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On blade angle

Ladies & Gents - Because it is coming up regularly, and pictures are often requested, I decided to make some crude diagrams depicting aspects of the dreaded blade angle.

To start out with, let's define the terms:





That is easy enough. I took a basic Merkur as my model. The following discussion may not hold up for other razor geometries, but the principles should be easily transferable.

Note that the cap is curved more at the top than at the bottom. In other words, the radius is smaller at the top than at the bottom. The edges of the guard lie on the same circle as the top of the cap. The blade itself conforms to the shape of the bottom of the cap. The blade’s edges seem to lie on the line connecting the cap edge with the guard edge.


How to find the “correct” blade angle

It is often stated that a good blade angle to start out with is about 30 degrees (relative to the skin). In order to find the corresponding handle orientation, it is recommended to place the top of the razor against the cheek with the handle being perpendicular to the surface of the skin, then lowering the handle until the blade just touches the skin. See the following diagram:





Note that for this razor’s geometry, that angle can also be obtained by placing the guard against the cheek with the handle pointing to the floor, then raising it until the blade touches the skin. This is because the edges of the guard, the top cap, and the blade all lie roughly on the same line. See the following diagram:





Warning: this approach is only valid if not too much pressure is applied to the skin. If that is the case, depressions are formed, and all bets are off.


The stroke

Now let’s examine what happens during a "perfect" stroke. When both the cap and guard edges touch the skin, the blade is also in contact and will cut whiskers very close to the skin.





Obviously, the razor was designed precisely so that the blade edge just touches the skin. If the handle is held such that either only the guard edge or only the cap edge touches the skin, the blade is lifted away from the skin. In this case, the shave won’t be very close. That’s why it is so important to figure out the curvature of one’s face, so that the handle can be oriented properly. This is very difficult to achieve consistently, so don’t despair too much, help is on the way.


How to overcome the difficulties of maintaining proper curvature

Essentially three options are available for the DE shaver (please let me know if there are others):

1. Apply pressure. Using more pressure allows the blade to cut the skin at other angles than those defined by the razor geometry. This method is difficult to master, however, we all use it occasionally, albeit perhaps involuntarily. Often, irritations, nicks or cuts are the result.

2. Use a Slant. Depicting blade-angle aspects for the Slant is an assignment for long winter nights...

3. Use adjustable razors (see following discussion).


The adjustable razor

For adjustable razors, the distance (along the handle axis) between the guard and the blade can be varied. I don’t know all adjustables on the market, but I surmise that the geometry of the razor at the lowest setting corresponds to that of a regular, non-adjustable razor as described above. When the distance is increased, there are now two options available for the handle orientation.

Orientation 1: In this orientation, the top cap is in contact with the skin, and the blade angle (with respect to the skin) can vary from about 30 degrees to somewhat larger numbers.





Orientation 2: In this orientation, the guard is in contact with the skin, and the blade angle (with respect to the skin) can vary from large values (about 60 degrees) to about 30 degrees.





The larger angles result in a more aggressive disposition of the blade. Therefore, using the top cap as a guide is safer than using the guard as a guide. However, I am convinced that many gents instinctively place the guard against the skin and then vary the angle, rather than using the top as a guide. I am saying that, because that’s what I did until I looked into things, and I don’t want to believe that I am the only one making this “mistake”. :biggrin:

Thus, using an adjustable razor at settings other than the lowest one, will likely result in closer shaves, but also in more irritations and perhaps more nicks and cuts because of the steeper blade angles.


What about the blade being parallel to the skin?

It is sometimes assumed that a parallel orientation of the blade (with respect to the skin) would be optimal. However, no DE or SE razor that I know of actually allows the blade to come close to the skin when it is held parallel.





The top cap will touch the skin first, resulting in a large gap between the skin and the blade. I am afraid, the ideal of a parallel blade is an exclusive of the straight-razor world. I'd be interested to know if there are any DE or SE razors that allow a parallel blade orientation.

That’s the end of my essay for this moment. As usual, if there are any factual errors, please let me know, and I'll correct them as soon as I can. Also, please let me know about any additions.

Best - MM
 
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Thanks for the illustrations, it must have taken some time. :thumbup1: Unless you are an illustrator pro. The only thing missing to this thread is a video to help visualize this angle problem.
 
Orientation 2 seems like looking for trouble - is it just me?
This morning, I had the biggest shaving accident ever! I took a big chunk of about 4 squaremillimeter right off my chin.

What had happened?

I had drawn the above illustrations about an adjustable razor using my Futur as a model. For the wide-gap illustration, I set it to 6 (the largest possible gap). After I was done, I put the razor back. This morning then, the accident happened. I had forgotten to turn the Futur back to my usual setting of 2.5!

I guess, I'll make a pre-flight checklist...

Best - MM
 
Eeeekkk :eek: it hurts even if I'm only reading it.

Something like that happened to me but luckily no gruesome accidents... because I usually prep the razor after the last shave, so I can pick it up and start right away.
 
The top cap will touch the skin first, resulting in a large gap between the skin and the blade. I am afraid, the ideal of a parallel blade is an exclusive of the straight-razor world. I'd be interested to know if there are any DE or SE razors that allow a parallel blade orientation.
An excellent article and drawings! Thanks for the efforts!

