as an example. Many confuse the two. The best blades seem to balance both sharpness & smoothness, e. g., the vast majority of Gillette blades he tested. It is utterly fascinating to me how Gillette has this down to an art with but minute differences that are surely a subtle "tweaking" of a given blade's hone angle and possibly the coatings to some degree. High tech for sure. Their consistency is simply beyond belief.
 
Obelix said:
Derby Extra
(Green) 53 44 51 49
Astra
Superior Platinum 49 46 44 46

So, assuming that lower number is sharper, in shave 2, a Derby is sharper than Astra in shave 2. Then Derby becomes duller, slightly so.

Similar to Astra, which starts duller, gets sharper, sharper. So shave 3 is the sharpest in the Astra and overall they are very close to sharpness with Derby.
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The Derby does start shave 2 sharper but does not finish the shave sharper whereas the Astra SP gets sharper after shave 2. There is a significant difference between the Derby and Astra SP after shave 2. The durability figures are interesting reading.
The first figure is for a new blade, second after shave 1, third after shave 2 and the fourth is the average. He only does 2 head shaves in his testing.
These figures correlate to tests done by Gillette in 1999 in relation to PTFE coatings on the blade edge;
"Along those lines you might also be interested in US5985459, a late-1990s Gillette patent that discusses the "second shave is the best" phenomenon. The authors found that this was due to excess PTFE on the surface. They removed that using some pretty nasty solvents. This made the first shave more comfortable, and their tests of cutting force showed little difference in blade life. Apparently there was still a functional thin film of PTFE on the blade, even though it was invisible at 900x magnification. Silicone oil beaded up on the coated blade, but spread out on an uncoated blade.

Figure 5 from that patent shows us another way to look at shaving comfort, in terms of cutting force or force to cut. The figure compares blade cutting a test pad of wool felt up to 500 times. With a PTFE coating the first dozen or so cuts take up to 1.8-lb of force, then the blade settles down to about 1.1-lb and slowly climbs to about 1.4-lb over the test. That initial variation is why some gents cork their blades or grumble about the first shave."
us5985459-5.png
 
Obelix said:
it...
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invicta said:
The Derby does start shave 2 sharper but does not finish the shave sharper whereas the Astra SP gets sharper after shave 2. There is a significant difference between the Derby and Astra SP after shave 2. The durability figures are interesting reading.
The first figure is for a new blade, second after shave 1, third after shave 2 and the fourth is the average. He only does 2 head shaves in his testing.
These figures correlate to tests done by Gillette in 1999 in relation to PTFE coatings on the blade edge;
"Along those lines you might also be interested in US5985459, a late-1990s Gillette patent that discusses the "second shave is the best" phenomenon. The authors found that this was due to excess PTFE on the surface. They removed that using some pretty nasty solvents. This made the first shave more comfortable, and their tests of cutting force showed little difference in blade life. Apparently there was still a functional thin film of PTFE on the blade, even though it was invisible at 900x magnification. Silicone oil beaded up on the coated blade, but spread out on an uncoated blade.

Figure 5 from that patent shows us another way to look at shaving comfort, in terms of cutting force or force to cut. The figure compares blade cutting a test pad of wool felt up to 500 times. With a PTFE coating the first dozen or so cuts take up to 1.8-lb of force, then the blade settles down to about 1.1-lb and slowly climbs to about 1.4-lb over the test. That initial variation is why some gents cork their blades or grumble about the first shave."
View attachment 30777
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In science, a theory to be accepted as true and not just a wacko theory, must 1) be able to the explain every situation , 2) must be accepted and reproduced by others.

In his measurements, there are non PTFE blades (even simple stainless) that according to him, get sharper as shaves progress. Assuming that the urban legend that human hair is tougher than copper filaments of the same caliber is true, as well as empirical experience that a blade usually withers with shaves instead of becoming sharper, the theory that could work for Derby, doesn't work for the rest. Even platinum coated blades, should not become sharper with use, since the platinum is put there are hardening agent, to prevent the edge of getting damaged early on.

At any rate, let us assume that i am wrong. Let us assume that this one is also wrong:
https://mielabs.coe.neu.edu/sites/mielabs.coe.neu.edu/files/Razor Blade Sharpness Testing.pdf

(Because, they can't BOTH be right, can they...).

I find it amazing, that people pay for that expensive machinery instead of such a simple method and that in engineering faculties, nobody has thought of it and even worse, teaches different things!

https://www.researchgate.net/publication/280821670_MEASURING_CUTTING_FORCES_IN_MACHINING_PROCESSES


99ew04.png


Or, instead of making students sleep, "grab a scale".

But, dem scientists, they want to overcomplicate things...
 
