Bevel-setting in theory and practice
For sharpening razors with the use of flat hones, establishing a proper bevel shape early in the sharpening process is an absolute condition for success. Failure to meet that requirement is one of the most common honing mistakes, and although it is not very difficult, many straight razor users that wish to sharpen their own razors struggle with this aspect of the process. The main reason for this, is because a cutting bevel can take different incarnations. Sharpness is only limited to how cleanly both side of a blade can meet each other and the angle at which they join. In theory it does not matter if those sides are flat, convex, concave, or even irregular, as long as the apex is one clean line, as thin as possible. But in our real world practice, we use flat abrasive tools, and those tools are only effective with flat bevel sides that lay in the same field as the imaginary field that touches the spine and the edge. In other words: flat bevels in a fixed angle are mandatory for successful sharpening on hones.
Shaping the bevel can require a substantial amount of steel removal. It is imperative to achieve this goal with a hone that is up to the task.
Let’s look at a drawing that represents the most common possibilities.
Types of bevels
The blue parts show the soonest reachable good bevel shapes. The black part shows the amount of steel that needs to be removed.
The convex bevel
This is a frequently found bevel shape on razors. Usually this is the result of frequent stropping on abrasive pastes. As such this is a valid option for getting a keen edge, but once the decision has been made to (re)sharpen with hones, the bevel needs to be brought in its flat state again. It is clear that this can require the removal of a fair amount of steel.
A convex bevel is not easy to spot. Visual inspection, whether magnified or not, is not very reliable for detecting convexity. The way light reflects off the bevel panes can reveal something, but it is difficult to be certain. The magic marker test is a better choice of unmasking convex bevels. Another problem with convex bevels, is that the keenness often is still more than adequate to allow the razor to pass the Thumbnail test, which makes it impossible to tell when the last trace of convexity is cleared. The “downstroke”-technique can be used to circumvent this issue. (read below about the downstroke technique.)
The divergent bevel
There are various reasons why divergent angles may be present at the bevel. Some are fully intended, for instance when a razor was previously honed with a layer of tape attached to the spine. This is a perfectly sound method to prevent hone wear at the spine of a razor. If the divergent angle is known, in other words, if you know how much tape to add, the razor can be honed as such. Otherwise, the bevel needs to be completely reset. This can be done with, or without tape, depending on personal preference on this matter.
When it is unsure whether the bevel has the desired angle, the magic marker test holds the answer.
A second reason for a divergent bevel is the creation of a secondary microbevel, which is a honing method derived form the way chisels and various woodworking tools are often sharpened. It depends on how much honing was done with the changed angle, where the split point can be found between the original and the new angle. The split point can easily be spotted with visual inspection at magnification.
A third diverging angle can sometimes be found on new razors. One method to cut the initial bevel panes, at the factory, uses a spinning abrasive disk. To prevent wear on a new product, the spine is raised above the surface a bit. Needless to say this induces odd bevel angles, that need correction during the first honing of a razor.
As with the convex bevel, in all these cases, the sharpness tests may yield false readings, left by the residual keenness from the old edge.
The dull bevel
This bevel has a rounded apex. It is dull, from prolonged use, or from cutting other material than what the razor is designed to do. This condition is very often found on old, abandoned razors. It can't be seen with visual inspection, nor with the magic marker test. Luckily, the thumbnail test will give us a clear reading that the razor is not performing well.
The microchipped bevel
This is in fact more an edge condition than a bevel condition. The cause can be razor abuse, but also too much work on hones that are prone to cause chipping / wire edges. Visual inspection under magnification is the only way to positively identify this condition. If the missing chips are big enough, the thumbnail test might also reveal something. Again, the downstroking technique might come in handy to deal with this situation and subsequently reestablish a good bevel.
The following diagram shows which tests are useful to detect the various bevel conditions.
Usability of the available tests
- For more information about the tests: Sharpness tests explained
The downstroking technique
One of the major challenges in establishing a good bevel, is to know when the goal is reached. On condition 3, the dull bevel, this is fairly straightforward. Bevel formation is finished as soon as the entire length of the edge passes the thumbnail test or the shave arm hair test. The thumb pad test also can be used, but this test is more demanding of skillful interpretation.
With conditions 1,2 and 4 things are more complicated. The edge may yield false readings on all those tests. Experienced honers have a fair idea of the bevel condition, upon rehoning their own razors. They know if they should expect a degree of convexing, and the approximate amount of work it’ll take. For those that have no idea what kind of work to expect, dulling the edge just enough to loose all ambiguous readings greatly simplifies the plan of action. Once the razor starts out, even barely, dull enough to duck the tests, we only need to work on a bevel-setting hone, till it passes the tests, as described above.
The easiest and gentlest way to dull a razor is to put it with the edge down on a glass jar and perform one, maybe two, cutting strokes without any significant pressure.
The technique can also be adapted to remove microchips. In that case the razor can be downstroked at the side of a very fine hone, till all the chips are gone. This calls for some sort of magnification device to inspect the edge.