I have used a J1 Schick injector several times in the last month since I got it. It would seem that it allows the blade to get pretty close to parallel when the flat part is in contact with the skin. I do note that it shaves much more like a str8. It will get my cheeks pretty close to BBS in one WTG pass, and you have to be vewwy, vewwy cawwfull with it! :w00t:
 
That is the point of the illustration. Best - MM
While shaving today one idea hit my mind: for some mild razor, orientation 2 could actually be the only possible cutting position, as the gap is so small that the safety bar is always in contact with the skin no matter what.
 
Merkur HD: Blade & Handle Angles
I am more of a visual person, hope these help some people. I always thought it was odd to give proper blade angle, since a person can't see the blade. So I included both blade and handle angle. Let me know if I am off on my angles, I always forget to correct for pi.

I was under the impression that DE razors worked best when the blade was parallel to the skin, but I guess mozart showed me that this is not the case. I had to see for myself though. As for straight razor's being used at parallel angle, I highly doubted now that I looked at this images.

Ofcourse disclaimer applies: every razor is different, these are only approximations, my macro lens is on loan to a friend so I used a 400mm lens instead (hence images could be better, sorry), I am not trying to steal anyone thunder only trying to add to Mozart's work.
 

Attachments

While shaving today one idea hit my mind: for some mild razor, orientation 2 could actually be the only possible cutting position, as the gap is so small that the safety bar is always in contact with the skin no matter what.
In other words, this is the "normal geometry" case, where (as drawn above) any slight variation in the angle of the handle will cause the head or the bar to lift the edge away from the skin. It seems to me this might be a way to quantify the "aggressiveness" of a razor. A quick look at my 12C (barberpole open comb) shows that about 2-3 degrees either side of ideal will cause the blade to lift (eyeball angle measurements!). In other words, there's only about a 4 to 6 degree range of handle angles that will allow the edge to touch the skin. Zero is the mildest possible, and it moves up from there. A str8 would have 75 degrees or so. (At the high end, the top of the wedge will lift the edge away; and on the low end, once the blade passes through the horizontal, it can't cut even though still in contact.)
 
Merkur HD: Blade & Handle Angles
I am more of a visual person, hope these help some people. I always thought it was odd to give proper blade angle, since a person can't see the blade. So I included both blade and handle angle. Let me know if I am off on my angles, I always forget to correct for pi.

I was under the impression that DE razors worked best when the blade was parallel to the skin, but I guess mozart showed me that this is not the case. I had to see for myself though. As for straight razor's being used at parallel angle, I highly doubted now that I looked at this images.

Ofcourse disclaimer applies: every razor is different, these are only approximations, my macro lens is on loan to a friend so I used a 400mm lens instead (hence images could be better, sorry), I am not trying to steal anyone thunder only trying to add to Mozart's work.
I believe you are correct that the angle should be as close to parallel as possible. However, all of the above illustrations neglect the elasticity and flexibility of skin. The guard with a small gap plays an important part in keeping the whiskers from climbing the blade when shaving ATG. With a larger gap, more skin can be pushed ahead of the blade and cause burn and nicks, but can be tolerated when shaving WTG.
 
I believe you are correct that the angle should be as close to parallel as possible. However, all of the above illustrations neglect the elasticity and flexibility of skin. The guard with a small gap plays an important part in keeping the whiskers from climbing the blade when shaving ATG. With a larger gap, more skin can be pushed ahead of the blade and cause burn and nicks, but can be tolerated when shaving WTG.
Yes, the illustrations do neglect putting pressure on the skin/flesh. I did mention this in my original post as a potential means of overcoming the "limitations" of a razor.

Best - MM
 
I am not trying to steal anyone thunder ...
Not at all! Those are beautiful pictures and drawings. And more quantitative than mine. I was thinking about making pictures myself, but was too lazy, uh, busy in the end. Leisureguy should put all this into his book.

Best - MM
 
excellent diagrams! I've always thought the 'try to keep the blade parallel to your skin' comments were a bit odd, and this illustrates that point.
 
excellent diagrams! I've always thought the 'try to keep the blade parallel to your skin' comments were a bit odd, and this illustrates that point.
Yes, it's amazing how that piece of so obviously incorrect lore became so widely believed. The best str8 shavers say the optimum angle between blade and skin is about 30 degrees, which is pretty close to what the "normal geometry" drawing and the pictures show.
 
Yes, it's amazing how that piece of so obviously incorrect lore became so widely believed. The best str8 shavers say the optimum angle between blade and skin is about 30 degrees, which is pretty close to what the "normal geometry" drawing and the pictures show.
Sounds like we are saying the same thing. When I say as close to parallel as possible I mean the correct angle which in the illustration is somewhere in the neighbor hood of 30 degrees of blade to skin angle as opposed to the over corrected angle which is working from the opposite end of the cutting window.
 
Yes, it's amazing how that piece of so obviously incorrect lore became so widely believed. The best str8 shavers say the optimum angle between blade and skin is about 30 degrees, which is pretty close to what the "normal geometry" drawing and the pictures show.
I guess it would be difficult to devise a cutting implement that can cut both parallel and very close to a surface. For mowing the lawn, that's not a big deal, but for a beard where less than a tenth of a millimeter is already noticeable, the cutting edge would have to be impossibly close. One can cut hair only by aiming the edge at the skin (and trying to avoid cutting into it).

The way, a normal razor is constructed, a BBS shave should be achievable without applying pressure to the skin. Indeed, the technique of stretching the skin produces a "hard", relatively non-pliable surface (and it stands the hair up too). With that, one just has to make sure that the blade angle is correct, and - voila! - BBS.

Unfortunately, that's more difficult than it sounds.

How it all makes sense when one starts thinking about it...

Best - MM
 
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