No pressure! Let the weight of the mower do the work.

[rajagra]

I was using a lawn mower analogy to explain an idea I had, and realised I could use it to explain the two theories:

• Let the weight of the razor do the work.
• No pressure.

Have you noticed that when you are pushing a lawnmower, you sometimes hit a bump or clump of grass, and the mower stalls?
This is because you are pushing along the axis of the handle. The force can be broken down into horizontal and vertical components.
The vertical force acts downwards, reinforcing the weight, making it hard to go over the bump.



So what do you do when stuck on a bump? You instinctively go into reverse. The mower moves more easily, because you are pulling.
The vertical force acts upwards, counteracting the weight.
You could continue moving backwards, making the whole job easier.
(Ignore the fact that you would normally take a run forward to attack the bump at this point!)



What does this have to do with shaving? Well when you allow the razor's weight to fall on the face, it is essentially the same as reversing that lawnmower.



If the razor tugs on a tough hair, this protects you. The perpendicular force you're exerting is away from the skin, so when the razor stalls, you pull it away from the face rather than digging it in, which would cause a cut.

In practice you aren't lying on your side! So you hold the handle loosely below the centre of gravity. The weight 'topples' the razor against your face.
You move your hand along a line parallel to your face. In this way you aren't actually pulling the razor away from the face - but neither are you pushing it down. You are truly exerting no pressure.

When you can't use the weight in this manner - e.g. shaving upwards - you simply apply a little torque (rotational force) to the handle. This pushes the razor head against your face, i.e. it applies some pressure as a substitute for the weight. But apart from that, you still move your hand parallel to the skin. Don't bear down consciously other than applying that torque. If the razor tugs, your movement will pull the razor away from the skin, preventing a cut.

Hope this makes sense!

 

[drmatt357]

This is all good but you have to realize that the gravity vector is PARALLEL to the skin, not perpendicular as in your grass cutting analogy. You MUST apply pressure to the skin with the razor in order for it to work.

 

[rajagra]

This is all good but you have to realize that the gravity vector is PARALLEL to the skin, not perpendicular as in your grass cutting analogy. You MUST apply pressure to the skin with the razor in order for it to work.

Ah - but you don't actively generate that pressure. It is reactive.
The centre of gravity of the razor is above and to the side of where you hold the razor. This creates its own torque, causing the razor to rotate and fall against the skin. There is force between the skin and razor (equal and opposite reaction.)
By limiting your hand to moving parallel to the skin, you will match that horizontal force.

So while your hand will provide that horizontal force, it is in response to forces that generate themselves.

In the picture below:

• Gravity creates weight, which pulls down on the razor at the centre of gravity;
• The hand pushes the razor up to counter gravity ('counterweight');
• Because those two forces are horizontally offset, this creates clockwise torque on the razor;
• But skin stops the razor rotating by generating sufficient force F against the razor;
• There is an equal and opposite reaction force, also F, pushing the razor against the skin: the effective pressure;
• To balance horizontal forces on the razor, the hand also generates horizontal force, again precisely equal to F.

The user does not need to think about pushing against the skin. Just maintain a fixed distance from the face and physics takes care of it for you.

 

[Wyokid]

Like it!

 

[TallyShave]

No pressure, light pressure, responsive pressure, active pressure, negative pressure, peer pressure...

Your face will tell you precisely how much pressure and of what variety to use. How we define or describe it is much less instructive.

 

[Viseguy]

Nice graphics. And I think you've put into words what an experienced wet shaver does intuitively, or at least strives for. In practice, your face isn't perfectly vertical or perfectly flat -- far from it -- so stuff occasionally happens.

 

[Craig_From_Cincy]

Great post Ray. It took me a long time to learn to let the weight of the razor do the work. Pushing down too hard caused me a lot of razor burn and more than a few weepers.

 

[drmatt357]

Ah - but you don't actively generate that pressure. It is reactive.
The centre of gravity of the razor is above and to the side of where you hold the razor. This creates its own torque, causing the razor to rotate and fall against the skin. There is force between the skin and razor (equal and opposite reaction.)
By limiting your hand to moving parallel to the skin, you will match that horizontal force.

So while your hand will provide that horizontal force, it is in response to forces that generate themselves.

In the picture below:

• Gravity creates weight, which pulls down on the razor at the centre of gravity;
• The hand pushes the razor up to counter gravity ('counterweight');
• Because those two forces are horizontally offset, this creates clockwise torque on the razor;
• But skin stops the razor rotating by generating sufficient force F against the razor;
• There is an equal and opposite reaction force, also F, pushing the razor against the skin: the effective pressure;
• To balance horizontal forces on the razor, the hand also generates horizontal force, again precisely equal to F.

The user does not need to think about pushing against the skin. Just maintain a fixed distance from the face and physics takes care of it for you.

View attachment 332938

Fair enough. As I can see from this schematic, about half the weight of the razor would be applied to the skin... BUT what about across the grain or even against the grain?
I still think you need to apply pressure against the skin. (Assuming you're upright and not lying on your side or on your head)

 

[mikey]

You should be holding the razor such that your thumbnail it at the center of gravity.

Thanks,
Mike

...View attachment 332938

 

[bcraig.waciii]

Oh the joys of reading from the great scientific minds of the experienced wetshavers, who in all reality could be some of the greatest shaving philosophers of our time. Carry on gentlemen!

 

[rxonmymind]

Too funny! This reminds me of a thread of less scientific approach....

http://badgerandblade.com/vb/showthread.php/290677-So-I-m-mowing-the-lawn-Lol?highlight=

 

[Emanon]

Now, I want a lawnmower that looks like a safety razor.

 

[76GTfan]

Reel or rotary mower. LOL

 

[Useless shaver]

Great discussion, gents!

(didn't get it though...)


Just kidding!

 

[mikeeliaspgh]

I have figured out how to do "no pressure" during my 3 passes... I have not figured it out during my clean up / buffing on chin - almost always give myself razor burn...

Ideas? Tips?

 

[rajagra]

The trouble with the chin is that it's rounded in two axes. It's tempting to apply pressure to flatten it.
Better to pull the skin up or down so it's flat in at least one direction.

 

[mjclark]

This is a very interesting thread and goes a long way to explaining why for some it's simply "the heavier the razor the better"- that would be for those who hold the handle near the base so that its weight is transferred to the head.
But for others it is more important to balance the handle and head weights- that would be for those who hold the handle closer to the head so that it counterbalances the head.
Even in this seemingly clear cut issue, it all depends on technique and hey, guess what?: YMMV

 

[talibeard]

Just don't forget to stand on your head for an ATG pass!!

 

[SilkySmooth]

That razor wont mow anything down unless you put a blade in it!

 

[DirtDiver]

I like this, I think it is a good illustrated explanation for the newbie wet shaver. I could have used it a couple months ago