The Rain in Spain and the Shave Plane

The shave plane is a simple concept related to the very fundamental raison d'etra for the safety razor. The safety razor is based on the idea that a shave will be safer when you place the cutting edge between to fixed points that limit the blade's ability to cut deeply. So the top cap and the safety bar/guard are those fixed points. Those fixed "points" (actually lines) determine the shave plane.

Where the blade edge is in relationship to the shave plane determines the "safety," the shave character of the razor. If the edge lies under the shave plane, within the cove of the top cap and safety bar, the razor is "safer," more mild, less aggressive. Conversely, if the edge is above the shave plane, outside the cove of the top cap and safety bar, the razor is less safe, more aggressive, less mild.

In basic concept, the shave plane would be against the face, when shaving. In practice, this is certainly true for a mild razor with negative blade exposure, and often true for a razor with neutral blade exposure. For the aggressive, positive-exposure razors, holding the shave plane against the skin would start to peel one's hide like sod is removed and rolled prior to transport to a new lawn. This, clearly, is undesirable; so most users of uber-aggressive DE razors don't actually use a razor's shave plane, and instead, free-form the razor's shaving orientation against the skin by holding the safety bar off the skin to some degree while shaving.

The blade-bar span is measured (as much as possible) along the shave plane. (If the blade exposure is neutral, the span is measured exactly along the shave plane. If the blade exposure is positive or negative, the span is measured near the shave plane.)

The blade angle is measured in relation to the shave plane. In adjustable razors, where the safety bar can be adjusted up or down in relation to the blade fixed in the top cap, the gap and related span are the obvious primary adjustment. However, because the blade angle is measured in relation to the shave plane, by moving the relative positions of the top cap and safety bar, the orientation of the shave plane changes, thus making the blade angle variable as well. There are no exceptions to this fact for all adjustable DE razors that move either the blade-top-cap assembly or the safety bars to achieve adjustability. This certainly includes the Merkur Progress and the Gillette adjustables.

Likewise, the blade exposure is also varied as the shave plane changes in an adjustable. If the reason for this is not clear, please comment or email, and I'll elaborate in another article. (This morning, I have limited time for further discussion.)

Hope that helps to convey a fundamental of razor design and geometry.

Oh, and the rain in Spain is 1) wet, and, I hear, 2) falls mainly on the plain.  ;-)

Happy shaving!