Thread: Angle of Attack

Ok, now what's he yakking about, right??

Think of a guillotine. In fact do a Google search if you are not familiar with one. Basically it is a device with an angled blade that drops straight down and slices through, ummmm, stuff.

Imagine if the blade was, instead of angled, placed straight across so that when it dropped on, stuff, it impacted with it's full length all at once. Instead of slicing through stuff, it would tend to crush, stuff.

That blade angle is the key to quickly and cleanly slicing, stuff. Note that the blade travels in a single plane of motion, straight down. There is no lateral movement, no forward nor backward side to side plane of movement. The angle of the blade does all the work.

This is exactly how a straight razor works to cleanly slice through stuff, like beard hairs. If the blade meets the hair head on, it will effectively try to crush through instead of slice through. Read: pulling and irritation.

The trick, as you move the razor around the different angles of your face, is to maintain that crucial angle of the blade where it meets/attacks your beard.

The other trick is to hold that single plane of movement so that the blade never, and I repeat NEVER, travels in a tangential or parallel plane to the skin.

Good luck,

Scott

The only problem with your theory is that if it was true you couldn't do the Hanging hair test. The hair meeting the edge of the razor straight on would then crush the hair and not cut it unless you presented it at an angle.

Just thought I'd throw a fly in your ointment!

Scott,

Do I understand this concept to mean that instead of a straight n-s pass, we should move the blade in a kind of n-sw or mild sweeping motion?

Think snowplow blade.

Ok, let me restate this part. The broad plane of the blade does in fact move tangiential to the plane of the skin, but...

Consider the point of the razor a reference point.

The point never moves forward nor behind the plane of motion as the razor travels over the face.

Hopefully that is more clear.

Scott

PS - bigspender, I'll address your pesky 'lil fly later. I'm at work stealing just a moment to clarify the above, but I gotta go!

Scott,

I think I agree with what you're saying about the angle, but I'm not sure about one part of it.

First off, using the blade with an angle makes a huge difference. For me, either angling the toe of the blade downward for the N-S strokes, or else using a slight toe-leading motion on the stroke makes it cut through the tough beard on my chin a lot easier.

I'm not sure about the "crushing" you talk about, though. If you watch the National Geographic shaving video, they talk about a razor being so sharp that it just slides between the hair molecules. So regardless of whether or not it slices at an angle, you're breaking molecular bonds, not tearing them apart like a less fine edge would do.

I think analogies to a knife blade or guillotine break down for that reason. I think a knife rips molecules apart. A razor almost nudges them aside.

What does this mean? I'm not sure. I agree with your observation, but I have some questions about why it's true. Maybe the angle helps a less sharp razor keep cutting.

Anyway, not trying to pick a fight. I'm enjoying your "lessons" lately.

Respectfully,
Josh

That's why 'smiling' blades shave so great...you're always presenting a curved edge to the area being cut, which effectively presents a side-to-side sawing cut without actually moving the blade side to side (on a microscopic scale, of course).

Originally Posted by joshearl

I'm not sure about the "crushing" you talk about, though. If you watch the National Geographic shaving video, they talk about a razor being so sharp that it just slides between the hair molecules. So regardless of whether or not it slices at an angle, you're breaking molecular bonds, not tearing them apart like a less fine edge would do.

Edit: the following is wrong - human hair is made of keratin, not collagen. Perils of posting under the influence. The truth, however, is even worse for the "sliding between molecules" theory. See the followup post.

Human hair is made of collagen. The basic collagen molecule is 300nm long and 1.5nm thick - basically a microscopic rope. Since a micron is 1000nm, this means the molecules are roughly 1/3 micron long.

Compare that to the grits we use for shaving. We can pop hair with a 6 micron hone. Obviously the fin is thinner than the grit size, but it seems unlikely that an edge that coarse is somehow missing the main body of these "ropes" and instead slides between the ends of adjacent "ropes" that are twisted together to make up a hair. It seems more likely that it really does tear these "ropes" as it cuts, or possibly just catches the molecules in front of the fin and pulls the hair in two, or some combination of the two.

mparker,

The video also shows the hair bending slightly before it starts to cut. Could the razor blade be sliding along the body of the collagen molecule until it finds the end, then sliding in?

It seems unlikely to me that the blade could then thread its way between molecules with the measurements you're giving. Maybe National Geographic was oversimplifying?

Just trying to fit the pieces together...
Josh

NG was oversimplifying. Three collagen molecules (which are already pretty large compared to the fin of the blade) are twisted into longer fibrils. These molecules are staggered within the fibril, and as one collagen molecule ends another takes it's place (so a fibril may contain thousands of collagen molecules, but only three at any given place). If a collagen molecule is a short cord, a fibril is a very long rope. These fibrils are arranged differently for hair, cartilage, corneal lenses, and all the other stuff that collagen is used to build in the body. But for hair they're bundled together and twisted like a giant cable.

(I can't believe I'm about to use that wikipedia as a reference)

http://en.wikipedia.org/wiki/Collagen