Pretty Much What You'd Expect if Dovo1695 had a Shave Journal

[Rosseforp]

As it turns out, having good light is helpful for photography. I'm learning.

This image is a bit sharper. Certainly the ruler is. It's the same manual focus settings, so the early morning lighting must have helped. The window I photographed it in front of is East facing so that makes sense.

Still though, it's nowhere near as good as Dougs, and I don't think my 2 megapixel camera is going to get a heck of a lot better. It was designed with a wide angle lens and to take images from 2 feet away. A purpose built USB microscope is probably better suited for the task. A decent one like the Pluggable USB 2.0 is only $40. That's only two haircuts away, but I'm not a patient man. Maybe I'll sell a razor and buy one.

Nice

 

[Dovo1695]

Mike, I'm certainly one to historically have not been a fan of much gap having said many times that less is better. I'm not entirely sure there aren't factors beyond gap and blade exposure and rigidity about which I'm clueless.

I'm in the same boat. I think that the big 3 factors are rigidity, exposure, and gap, but I know their are tons of other elements in razor design that make a big difference in performance. I don't really understand most of it, but I'm trying to puzzle through it one piece at a time. What follow is very long so I did a little TLDR that covers it. I'm not sure it's right, but it seems right in my soap addled brain. I could be easily convinced that it is not true, because I have a habit of missing obvious things.

TLDR: Part of the reason the Lupo .72 is much more aggressive and so much less smooth than the GC .68 SB is that the hybrid guard has 50% less surface area, which means 50% less force is necessary to depress the guard into the skin, which increases effective blade exposure during the shave.
..............................................................................................................................................................................

We've been talking about how the GC .68 is way smoother than the Lupo .72 even though they have the same gap. I believe that positive vs negative blade exposure is a big part of that, but it's not the only reason why. The GC .68 SB is an actual straight bar razor, but the Lupo .72 SB is not. It's actually a hybrid SB like the Muhle R41.

I think the analogy of "gap" being like part of the suspension/braking system of the car is apt. The geometry and surface area of a razor cap/guard/gap is not just "like" a suspension system; it is a suspension system. It manages how pressure molds your highly plastic and elastic skin into contact with the blade. It manages the application and management of force just like any suspension system.

If we were shaving granite, razors would behave very differently. Many razors could not shave at all. Our skin is not like granite however, it's soft and squishy. It has high plasticity so it can be squished like clay, but it's also very elastic so it acts like a spring. By increasing pressure, we are able to squeeze skin into the gap and into contact with the blade, which lets us shave even with negative blade exposure. Whether or not we are able to do so has a lot to do with the surface area and shape of the guard. Every DE shaver knows that pressure plays a critical role in a good shave. The following is part of the reason why.

Consider that pressure is just force/surface area. Let's assume we're experienced GC .68 users and we intuitively and effortless exert exactly 100 newtons (I know that's a lot but it makes the math easier). Let's consider how that works with the following 3 guard designs.

First let's consider the Game Changer .68 SB guard. The picture below is obviously all squared off, but it illustrates the point nicely. The guard on the GC .68 SB has a surface area of 84mm. We divide our 100 pascal by 84mm and get a pressure of 0.84 pascal. So far so good.

What if we give the Game Changer .68 OC a try. It has the same gap and exposure and the same cap to guard geometry, so it should have the same aggressiveness right? Only if you're shaving granite. The OC guard system have a surface area of only 42mm. Now that exact same 100 newtons of pressure will yield 2.38 Pascal. That's twice as much! We don't need delve much into the plasticity, elasticity and deformation of skin to realize that your skin will squish and increase the actual blade exposure of the razor. Open combs are more aggressive given the same geometry, and RazoRock acknowledges that by listing The GC .68 SB as #6 in aggression and the GC .68 OC as #14.

