Wednesday, May 21, 2014

Potential Causes of a Poor Shave, Part Four: Seven Key Aspects Razor Design

Today's article delves into the aspects of razor design as well as blade-razor combinations, the last two items on the list below:
  1. Razor-blade edge that is not straight due to razor defect
  2. Rough surfaces on the razor due to defect/damage
  3. Incorrect blade position in razor head
  4. Excess pressure of razor on skin
  5. Excess speed of shaving strokes
  6. Shaving multiple planes of the face in single strokes
  7. Shaving in the wrong direction in sensitive-skin areas
  8. Too many strokes in the same area
  9. Insufficient prep and lather
  10. Dull blade
  11. Mismatched razor design (blade angle, reveal, exposure, gap, and more) to skin sensitivity and hair toughness
  12. Mismatched combination of blade, razor, and skin
Although the preceding list mentions four major razor-design characteristics, there are at least seven to consider. In addition to the four already mentioned in the list (blade angle, reveal, exposure, and gap), I must add blade-stiffening ability of the razor, its safety bar design, and the slant of the edge -- that is, straight (edge perpendicular to the handle), or slant (and degree of slant), which is the salient aspect of a slant-bar razor. 
Each razor has ten design aspects that can affect quality of shave. Combine that with blade characteristics and skin and hair variables, and the combinations and the potential outcomes can be dizzying!
Left to right: Merkur 37C slant, Gillette adjustable, Weishi 9306-f, Wilkinson Sword Classic, and Merkur 33C.

In addition to those seven, there are other design characteristics that many feel are important including razor weight, handle dimensions, and razor balance. Because I feel these are fairly well understood by all DE users -- and important to some, not to others (I, personally, care little about handle length or razor balance, and ultra-light razors can be an issue, but otherwise I don't much care), I will simply assume that you take them into account when considering a razor design and the quality of your shave experience.

As I often do, I would like to pause the discussion and address vocabulary so that you and I start with a common understanding. 

For the purposes of this discussion, blade angle refers to the angle measured along the line of shaving direction, in relation to the razor's top cap and safety bar. 

To elaborate on this, if you think of the edge of the top cap, which is a line, and the safety bar, which in a straight-bar DE represents a second line parallel to the edge of the cap, generally speaking these two parallel lines determine the shaving plane of the razor head. The more perpendicular the blade is to this shaving plane (when viewed along the non-cutting edge), the more more harsh the scrape of the blade edge against skin.
Contrast different (exaggerated) blade angles:
Left is smaller angle (less harsh), right is
larger angle (more harsh).

So larger blade angle would generally have the blade bent less under the cap and would be closer to the cross stroke on a letter T (when viewed in cross section, that is, from the dull edge of the blade), while a smaller blade angle would require the blade be more curved under the razor's top cap, and could be thought of as looking in cross section like a letter T that has more drooping cross stroke. All other things equal, a small blade angle would be considered less harsh, more slicing, less scraping, of the hair, and a larger blade angle less cutting, more scraping (so therefore might be more irritating to the skin).

Blade exposure describes how well the cap and safety bar protect the skin from the blade edge. A larger, positive, exposure suggests the edge is more exposed, not protected by the top cap and safety bar -- more aggressive and, therefore, potentially more harsh, more threatening; a smaller, negative, exposure implies that the edge is more retracted into the cove of the top cap and safety bar, and therefore less aggressive and less likely to bite. 

Smaller blade reveal (left) compared to larger (right).
Blade reveal describes how much of the blade is visible from the edge of the top cap irrespective of position in relation to the safety bar. Greater reveal gives more opportunity for micro-vibrations of the edge, potentially contributing to a more harsh shave.

Razor gap means the space between the blade edge and the safety bar. Larger gaps offer a more aggressive cut; smaller gaps would make a less-aggressive razor. 

A stiff blade (as influenced by razor design and not the blade itself), would be secured in the razor in such a way to offer less opportunity for edge vibration as one shaves. The razor can influence blade stiffness by limiting the blade reveal (as already mentioned), by the degree and nature of the blade curvature, by the material of the razor head (for example, plastic may damp vibration better than metal), and by how the blade is secured into shaving position (that is, the amount and location of blade-clamping contact within the shaving head). This last factor can be appreciated if one thinks in terms of extremes: a blade in solid contact with both cap and baseplate for the entire area under the top cap would be a low-vibration design. A blade that is curved by contacting only on top the long edges of the cap and underneath by a single center strip of the baseplate (this is a hypothetical design only), this would likely be a high-vibration design. Less vibration means a more comfortable, irritation-free shave.

The safety bar limits the blade contact with the skin. There are different safety-bar designs from nearly round cross section to open comb. Safety bars may have less effect on harshness and more on long-hair cutting ability. Open-comb bars tend to let many longer whiskers better direct access to the blade, and may also allow more lather on the skin while the edge is actually cutting hairs. Scalloped cuts in the safety bar also may allow lather to better cushion the shave, but, like less-grooved safety bars, may press longer whiskers down, away from the blade, making the pass less effective.

