The Razor Technician: Checking a Top Cap for Dimensional Uniformity

Some time ago I posted an article on how to check a new razor for safe use. It involved ensuring that the razor held the blade edges straight and uniformly exposed.

Since then I've had come up against a couple of situations that suggest further verification of the "trueness," the uniformity, the correctness of a given razor's condition. As a result of these situations, one of my concerns with a three-piece razor is the whether the key edges of the top cap are straight, parallel, and properly aligned with the baseplate.

The specific top-cap characteristics to be tested are as follows:

Test one: sight along an edge to determine straightness.

1. Are the long edges of the top cap (that lie above the blade edge) straight?
2. Are the long edges of the top cap in the same plane?
3. Are the long edges of the top cap parallel?
4. Is the plane of the top-cap edges parallel to the plane of the baseplate?

The first two tests, addressing numbers one and two above, are performed similarly to the way a wood worker checks the straightness of a board both for bow and twist.

Test one simply requires that the examiner sights along the particular long edge being inspected. That is, in the same way a carpenter will sight down the long dimension of a board to see if it is bowed, one would hold the top cap a foot or so from his face and "point" the edge of the razor top cap at his eye to detect any deviation from a straight line.

Test two: sight across the edges of the top cap to see if they
are in the same plane.

Test two is to sight across the edges to confirm that they align. To do this, hold the inverted (threaded rod up) top cap again about a foot from your face. Orient the top cap so that its long edges are parallel to a line determined by your eyes; that is, instead of looking down an edge as in test one, you will be looking across both edges. Arrange the top cap in your view so that the near edge aligns with the far edge in your line of sight. If the edges are in the same plane as they should be, you should be able to orient the top cap so that the edges appear to be parallel as you look across them. To see this clearly, you may have to choose the background and lighting carefully so that the edges are clearly illuminated and contrast against the background. I did this test near a window for good light, and held the top cap down over a dark table, allowing the light from the window to reflect up off the edges to my eye, while having the dark table as a contrasting background color.

Perhaps an easier test two is to simply put a blade onto the inverted top cap. If the (unflexed and presumed-flat) blade settles evenly onto both edges of the top cap without any gaps along the edge, that would indicate that the edges are in the same plane.

If test one confirms that the edges are straight, and test two confirms that the edges lie in the same plane, then test three is using a micrometer to measure the distance between the top-cap edges (that is, the width of the top cap from edge to edge). If the edges are uniformly equidistant as well as in the same plane, then they are parallel.

Test four is a bit tricky because it requires a baseplate that is not twisted and a top cap with a sufficiently-long threaded rod to allow the top cap to "float" as described below. To check the baseplate for twist, put it, inverted, on a known flat surface and seeing if the baseplate rocks. (It shouldn't.) A second check would be similar to test two, above, where one sights along the plane or upper surfaces of the baseplate to see that they are generally flat and parallel. If these conditions don't exist, or if the threaded rod isn't sufficiently long, then you can't perform test four.

Test four: adjust the "tightness" of the top-cap screw so that
the threads support the top cap and allow it to "float" just
above the flat razor blade.

To do test four, one would assemble the razor including a blade. However, don't tighten the baseplate snug against the top cap. Instead, once the top cap has been threaded onto the top cap a bit, hold the razor upright -- that is, with the top cap up and the handle down. Then adjust the degree to which the handle is threaded so that, with the baseplate supported by the handle, the threaded rod in the top cap is screwed into the handle so that the top cap is "floating" above the baseplate and just touching the unbent blade. Ideally, the top cap would be uniformly just touching or just above the unbent blade. If the top cap is askew, then either its functional plane isn't perpendicular to its threaded rod, or the threaded rod is too short or threads too imprecise to give an accurate indication of the top cap's condition.

If the threaded rod is too short to allow the completion of test four, then the safety tests in my earlier article on inspecting a new razor should be sufficient to complete the inspection of the entire razor and the top cap specifically.

These are the tests to determine if the top cap of your two- or three-piece razor is "in shape" properly hold a DE blade against the baseplate for a safe shave.

Happy shaving!