What does this have to do with the Lupo .72? Well, it doesn't actually have a straight bar. It has a hybrid mix of SB & OC much like the like the R41 that most of us have tried at some point. Let's take a look at a hybrid guard using our 100 newtons of force. Take a look at the squared off R41 mockup below. You'll note that the combs actually narrow to a point, even further decreasing the surface area (in practice they're rounded off but that's a PIA to draw in Sketchup). Now we have a surface are of 11mm. Using that same 100 newtons of force, that's 100N/11mm for a total of 9.09 pascal. That's nearly 4x more pressure using exactly the same force! The scallops in the Lupo .72 guard are not as deep, but the same principal applies. Remember that a change of 0.05mm in blade exposure is massive change in aggression. The scallops don't have to be deep to have this effect; they just need to decrease surface area.

Here is a picture of the 3 of the razors we discussed, and the Fatip Piccolo to stand in as an example of a true OC razor. Guard surface area matters quite a lot. It acts like a suspension system managing pressure applied to the skin. The less surface area you have, the less pressure it takes to put your skin directly in contact with the blade, even with negative exposure. You can feel the difference in aggression.

Fatip Grande, Muhle R41, Lupo .72 SB, Game Changer .68 SB

 

[Chan Eil Whiskers]

I'm in the same boat. I think that the big 3 factors are rigidity, exposure, and gap, but I know their are tons of other elements in razor design that make a big difference in performance. I don't really understand most of it, but I'm trying to puzzle through it one piece at a time. What follow is very long so I did a little TLDR that covers it. I'm not sure it's right, but it seems right in my soap addled brain. I could be easily convinced that it is not true, because I have a habit of missing obvious things.

TLDR: Part of the reason the Lupo .72 is much more aggressive and so much less smooth than the GC .68 SB is that the hybrid guard has 50% less surface area, which means 50% less force is necessary to depress the guard into the skin, which increases effective blade exposure during the shave.
..............................................................................................................................................................................

We've been talking about how the GC .68 is way smoother than the Lupo .72 even though they have the same gap. I believe that positive vs negative blade exposure is a big part of that, but it's not the only reason why. The GC .68 SB is an actual straight bar razor, but the Lupo .72 SB is not. It's actually a hybrid SB like the Muhle R41.

I think the analogy of "gap" being like part of the suspension/braking system of the car is apt. The geometry and surface area of a razor cap/guard/gap is not just "like" a suspension system; it is a suspension system. It manages how pressure molds your highly plastic and elastic skin into contact with the blade. It manages the application and management of force just like any suspension system.

If we were shaving granite, razors would behave very differently. Many razors could not shave at all. Our skin is not like granite however, it's soft and squishy. It has high plasticity so it can be squished like clay, but it's also very elastic so it acts like a spring. By increasing pressure, we are able to squeeze skin into the gap and into contact with the blade, which lets us shave even with negative blade exposure. Whether or not we are able to do so has a lot to do with the surface area and shape of the guard. Every DE shaver knows that pressure plays a critical role in a good shave. The following is part of the reason why.

Consider that pressure is just force/surface area. Let's assume we're experienced GC .68 users and we intuitively and effortless exert exactly 100 newtons (I know that's a lot but it makes the math easier). Let's consider how that works with the following 3 guard designs.

First let's consider the Game Changer .68 SB guard. The picture below is obviously all squared off, but it illustrates the point nicely. The guard on the GC .68 SB has a surface area of 84mm. We divide our 100 pascal by 84mm and get a pressure of 0.84 pascal. So far so good.

What if we give the Game Changer .68 OC a try. It has the same gap and exposure and the same cap to guard geometry, so it should have the same aggressiveness right? Only if you're shaving granite. The OC guard system have a surface area of only 42mm. Now that exact same 100 newtons of pressure will yield 2.38 Pascal. That's twice as much! We don't need delve much into the plasticity, elasticity and deformation of skin to realize that your skin will squish and increase the actual blade exposure of the razor. Open combs are more aggressive given the same geometry, and RazoRock acknowledges that by listing The GC .68 SB as #6 in aggression and the GC .68 OC as #14.