A slant-bar razor not only curves the blade from edge to edge;
it twists it too. This puts both edges on a slant
in relation to the handle.
Edge slant distinguishes a straight-bar razor, which is the vast majority of DE razors, from a slant-bar razor like the Merkur models 37 or 39 razors. With the slant bar, the edge slants in such a way that when the shaving stroke is made in the same direction as the handle, the edge is not perpendicular to stroke direction. A slanted blade is more efficient in its cut, making it cut more aggressively. 

The reason a slanted blade or an oblique slicing motion such as the so-called Gillette slide works better is less-well understood, however, by most persons. Yet the reason is simple: when a straight blade cuts obliquely, the functional angle of the cutting edge itself is essentially reduced, meaning that its effective sharpness is increased. It is simple geometry; let me explain further: 

If you picture the line that a pencil lead would trace as you cut it with any sharpened edge, a straight-on (perpendicular) cut would make a line up the blade that is perpendicular to the cutting edge. An oblique cut would make a line on the blade that is not perpendicular to the cutting edge -- it is, well, oblique. If you were to cleave the blade along those two pencil lines, you would see that the cross sections are different. The oblique-cut cross section has a longer, sharper point in comparison to the cross section cut that is perpendicular to the edge. This means that an oblique cutting angle makes any blade effectively sharper, more efficient in its work.

Another side benefit of the slant-bar design is that it may also tend to stiffen the blade, which may offset to some degree the potential harshness of its larger blade reveal. There are other subtleties to a slant-bar razor, but to cover them all would require its own article -- maybe on another day.

Let's review the more esoteric design aspects of a DE razor:
  • Blade angle in relation to the shaving plane of the razor head
  • Blade reveal describes how much of the blade is covered by the top cap of the razor.
  • Blade exposure is the degree to which the blade edge is held underneath the shaving plane of the cap and safety bar, within their protective embrace.
  • Razor gap is the distance between the blade edge and the safety bar.
  • Blade stiffness (as determined by the razor design, not the blade itself) affects blade vibration while shaving.
  • Edge slant is the degree that the blade edge deviates from square to the handle
  • Safety-bar design (round cross section, scalloped bar, or open comb) can affect how easily the blade can contact skin and how much lather remains as blade slices stubble.
Plus the three with which most are familiar:
  • Razor weight
  • Razor balance
  • Handle length & diameter
Many of these factors can compound or offset the effects of one another. For example, let's discuss generic TTO razors. I tend to believe that these razors have larger blade angles and, because of the butterfly-door design, may allow for more edge vibration than many two- and three-piece designs. Both of these factors would tend to make the TTOs offer a more harsh shave all other things equal. But when combined with smaller blade reveal and edge exposure, this would reduce the harshness of the shave. Further, if the razor gap is relatively small, this further increases the mildness of the shave. Also, most TTO razors have a stamped-metal safety bar that is not smooth along its length, but rather have a series of tiny grooves, like micro-scallops, that probably limit the likelihood of skin squeezing into the grooves and potentially nicked by the blade, but also likely allow a small amount of lubrication to remain on the skin as the safety bar slides ahead of the razor edge, and also limit the razor's ability to efficiently cut longer whiskers. In an adjustable TTO, such as my Gillette Slim, the safety bar can be adjusted to select the gap size that can compensate for the other design elements that are permanent. Therefore, to some degree, one can adjust the gap size to tune the aggressiveness (and potential harshness) of the razor to meet the user's needs.

Is this single gap adjustment adequate adequate to manage harshness and quality of shave? It depends. If one needs a more aggressive cut, this can be achieved by opening the gap, but one then is left to deal with, most notably, whatever is the inherent blade vibration of the design and the fixed blade angle, which may be more harsh than the user's skin needs; this can be a problem for those with more fragile skin. If the user is unaffected by a higher degree of blade scraping and edge vibration, then the TTO's adjustment feature is completely acceptable.

Blades, too, vary in their characteristics, which are primarily two: sharpness and durability. (Technically, we could add third and fourth characteristics of smoothness and innate stiffness of the edge, but these are heavily influenced by razor characteristics, and utterly impossible for the average person to evaluate without being influenced by razor characteristics.) A sharp blade may be ground and coated (or not) in such a way as to be more sharp or less so, and to be smoother or less so on a given face and hair type, and in a given razor. Durability is probably the result of blade material, microscopic details of the edge grind, type of hair being cut, and the care of the blade between shaves.

If your head isn't spinning too much, then you might appreciate why the DE shaving experience is so subjective. Take the seven primary characteristics of a razor, add the three others (weight, balance, and handle length), then include the blade characteristics, and finally factor in skin and hair differences -- this explains how easy it may be for a shave to be less than optimal (and we haven't even considered shave prep and product variables).

Yet as one balances the design factors, the shave can be close, comfortable, and rewarding for those moments in the day that he completes the shave ritual. And this is how I hope it goes for you.  Happy shaving!

Abbreviations:  DE = double edge;  TTO = twist to open

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