Obelix said:
In his measurements, there are non PTFE blades (even simple stainless) that according to him, get sharper as shaves progress. Assuming that the urban legend that human hair is tougher than copper filaments of the same caliber is true, as well as empirical experience that a blade usually withers with shaves instead of becoming sharper, the theory that could work for Derby, doesn't work for the rest. Even platinum coated blades, should not become sharper with use, since the platinum is put there are hardening agent, to prevent the edge of getting damaged early on.
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Indeed there are some results that are strange and I was not seeking to defend the results. The stainless steel blades like Astra SS do seem to get sharper and only the manufacturer knows what is on the edges that impedes the initial sharpness but then gets worn away in use. That improvement in sharpness is short lived and degradation of the edges continues with use as would be expected. The testing only goes as far as 2 head shaves so is limited in it's results.
The human hair can be as strong as copper wire of similar diameter in terms of tensile strength. It is the tensile strength that is often taken out of context because it has nothing to do with resistance to cutting by a sharp steel edge.
What the test results don't explain is smoothness. People have varying views on this parameter of a blade so that remains a mystery. Preparation, skin type, effects of UV on the skin all lead to a variation in blade performance.
I could not get to the mielab site which in not secure.
 
invicta said:
Indeed there are some results that are strange and I was not seeking to defend the results. The stainless steel blades like Astra SS do seem to get sharper and only the manufacturer knows what is on the edges that impedes the initial sharpness but then gets worn away in use. That improvement in sharpness is short lived and degradation of the edges continues with use as would be expected. The testing only goes as far as 2 head shaves so is limited in it's results.
The human hair can be as strong as copper wire of similar diameter in terms of tensile strength. It is the tensile strength that is often taken out of context because it has nothing to do with resistance to cutting by a sharp steel edge.
What the test results don't explain is smoothness. People have varying views on this parameter of a blade so that remains a mystery. Preparation, skin type, effects of UV on the skin all lead to a variation in blade performance.
I could not get to the mielab site which in not secure.
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Look, i am not a physicist, so i don't claim to be a scientific voice in this. However, until someone provides a document, video or anything from a scientific source, when using a scale is recognized as scientific method of measuring blade sharpness (or cutting force to make it more broad and easier to provide such proof), i stick with regarding "weirdness" as charlatanism. I mean, SURELY, someone else must have at least mentioned this somewhere in a paper in the depths of the internet, other than a shaver's blog!

I would also be very curious to hear, why his readings are right and the other guy's here

https://mielabs.coe.neu.edu/sites/mielabs.coe.neu.edu/files/Razor Blade Sharpness Testing.pdf

Are wrong. Because, the cases i see are:

1) They are both right. But their results are different, so there's a problem with this case.
2) One of the 2 is right, the other is wrong. Plausible, but i couldn't explain why.
3) None of the 2 are right. Plausible and a probable explanation is that none uses a scientifically approved method.
 
The Perma-Sharp surprised me and also clarified something.
The first shave was in a Star DE and I've had much better shaves with this razor.
The second shave was in a Slim set on 7 and it was a great shave. I put it down to the razor but it was also because the blade was significantly sharper on the second shave.
 
Obelix said:
...In his measurements, there are non PTFE blades (even simple stainless) that according to him, get sharper as shaves progress...
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He doesn't know what blades are coated with PTFE and neither do we. You are assuming that. Names such as "Platinum" & "Chromium" are meaningless and are more often than not merely sales pitches. All modern stainless blades have some coating lest they shave like the Treet "Black Beauty" that he tested. The coatings aid in smoothness obviously, but the sputtering and substrate metal/alloys are what holds the edge. That is where the rubber meets the road.
 
Bogeyman said:
He doesn't know what blades are coated with PTFE and neither do we. You are assuming that. Names such as "Platinum" & "Chromium" are meaningless and are more often than not merely sales pitches. All modern stainless blades have some coating lest they shave like the Treet "Black Beauty" that he tested. The coatings aid in smoothness obviously, but the sputtering and substrate metal/alloys are what holds the edge. That is where the rubber meets the road.
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Where the rubber meets the road for me, is one, single scientific source, that proves that his method can be used for accurate cutting force measuring. The rest, is pure speculation. Because also the other guy claims to measure the same thing and finds different things and others yet, write scientific papers and forget to mention "you can use a simple sensor such as a common scale".

Last post from me, because there is no point in trying to add anything else that i haven't said already.
 
Interesting but a bit pointless really.
I like knives and other sharp things and mostly I sharpen my own; axe, machete, penknife, cook's knife, paring knife whatever they are all different. Without knowing the relative hardness of the edges and the angle of the edge and how that relates to the angle of use, nevermind what treatments have been applied what does that test show?
 
Count of Undolpho said:
Interesting but a bit pointless really.
I like knives and other sharp things and mostly I sharpen my own; axe, machete, penknife, cook's knife, paring knife whatever they are all different. Without knowing the relative hardness of the edges and the angle of the edge and how that relates to the angle of use, nevermind what treatments have been applied what does that test show?
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Well it made for a lively debate if nothing else :) P.
 
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