What does this have to do with the Lupo .72? Well, it doesn't actually have a straight bar. It has a hybrid mix of SB & OC much like the like the R41 that most of us have tried at some point. Let's take a look at a hybrid guard using our 100 newtons of force. Take a look at the squared off R41 mockup below. You'll note that the combs actually narrow to a point, even further decreasing the surface area (in practice they're rounded off but that's a PIA to draw in Sketchup). Now we have a surface are of 11mm. Using that same 100 newtons of force, that's 100N/11mm for a total of 9.09 pascal. That's nearly 4x more pressure using exactly the same force! The scallops in the Lupo .72 guard are not as deep, but the same principal applies. Remember that a change of 0.05mm in blade exposure is massive change in aggression. The scallops don't have to be deep to have this effect; they just need to decrease surface area.

Here is a picture of the 3 of the razors we discussed, and the Fatip Piccolo to stand in as an example of a true OC razor. Guard surface area matters quite a lot. It acts like a suspension system managing pressure applied to the skin. The less surface area you have, the less pressure it takes to put your skin directly in contact with the blade, even with negative exposure. You can feel the difference in aggression.

Fatip Grande, Muhle R41, Lupo .72 SB, Game Changer .68 SB

Is there any way to like a post more than I like this one?

I'm not sure everything you said is accurate (and I'm sure you're not saying it is), but it is still hugely illustrative and helpful.

Happy shaves,

Jim

 

[Dovo1695]

I'm not sure everything you said is accurate (and I'm sure you're not saying it is), but it is still hugely illustrative and helpful.

Thanks for that. I'm not sure if it's true either, and I could easily be talked out of it. The points in the post above is a theory I've been advancing over in another thread so that others can do the hard work of explaining in simple terms that I can understand, the reasons why it is wrong.

Here are a couple more photos. I think they explain how it is possible that razors with negative exposure are even capable of shaving. They shouldn't be. They flat out wouldn't work on granite. When you depress a razor into skin however, you actually change the geometry of the shave plane relative to the blade and therefore increase exposure. I think this is especially true if you apply more force to the cap vs the guard or vice versa.

The first picture is a razor on granite. No matter how hard I push, this geometry and blade exposure will remain constant. The second picture assumes just enough force to depress the skin by 0.1mm. I show this by moving the red line down 0.1mm. The angle and everything else remains the same. It's not very much for skin to depress, but look at the difference in blade exposure. Depressing the skin this much takes almost no pressure; try it an see what I mean. I think this is why negative exposure razors are able to shave.

 

[hangblague]

Thanks for this. My mind usually wanders when someone starts talking physics, but this was like turning on the light.

 

[TinyT]

I'm pretty sure I remember Mike @Esox saying probably not many people use a Fatip Grande at a neutral angle. This is why. The blade exposure means you need to make an adjustment - either shallow or steep - to keep things comfortable.

 

[Esox]

The blade exposure means you need to make an adjustment - either shallow or steep - to keep things comfortable.

And/or you use a soap that makes your skin as soft, supple and forgiving as possible. I can use my Grande at a neutral angle with most blades but the limited pressure I apply makes it frustrating to get a close shave. I can use my MMOC at a neutral angle more easily because the blade is more stable but The Planer Effect can be an issue lol.

 

[Dovo1695]

It's been a while since I posted in my shave journal. I've been too preoccupied playing with USB microscopes to have much time left over for posting here. That's my excuse and I'm sticking to it.

True to form, my post is only tangentially related to shaving. I upgraded the 3 way mirror that I use for haircuts with LED lights. Since my shaving supply budget comes from the $20/month I save at the barber, I figure it counts. This weeks haircut will be financing a macro lens for measuring razor geometry. Come to think of it, maybe that doesn't even qualify as tangentially related.

Formerly, my lighting was an overhead USB shop light, which left much to be desired for blending fades. Adding the LED lights took about 5 minutes and cost $15 at Home Depot. It was worth every penny. At any rate, here it is in all it's glory.