Choose your weapons
Establishing a good bevel might ask for the removal of a decent amount of steel. Luckily, this is something that not needs to be done often. Usually only for a first time honing, on a new razor or a restored one, or if we change the honing angle from taped to tapeless. But, and this can’t be emphasized enough, what needs to be done, needs to be done. A coarser hone removes steel more rapidly than a finer hone. We must not be afraid to use one, as long as we make sure to remove all coarse scratches on the next level. Coarse scratches that are neglected can turn up as small chips at the edge, during the finer honing stages. (this is one of the causes for the dreaded "overhoning") As a rule of thumb, scratches can only be effectively removed during the next honing step.
Ideally ,the bevel should be completely formed by the time we traverse the 2K mark. After that it becomes increasingly more difficult and time consuming to achieve our goals. Fail at this level and the subsequent hones will put a nice polish on the faces of your incomplete bevel, but do nothing for the actual edge of that bevel, simply because it does not really exist yet.
A good strategy for when you need to do extensive bevel work, is to start out on a 600 grit stone, and move to 1000 or 1200 as soon as parts of the edge starts to respond to the thumbnail test. There’s still plenty of work to do now, in order to remove all 600 grit scratches, before you’ll complete the 1K stage. Stay on it till the razor shaves arm hair with great ease and passes the thumbnail test along its entire length. Finalize your work with a number of ultra light laps on the same hone, or on a 2K hone if present. Don't use the thumbnail test after that, as it holds a risk to dull the edge somewhat.
Watch your defense
Some like to shield the spine from the hone, by adding a layer of tape. In general, electrical insulation tape works best for this. As explained above, the application of tape also alters the honing angle, so you need to keep record of it. Once a razor is honed with tape, it needs to be rehoned with tape, or it’s bevel needs to be reset. If a razor asks for heavy bevel work, and you plan on using some extra pressure to speed up the process, it’s best to add two layers of extra tape. Hence 3 layers if you planned on honing with 1 layer of tape and 2 layers if you planned to hone without tape. This will counteract the widening of the bevel sides, that occurs when you flex the blade a bit by pushing it down on the hones. As soon as you decide to back off on the pressure, the tape can be removed, at which point you’d have some extra work to set the correct angle. This is only recommended if you need to rebuild a large part of the bevel. Normally it is better to stick with the regular low, lower and lowest pressure.
Apart form the regular X-stroke that comes highly recommended for proficient razor honing, we also can speed up the early stages of bevel formation by adopting the techniques from regular tool and knife honing. Working on one side of the blade with circling, or back and forth motions, can really speed up the process without adverse effects, as long as we make sure the razor stays flat on the hone. As soon as the bevel shows signs of completion on some parts of the blade, regular X-strokes are in order again.
Rarely the blade part is perfectly straight, even if the tool is called “straight razor”. Small deviations in the blade geometry are usually impossible to perceive as such, but they do show up in the width of the bevel sides, and can play tricks while honing.
how warp affects the bevel
If we look straight down on a bevel, we can see three lines: the left boundary, the tip of the bevel, and the right boundary. The boundary lines are defined by the razor. If they have a slight curve, due to warp in the blade, we cannot alter them with honing. The centerline, which is the tip of the bevel -the very edge-, can be influenced by our honing. As long as the warp is small enough to allow a centerline between the boundaries, there’s no real problem. The boundary lines will only not be equidistant. Or, in simpler words, there will be unevenness in the bevel, but the edge will be just as sharp. As shown at n°2 in the drawing.
In the most extreme form, the warped part of the edge only has a half bevel. The centerline occupies the same space as one of the boundaries. It is clear that this will affect the ruggedness of the edge.
If the warp is so severe that an edge between the boundaries is not possible, than the affected part will form a concave, recessed part at the edge. If present at the middle of the blade, the result is a “frowning edge”. The X-stroke can deal with this problem: by shifting the points of contact that the blade makes with the hone, the stroke follows the curvature of the blade. As a result, the centerline will start to follow the boundaries to some degree. As shown at n°3 in the drawing. This is one of the counterintuitive reasons why the X-stroke will prevent a frown, rather than causing one.
The main challenge when dealing with these kind of issues, is not to panic. Adopt a steady, even X-stroke and stay tuned. It may take some time, but in the end, you will be rewarded with a good bevel.
- Main article: Rolling X stroke.
Many older razors have a curved edge and often also a curved spine. This has its advantages, in particular for shaving hollow parts of the face and neck. Setting a hollow bevel can be tricky, for the obvious reason that it can’t be done with the regular X-stroke. The remedy is called “the Rolling X stroke”. You have to look at the blade as a section of a much larger half round disk. For sharpening such a moon-shaped object, you need to rock it. The stroke starts with the heel resting on the hone together with its opposite part of the spine, but the razor is tilted a bit, so that the toe is a bit higher. During the X-stroke, the razor is rocked over the middle part and ends with the toe touching the hone while the heel is tilted a bit upwards. If you keep an eye on the wave of water in front of, and running up, the edge, then you can adjust your stroke to reach a nice and even curve. It takes some persevering practice to get the hang of it.
The Arsenal of Strokes
In the next article, more information is provided about the available strokes for razor honing.
Strokes for honing a razor
--Bart 00:42, 6 January 2009 (UTC)