Myth busted! Kai blade NOT super thick!

[ShavingByTheNumbers]

It has long been said that Kai blades are extra thick, super thick, or the thickest blades. This thinking might have started from what is stated at a major website, where Kai apparently sells their blades stating, "Made of a thicker gauge steel than other brands . . ." Is this true? Let's take a look at the new DE Razor Blade Dimensions Table in the ShaveWiki!

According to the table, which is based on rigorous measurements with many samples per blade, the Kai blade is 0.100 mm thick on average. However, out of the seven (7) different blades so far in the table, three (3) of them have a thickness of 0.100 mm. The BIC Chrome Platinum and the Derby Extra (Pre-2016) have the same average thickness of 0.100 mm as the Kai. Blade thickness generally ranges from 0.09 mm to 0.1 mm, so the 0.100 mm thick Kai blade is thicker "than other brands", as stated, but it is NOT thicker than ALL other brands. There are other blades with the same thickness, but the manufacturers of those blades do not make the statement that Kai apparently does. (Based on my unpublished measurements, it appears that there are other blades that are slightly thicker than Kai blades, so Kai blades do not appear to be the thickest blades, but I am not comfortable making a definitive statement without published data based on more measurements with more samples of those other blades.)

Myth busted.

 

[BSAGuy]

These guys are very excited about this revelation.

 

[BigJ]

Interesting. Thanks for pointing this out.

 

[ShavingByTheNumbers]

@BSAGuy: I hope that they would be proud.

@BigJ: You're welcome. My pleasure.

 

[Merle]

These guys are very excited about this revelation.

huh... I don't see it.
*maybe Kari... but...*

 

[Marcos1]

Is it some different type of metal then? I don't doubt the data but when I hold a Kai blade it has a noticeable resistance to bending than other blades which I guess some would equate as a difference in thickness. Why are Kai stiffer and more rigid feeling for most who use them do you think?

 

[DEdestroyer77]

Supposedly KAI's undergo a different hardening process or something along those lines. They are certainly more rigid than any other blade I've used, no question.

 

[Hoka Hey]

Definitely more rigid, and a touch wider. Love them in vintage Gillettes.

 

[ShavingByTheNumbers]

Supposedly KAI's undergo a different hardening process or something along those lines. They are certainly more rigid than any other blade I've used, no question.

This might be another myth.

Definitely more rigid, and a touch wider. Love them in vintage Gillettes.

Kai blades are wider than all others that I've measured, but I haven't measured all blades. Regarding rigidity, please keep reading...

Is it some different type of metal then? I don't doubt the data but when I hold a Kai blade it has a noticeable resistance to bending than other blades which I guess some would equate as a difference in thickness. Why are Kai stiffer and more rigid feeling for most who use them do you think?

That's a good question. First of all—and this is very important—the elastic modulus is fairly consistent across different steels, regardless of tempering. This seemed to be the case from a material properties table in one of my engineering books, but I did more digging and found this from someone who definitely seemed to know more than I know: "There are no apparent changes in elastic modulus in metals that have undergone different hardening treatments" Elastic modulus is directly proportional to stiffness, and with very similar elastic modulus from blade to blade, regardless of tempering or hardness, neither elastic modulus nor tempering or hardness can explain why the Kai blade feels stiffer than other blades.

Since material properties cannot explain significant stiffness differences among blades, what else is left? GEOMETRY! With basically the same geometry, steel blades should basically have the same stiffness. However, blades don't all have the same geometry, which means that some blades are stiffer or more rigid than others, even if the individual cannot feel any difference when comparing two blades because the difference is so small. The Kai blade's geometry alone explains why it feels stiffer than other blades:

