Monday, March 9, 2015

The Challenges of Quantitative Analysis in Razor-Head Design

In turning my thoughts once again to understanding individual razor design -- and thereby, being able to better compare one razor to another -- the issue always comes back to a razor head's key measurable dimensions, that is, the big three: blade exposure, angle, and gap.

Of the big three design factors, the one that most drives shaving character of a razor head is blade exposure. Obviously, the more exposed the blade edge is in relation to the cove of the razor head's top cap and safety bar (or comb), the more aggressively the blade can attack whiskers (and face). However, I would suggest that exposure and gap together tend to be the primary factors that determine shave closeness. Similarly, exposure and angle are the primary factors that, together, determine comfort -- that is, the tendency of the razor to scrape and thereby irritate skin irrespective of wounds.

So in comparing the general shave characteristics of razors one to another, this can often be easily done qualitatively -- that is, without measurement -- when the differences in shave character, one razor to another, are very different. It can be much more difficult in some cases when the differences in razor shaving character are more similar. It seems obvious that measurements should be made.

Many are comfortable with measurements. They are concrete, definite. Something on which one can really hang his hat. Or are they?

I, myself, bought a small micrometer to make razor-head measurements. I even published some of those measurements in these blog articles (but with the warning that they are approximate). However, the reality is that no measurement is exact; there is always a level of uncertainty based on the accuracy of the measuring device, and, in the case of razor heads, the suitability of the measuring process to the dimension being measured. In plain language, I'm saying it's difficult to get reasonably-accurate measurements, in particular, of blade exposure and blade gap, because of the configuration of the razor and the dimensions being measured. It's hardly as simple as measuring the outside dimension of a pipe.

A micrometer is not well suited to measuring either gap or exposure directly. The problem with exposure is that one is attempting to measure the depth or height of the blade edge in relation to an imaginary shave plane; the shave plane is a real concept, but it doesn't exist physically, so it's difficult to use as a measurement end point. The blade gap, however, exists between two physical end points: the blade edge and the line along the safety bar (or comb) that determines the shave plane. The rub with this concept is that it's virtually impossible to use this safety-bar line as a hard end point for taking the micrometer measurement.

In practical terms, I don't trust my own measurements because I recognize the challenge of getting these physical dimensions. I also don't trust any else's measurements for the same reason. The only way I would trust stated dimensions is if the measurement methodology were explained in detail and also seemed likely to be fairly accurate. Dimensions from a razor merchant fall into this category: unreliable. However, dimensions supplied by a manufacturer are likely to be more trustworthy -- though there are no guarantees. For example, given the general level of deception in transactions with Chinese sellers and manufacturers, I wouldn't bet my life on dimensions provided from that group; they could be accurate in theory, but their razors too often aren't even consistent in as-delivered condition! A German manufacturer, at the opposite end of the spectrum, might be suspected to be more scrupulous -- though there are no guarantees, of course.

So how can one get direct measurements of a given razor or compare one razor's dimensions to another? Relative dimensions from photos can only be obtained when the same camera lens is the same distance from the razor. So it seems that if one places two razors side by side such that the nearest side of the blades are at the same distance from the camera lens as well as making the lens equidistant from each blade edge, a direct comparison could be made. However, absolute measurements wouldn't be accurate due to parallax effects -- due to the camera not looking directly down the edge of either razor blade.

When doing measurements off of photos of only one given razor and the lens is looking directly down the blade edge, the problem is degree of enlargement. This is affected by the camera lens itself and the distance of the lens from the near edge of the blade in the razor. What to do, what to do (accompanied by much wringing of hands)?

The answer is simple, but not easy (sigh).

The best way I can figure at the moment is to somehow mount an accurate ruler above the razor head and the same distance from the camera as the nearest point of the razor edge. Then take the side-view photo with the camera sighted directly down that razor edge. But, unfortunately, the pain doesn't stop here.

Then with a set of dividers (similar to a compass) one transfers the key dimensions from the photo and measures those with a micrometer. (The measurements might also be taken directly off the photo with the micrometer, though I suspect that using dividers properly might build in, not more accuracy, but quite possibly more consistency into the measurement process.) The key dimensions include not only blade exposure, gap, and angle, but also a measurement of a ruler dimension. This measurement of the ruler allows for a simple algebraic conversion to derive a factor so that the measurements off the photo can be converted to measurements in life's 1:1 scale.

Absent measurements taken with this kind of rigor, the best one can hope for is qualitative assessment of relative blade gaps, with a qualitative adjustment for the effects of blade gap and angle.

Happy shaving -- and razor-head analysis!

1 comment:

  1. I believe most blade gap measurements are taken with a feeler (aka thickness) gauge:

    While measures between two people/razors typically varies a bit, it does seem to be fairly accurate.To my knowledge the largest list of hobbyist-measured blade gaps is here:

    Blade exposure (as you say above, the much more influential aspect of razor aggressiveness) though is a different story. To date I have yet to see any reported blade exposure measurements ... except from a couple manufacturers who share them from their design specs (and of course the actual razors may vary slightly from the original design specs).

    Blade exposures are *extremely* small though. There is a vintage "New Salesman Training Manual" from Gillette, which illustrates their adjustable razor going from mild to aggressive through adjusting the blade exposure by just 0.2 millimeters (and also a corresponding 10 degree difference in the steep shaving angle). (note: I'm assuming the measures on the diagram are quoted in inches, but here I've converted to millimeters)
    (note: viewing images from B&B requires a (free) login)