Blade tension/stiffness

[wulfgar1976]

The earliest double edge safety razor was originally designed for carbon steel blades that were noticeably thicker than modern blades. When Gillette introduced the earliest "Thin" blade, it was carbon steel and would be stiffer than a stainless blade. This ultimately means that most of the blades in use to-day, being stainless, are held under less tension in a standard razor compared to when originally designed (standard modern razors haven't really changed the same basic design). Maybe that was what prompted the invention of the slant - the need to increase the tension for thinner blades.

From experimentation, a carbon steel blade or a Personna '74 is definitely more "aggressive" than a stainless blade. Razors I dismiss as far too mild suddenly become effective when paired with a carbon blade. Given that most blades these days are stainless, that perhaps explains why slants have gained popularity (or, conversely, why some people only use carbon steel blades) - because the tension/stiffness of a blade makes a noticeable difference (I do not subscribe to the "guillotine" explanation of why a slant is more efficient).

 

[silverlifter]

Kai are marginally thicker and wider than most modern blades, and apart from the additional blade feel, they do seem more efficient to me.

I don't agree about less tension in modern razors, though (assuming a Slim from the early 1960s counts as modern). Those razors really clamp down on the blade. Just as much as some slants, in my view, granted without the additional torque.

 

[APBinNCA]

I hate to say it, but you got me to look up the modulus of elasticity of several metals and there isn't a significant difference. If it is significantly different post heat treating then you would need proprietary information to establish that. If the blades were thicker historically, I would like some data on that like an engineering drawing. I have always wondered how thin Thin Blades were. Interesting discussion, if the right people find it.

 

[Medivh]

I was thinking the same thing, especially when I shave with my Old Type. The blades back then were thicker compared to the modern blades and we can only guess how the razors shaved back when they used those blades when they were fresh and shave ready.

 

[romsitsa]

Hello, the slant was patented as early as 1914 when the standard, three hole Gillette blades (and its clones) were available.
Wildes patent claims both added rigidity and slicing action: https://www.razors.click/patents/GB191403504/GB191403504.pdf

Have to add, that I never tried it, but an original Gillette blade is so rigid that it would most likely crack in a true slant, like a FASAN.

 

[ERS4]

Whether carbon steel or stainless steel, the elasticity and hardness of the metal can be controlled by appropriate heat treatment.

Especially now that the metal composition and industrial heat treatment technology are more scientific, the effect that can be mastered will only be more refined; therefore, the assumption that "carbon steel is harder than stainless steel" is out of fact.

Relative to the torque provided by "slant", I think "properly clamped insert" has a more direct effect on rigidity.
In particular, many of the excellent razors we know even almost keep the blades in a flat state, and they don't provide as much curvature as expected; there are also some razors that maintain a large curvature, but are prone to blade chattering.

 

[ShavingPanda]

I don't subscribe to material properties of blades making a difference, such as hardness or elasticity. I cannot imagine a blade would be under enough load or force to make a difference. Coatings on the edge I can see making a difference.

I think the biggest factor for a blade is support and curvature. Support being clamping on the top and bottom. For me, the Wolfman WR1 clamping of the top and bottom near the blade edge provides wonderful stability to the blade with no chatter. Another example is the b
Blackbird, with much more of the bottom of the blade being unsupported but the blade is curved so much that it provides stiffness. I think this is my slants work, they induce rigidity through torsion that reduces blade chatter.

 

[Paulford]

Unless you have blades finished to the same specs and the only variable is the material, it’s pointless to make comparisons.

On a traditional razor the curvature of the blade is on a different axis than the cutting surface and won’t have a meaningful effect across the cutting surface. That giant cutout I’m the middle of the blade negates all the theoretical stuff anyways.

I’m not convinced that slants actual produce any meaningful changes in the rigidity of the blade. I understand the theory behind it, I don’t think it’s possible to affect said changes and still have a presentable cutting surface. But that just an opinion, I know how to test it, but don’t have that kind of equipment.

 

[JPO]

The most important factor in blade rigidity is how the blade is supported. The simplest analogy is a cantilever beam.
The free length is raised to the power of three. So a small change in the unsupported length makes a big difference. A wider blade, provided it is the same thickness can be more flexible in the same razor.

The thickness of the blade (which factors in I) is also raised to the power of three.

So a small change in the unsupported length combined with a small change in the thickness can make a noticeable difference in blade rigidity.
It gets allot more complicated when the blade is supported on a fulcrum, relying on the spring tension of the curved blade.

The only way a slant razor can effect the rigidity of the blade is if it is designed in principle like a variation of the blackbird slanted.
If you slanted a razor head like the Henson the rigidity would not change much, if any.

 

[drb1956]

My daily blade is Wilkinson Sword(G), and it fits my Parker 91R perfectly, with no blade "chatter". I recently tried a Nacet blade that was piffed to me, and the blade chatter was more than I could shave with. Missed a lot of stubble, had to pull that blade, and finished with a Wilkie.

 

[tube_guy]

The most important factor in blade rigidity is how the blade is supported. The simplest analogy is a cantilever beam.
The free length is raised to the power of three. So a small change in the unsupported length makes a big difference. A wider blade, provided it is the same thickness can be more flexible in the same razor.
View attachment 1427091
The thickness of the blade (which factors in I) is also raised to the power of three.
View attachment 1427092
So a small change in the unsupported length combined with a small change in the thickness can make a noticeable difference in blade rigidity.
It gets allot more complicated when the blade is supported on a fulcrum, relying on the spring tension of the curved blade.

