Cap And Guard Mechanics And A Waxy Face

[mjclark]

Experimenting with guardless devettes, comparing Spitfire R41 cap to 2013 cap ground down to the same width, and experiencing the waxy face feel of the R41 and the G.B.S. bakelite razors has raised some questions for me:

1) How does the depth and convexity of the top cap of a DE affect the shave?
The Spitfire cap and a 2013 R41 cap ground down to the same 18.6mm width shave very differently although the guard bar is the same.
The Spitfire cap is shallower and less convex, but why does this make a difference to the end result even with steep angle (when it shouldn't come into play)?

2) With large blade gap razors, the guard bar seems to still be important but not to protect from the blade biting but rather to stretch the skin.
The guardless devette needs skin stretching to be smooth, but the R41 and some fierce bakelites are naturally smooth without this.

So how do the top cap and guard bar interact for the stretching effect?
And are toothcombs specifically designed to give the best skin stretching?

3) My two big toothcomb razors, the R41 and G.B.S. bakelite, both leave my skin feeling soft waxy and conditioned after the shave in a way that no other razors do.
It almost feels like the skin has been moisturised.
So what causes this effect?

I know some of you are deep into the mechanics and geometry of DE heads, so what do you think?

 

[DaltonGang]

I've never heard of this, and will be interested to her other views on this. I know different aftershave have this effect on me.
Then again, I've never shaved with a bakelite razor.

 

[shawnsel]

I was hoping that someone who has actually used an R41 would share their thoughts, but I'll take a stab at it from a purely-theoretical perspective:

1) How does the depth and convexity of the top cap of a DE affect the shave?
The Spitfire cap and a 2013 R41 cap ground down to the same 18.6mm width shave very differently although the guard bar is the same.
The Spitfire cap is shallower and less convex, but why does this make a difference to the end result even with steep angle (when it shouldn't come into play)?

My thoughts on top caps:

• A less convex top cap should create more blade exposure (as a more convex top cap would bend the blade's edge closer to the tangential line between top cap and guard).
• A more convex top cap will lessen the blade angle (relative to the skin), and pressure applied would be less directed towards the skin (but also possibly less efficient, skipping over more stubble)
• A thinner top cap should be less obstructive when shaving in tight spots like under the nose
• The bending of the blade in with the more convex top cap might also make the blade more rigid, dampening vibration and flexing of the edge (blade chatter)

2) With large blade gap razors, the guard bar seems to still be important but not to protect from the blade biting but rather to stretch the skin.
The guardless devette needs skin stretching to be smooth, but the R41 and some fierce bakelites are naturally smooth without this.

So how do the top cap and guard bar interact for the stretching effect?
And are toothcombs specifically designed to give the best skin stretching?

I think small blade gaps can act as a buffer to pressure by pressing down on the skin so close to the blade that they prevent the added pressure from (proportionately) getting the blade's edge closer to cutting skin.

I agree though that there likely is a point where especially large blade gaps might as well be devette's in regard to buffering from applied pressure. And I agree that the main thing a safety guard (solid or open comb) probably provides for razors with especially large blade gaps (or especially large blade exposure) is the stretching of the skin prior to the blade's cutting.

I've read here on B&B that the 2011 R41's teeth seemed comfortable and especially adept at guiding hair to the blade. That said, I've not tried an OC, and have never found a theory that I agreed with on why they would be significantly different compared to SB models with otherwise identical razor head geometries.

3) My two big toothcomb razors, the R41 and G.B.S. bakelite, both leave my skin feeling soft waxy and conditioned after the shave in a way that no other razors do.
It almost feels like the skin has been moisturised.
So what causes this effect?

This one has me confused. If you shave at a steep angle (pivoting on the safety guard/teeth), and the blade actually hovers above the skin, then I could see teeth with wider gaps potentially leaving more soap/cream/oil left behind on the skin. Other than that though ... I have no theories on this one....



Also, I've put together some photo illustrations of razor head angles and measurements that help me when I'm contemplating these things:

Negative blade exposure:
https://docs.google.com/drawings/d/1zWxr-Dv5qMAU3-ufBzpk-IVe9UXc_mpp_tnnKYlR_cw


Positive blade exposure:
https://docs.google.com/drawings/d/1IdsYtr8jnHJzZaUXW6gBx18E7AIhb55qrgvvIYhjyV4


Shallow blade angle:
https://docs.google.com/drawings/d/1JlnBPG0XqJ22p2fBVEwoJqHQw2BRA4teoo5vYGOoqnQ


Steep blade angle:
https://docs.google.com/drawings/d/1LqGWjYCNImtocNp-5eTktLwJvf7oCjxCQFHFBYkAEVo


Blade gap (really just an easier-to-measure influencer of guard span, I think):
https://docs.google.com/drawings/d/1NyTv43K7AEntXvfkPitz8YLyjzovOJe5O4Gns0HJWZA


Guard span:
https://docs.google.com/drawings/d/1WXnd0VrZVx2ws8wHhqliYuvvNiAzqIQyH9v5dvmfU1Y


Cap span:
https://docs.google.com/drawings/d/1fcStr2bFUhrXckJwOgqp74VXTsmdLfv56cJ2R5wTHjA

 

[mjclark]

Thanks shawnsel! That is a superb and intelligent post you made, and very helpful.

 

[shawnsel]

Thanks shawnsel! That is a superb and intelligent post you made, and very helpful.

Glad you liked it! I'm happy to have an opportunity to bounce these ideas off of others. Hopefully others will chime in and add more ideas.

Cheers,
Shawn