1. The Kai blade has an average thickness of 0.100 mm, which is on the thick side. Stiffness is related to thickness cubed, so a 0.1 mm thick blade, whether a Kai or another blade, will generally feel 37 % stiffer than a 0.09 mm thick blade. There are other blades that I've measured with thicknesses of 0.100 mm or 0.101 mm: BIC Chrome Platinum, Derby Extra (Pre-2016), Dorco ST300, Feather Hi-Stainless, Personna Red, and Personna Lab Blue. Do any or all of those blades feel as stiff, if you can compare against the Kai blade? (I've compared the Kai to the BIC Chrome Platinum and I couldn't feel any difference.)
2. Out of all of the blades that I've measured, the Kai blade has the largest cross-sectional dimensions, but the tiny bit of extra stiffness due to this is probably not enough to feel. When you bend a blade to curve it along its length, W−CW is roughly and largely involved. Kai's value is 20.04 mm, while the average among blades that I've measured is 19.81 mm, so the Kai's value is only 1.2 % more than average, which isn't much and probably wouldn't be noticed. What about bending the other way, though? When you bend a blade to curve it along its width, L−CL (from the ends of the cutout to the ends of the blade tabs) is largely involved. Kai's value is 7.06 mm, while the average among blades that I've measured is 6.75 mm, so the Kai's value is 4.6 % more than average, which is also probably too small to notice.

Kai blades are more stiff/rigid than many other blades, but Kai blades are not really any more stiff/rigid than other blades that are also 0.1 mm thick. Maybe I should start a separate thread to really bust this "myth".

 

[Hoka Hey]

I'm guessing the stiffness is composition of the steel/heat treat/tempering.

There was a fellow that put blades under an electron microscope in spare time at work. Can't remember if he did a Kai. Might have to see if I can track it down.

 

[ShavingByTheNumbers]

I'm guessing the stiffness is composition of the steel/heat treat/tempering.

Stiffness/rigidity of the blade is not a material property of the steel, but a property that depends on the material AND the geometry of the blade. How stiff/rigid the blade feels when trying to bend it in one direction or the other is proportional to the flexural rigidity D, which is proportional to the elastic modulus E and is proportional to the cube of thickness T. (D is proportional to E*T^3.) This is why a 0.1 mm thick blade with elastic modulus E is 37 % more rigid than a 0.09 mm thick blade with the same elastic modulus E. The stiffness/rigidity that you feel when bending a blade is also proportional to the distance across the blade, perpendicular to the direction that you are bending the blade. The more distance, the bigger the cross section and the harder it is to bend the blade.

 

[Marcos1]

I appreciate all the effort that goes into all these informative posts. But I know what I feel...and there seems to be a consensus regarding Kai blades in particular with those that have used them that they feel and respond to flex in a different fashion to something that would be thicker or more rigid. How can so many people be so wrong when there's so many out there who have experienced this stiffness/rigidity etc specifically with Kai blades. I trust your math but even after just checking my stash again there is a different feel to them and there susceptibility to resist bending.

 

[ShavingByTheNumbers]

I appreciate all the effort that goes into all these informative posts. But I know what I feel...and there seems to be a consensus regarding Kai blades in particular with those that have used them that they feel and respond to flex in a different fashion to something that would be thicker or more rigid. How can so many people be so wrong when there's so many out there who have experienced this stiffness/rigidity etc specifically with Kai blades. I trust your math but even after just checking my stash again there is a different feel to them and there susceptibility to resist bending.

The big reason that so many guys feel that the Kai is especially stiff/rigid is because it is a thicker blade. When compared to other blades, it will feel as rigid or more rigid than other blades. I've compared the Kai (0.1 mm thick) to the new Derby Extra (0.09 mm thick) and the Kai feels stiffer. The calculation said about 37 % stiffer, and that seemed about right. I've also compared the Kai (0.1 mm thick) to the BIC Chrome Platinum (0.1 mm thick) and I couldn't feel a difference. As I wrote above, the Kai is slightly more rigid than other blades of the same thickness, but probably not enough to feel a difference. I'm glad that you've compared the Kai to other blades in your stash. Have you compared the Kai to the BIC Chrome Platinum, Derby Extra (Pre-2016), Dorco ST300, Feather Hi-Stainless, Personna Red, and/or Personna Lab Blue? Those are the only blades that I can say right now have the same or more thickness than the Kai blade. Bend one of these blades, them similarly bend the Kai, and go back and forth between the blades. If you can't definitely tell a difference, then the Kai is about as rigid as they are, which should be the case given similar material properties and geometry.

 

[John Clayton III]

Supposedly KAI's undergo a different hardening process ...

Cialis or Viagra maybe?