View attachment 1427093
The only way a slant razor can effect the rigidity of the blade is if it is designed in principle like a variation of the blackbird slanted.
If you slanted a razor head like the Henson the rigidity would not change much, if any.

Your conclusion that a slant would have to be designed like a variation of the Blackbird to affect blade rigidity assumes that the blade's moment of inertia doesn't change when it's twisted within a torsion type of slant razor. It most certainly does. That means the Bh^3/12 formula applies to the blade within a normal razor, but it does not apply to that same blade in a torsion slant razor.

I would agree that the increase in blade rigidity due to a torsion slant razor arrangement is likely to decrease as the blade is clamped closer to the cutting edge. However, it's not possible to clamp the blade right on the cutting edge, so there is likely to still be an effect.

 

[Steve_in_CT]

The problem I have with discussions about blade rigidity is that blade rigidity is not an effective predictor of anything in my personal experience. So to determine the factors that determine that rigidity is largely meaningless to me. Of the razors I have used, I have been told that the Fatip Piccolo and FOCS are on the high end of blade rigidity, but neither of those razors proved to be more efficient than less rigid designs like the Muhle Rocca or Merkur Futur. And the Fatip razors were less comfortable to use (for me).

 

[Esox]

And the Fatip razors were less comfortable to use (for me).

Increasing rigidity of the blade can have that effect for many. Something has to give, if the blade cant, the skin will through tugging. When I experienced that I started testing blades until I found the ones that suited my hairs composition. It makes a difference.

The difference most telling to me was using a Derby Extra, the green pre 2015 tucks that everyone loves to hate. In my R41, it skipped and tugged painfully first pass WTG on my cheek yet, in my Fatip Grande, its still a top 3 blade years later. Derby blades work for me far better than many more popular blades, GSB being one, but for me they need a rigid design to get the most from. That same effect also elevates other blades. The same holds true for a fresh Feather blade. It gives me a smoother more comfortable, as well as a much easier and quicker shave, in my Grande than in my R41.

The FOCS however, I'm one of the few I think that doesnt like it. Its not the rigidity of that blade, which is more rigid than in my Grande, but its the transition point of the torqued blade that I find scrapes my skin. The shallow side of the blade is fine and the steep side of the blade is fine, but the center of that blade, that scraping feeling, I just dont like.

 

[JPO]

Your conclusion that a slant would have to be designed like a variation of the Blackbird to affect blade rigidity assumes that the blade's moment of inertia doesn't change when it's twisted within a torsion type of slant razor. It most certainly does. That means the Bh^3/12 formula applies to the blade within a normal razor, but it does not apply to that same blade in a torsion slant razor.

I would agree that the increase in blade rigidity due to a torsion slant razor arrangement is likely to decrease as the blade is clamped closer to the cutting edge. However, it's not possible to clamp the blade right on the cutting edge, so there is likely to still be an effect.

The moment of inertia is a constant that does not change depending on the support constraints.

 

[JPO]

My daily blade is Wilkinson Sword(G), and it fits my Parker 91R perfectly, with no blade "chatter". I recently tried a Nacet blade that was piffed to me, and the blade chatter was more than I could shave with. Missed a lot of stubble, had to pull that blade, and finished with a Wilkie.

Funny you mention the Nacet blade. My Tatara razor has a really rigid blade support design. I recently got some Nacet blades. These felt softer in this particular razor then some other blades. I can imagine that this particular blade might not work as well in a more flexible blade support desig, like the R41, especially if you have coarse beard.
It would be interesting to know what is different about this particular blade. The Gillette Yellow blade works really well in my r41, but feel rough in my Tatara.
The difference in elastic properties of the different blades should not make much of a difference. Is the Nacet thinner?

 

[tube_guy]

The moment of inertia is a constant that does not change depending on the support constraints.

When the blade is bent by a force that is not parallel to h, the moment of inertia is not the same.

 

[JPO]

When the blade is bent by a force that is not parallel to h, the moment of inertia is not the same.

Bending the blade around two axis changes the spring stiffness you build up in the blade. As long as the blade is supported along two parallel lines the moment of inertia will not change.

 

[tube_guy]

Bending the blade around two axis changes the spring stiffness you build up in the blade. As long as the blade is supported along two parallel lines the moment of inertia will not change.

In a slant razor, the cutting force is not parallel to the blade thickness, h. That means the moment of inertia of the torqued blade is not based on a rectangular cross section. The moment of inertia of the twisted-up blade in a slant razor is not the same as a curved blade in a normal razor. This is in addition to any preload generated by the razor itself.

 

[JPO]

In a slant razor, the cutting force is not parallel to the blade thickness, h. That means the moment of inertia of the torqued blade is not based on a rectangular cross section. The moment of inertia of the twisted-up blade in a slant razor is not the same as a curved blade in a normal razor. This is in addition to any preload generated by the razor itself.

I think i know how a slant razor works. If the cutting edge was not a straight line, and the free end of the blade was twisted i would not want shave with the razor, but in this case it would be stiffer.
I am just a structural engineer that tries to explain this in my second language.

 

[APBinNCA]

The difference in elastic properties of the different blades should not make much of a difference. Is the Nacet thinner?

I believe the Nacet has a longer narrower bevel. I imagine in a well clamped razor that the bevel itself is all that is flexing and that it isn't enough to cause irritation, but enough to feel soft like automobile suspension. As for the yellows, I agree, but it is strange how lack of cutting can feel rough. Maybe it is adding extra force, not necessarily skin pressure. I am finding anything less sharp than any of the common Platinums(Gillette, Personna) not suitable for my Tatara.