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Modifying Safety Razor Aggressiveness & Efficiency with Blade, Shims, Reverse Shims, and Tape Strips

Summary

  • A guide for modifying DE and SE safety razor aggressiveness and efficiency is presented and explained in detail
  • Modifications of blade width, blade thickness, shims, reverse shims, and tape strips under cap edges are considered with respect to their effects on safety razor parameters, particularly blade exposure and guard span
  • Aggressiveness (the ability to cut and irritate skin) and efficiency (the ability to cut hair close to skin) are distinct concepts and, in the simplest approximation, follow guard span and blade exposure, respectively
  • Blade rigidity (the resistance to blade cutting edge deflection) also relates to aggressiveness and efficiency and should be considered, along with blade sharpness and smoothness, when modifying safety razors
  • Modifications are impractical or infeasible for some DE and SE safety razors, especially those SE safety razors that only allow room for the blade to be inserted
  • The guide includes a convenient, easy-to-use table on what modifications to use in order to achieve the desired effects on blade exposure and guard span
  • It is best to physically check blade exposure using a small smooth flat piece of hard plastic

Introduction


On October 8, 2017, I posted my review of the Edwin Jagger (EJ) Kelvin with the standard DE89 head found on all other Edwin Jagger razors (B&B URL). My tailoring of aggressiveness and efficiency with the blade, shims, and tape strips was illustrated and discussed in that review, and on October 10, 2017, I asked whether I should start a separate thread about the use of tape and shims to modify aggressiveness (B&B URL). The response was positive and led to the development of this broad guide for modifying double-edge (DE) and single-edge (SE) safety razor aggressiveness and efficiency with blade properties, shims, reverse shims, and tape strips under cap edges.

Guide for Modifying DE and SE Safety Razor Aggressiveness and Efficiency


The guide for modifying DE and SE safety razors is shown below. The sections that follow offer further details. This guide for modifying aggressiveness and efficiency with blade width, blade thickness, shims, reverse shims, and tape strips under cap edges applies to safety razors in general, both DE and SE. How the modification options affect safety razor parameters is explained, especially with respect to guard span and blade exposure as they generally relate to aggressiveness and efficiency, respectively. The guidance offered here is not meant to apply for all DE and SE razors, since some modification options are not practical or feasible for certain razors, and some users may be opposed to modifying their razors. However, for those that can and wish to modify their razors in the hopes of better shaves, this guide should prove useful.



Guard Span and Blade Exposure Relate to Aggressiveness and Efficiency


It is important to define the terms "aggressiveness" and "efficiency". Aggressiveness is the ability of a safety razor with blade to cut and irritate skin, while efficiency is the ability of a safety razor with blade to cut hair close to skin. In other words, aggressiveness is the potential for cuts and irritation, especially with bad technique, while efficiency is the potential for getting close shaves, especially with good technique. Aggressiveness and efficiency are distinct concepts, even though razors are often labeled on a single scale from very "mild" to very "aggressive", and yet, aggressiveness and efficiency are related. There is an interconnectivity, but in the simplest approximation, aggressiveness goes with guard span and efficiency goes with blade exposure.

Guard span and blade exposure are illustrated in the guide above such that guard span is the distance along the shave plane from the blade cutting edge to the safety razor guard and blade exposure is the displacement of the blade cutting edge from the shave plane with the positive direction pointing away from the razor. Blade angle, cap span, and handle angle are also shown, but when it comes to aggressiveness and efficiency, guard span and blade exposure dominate. The greater the guard span, the greater the potential for skin to snag or bunch up in front of the blade cutting edge, increasing the likelihood of cuts and irritation. Greater blade exposure also increases blade feel and the risk of getting "bitten", too, but blade exposure is more related to efficiency, since more blade exposure brings the blade cutting edge closer to the skin for a closer shave.

Blade rigidity, the resistance to blade cutting edge deflection, also relates to aggressiveness and efficiency. Sharpness and smoothness of the blade matter, too. All of these factors should be considered when modifying a safety razor.

Effects of Individual Modifications on Safety Razor Parameters


The guide presented here considers five modifications: blade width, blade thickness, shims, reverse shims, and tape strips under cap edges. Their effects on safety razor parameters are succinctly tabulated in the guide, but supporting details are provided in this section.

Blade width, the distance between cutting edges for a flat DE blade or the distance between the cutting edge and the spine edge for a flat SE blade, varies from brand to brand. The most important effect of blade width is that increasing/decreasing blade width increases/decreases blade exposure, which generally increases/decreases efficiency outside of changes that are directly related to blade sharpness and smoothness. Another important effect of blade width is in how using blades with more width results in less guard span, which generally results in less safety razor aggressiveness. More blade width also results in less blade rigidity and more cap span, but these effects are usually less significant compared to the effects on blade exposure and guard span for actual safety razors. Blade width has no effect on blade and handle angles.

Blade thickness has almost no effect on blade exposure, guard span, cap span, blade angle, and handle angle, given the relatively small variations in blade thickness, but blade thickness does significantly affect blade rigidity. Blade rigidity is proportional to the material's elastic modulus and the cube of the blade thickness. With elastic modulus being fairly consistent across different steels, regardless of tempering or hardness, a 0.1 mm thick blade is calculated as having about 137 % of the rigidity of a 0.09 mm thick blade. Blade deflection is inversely proportional to blade rigidity, so a 0.1 mm thick blade will have about 73 % of the deflection of a 0.09 mm thick blade.



Shims are by far the most common modification. Shimming is known for making safety razors more aggressive. This is usually explained by how shims increase the blade gap between the guard and the blade cutting edge, but the increases in guard span and blade exposure generally account for the performance difference in aggressiveness and efficiency. The illustration above shows how the increases in guard span and blade exposure occur due to the shims moving up the blade and cap and making the shave plane more vertical. Cap span is likely to insignificantly change. Blade angle increases, which affects aggressiveness and efficiency, but in a considerably smaller way compared to the increases in guard span and blade exposure. Handle angle decreases by the same magnitude that blade angle increases. Geometric differences aside, shimming is known for increasing blade rigidity, which happens because of the extra support provided to the blade by the shims.

Reverse shims may not be as commonly used as shims, but they can be as useful for razor modification. As depicted by the illustration above, reverse shims raise the cap and shift the shave plane to a more vertical angle. In the process, reverse shims decrease blade exposure, which effectively decreases efficiency, while insignificantly altering guard span and aggressiveness. Cap span is, of course, increased by reverse shims, which could affect razor performance. The changes to blade and handle angles are practically or identically the same as with shims. The increase in blade rigidity also parallels that with shims, except that reverse shims add support along the top of the blade.

Tape strips under cap edges have been used by few and have only recently been photographed (B&B URL), but tape strips should become known as a useful modification option, just as much as shims and reverse shims. The picture above shows how tape strips deflect the blade cutting edge, causing blade exposure and guard span to decrease. Thus, tape strips effectively cause less aggressiveness and efficiency, although the effect to efficiency is likely to be most pronounced. Blade angle is also decreased by tape strips, probably resulting in further, yet minor, drops in aggressiveness and efficiency. The decrease in guard span is accompanied by an equal and opposite increase in cap span. Handle angle is unaffected by tape strips because they do not change the shave plane. Blade rigidity, on the other hand, is decreased by tape strips, since they increase the distance that the blade is free of contact from the cap and they also make the cap support softer. The decrease in blade rigidity would be expected as minor compared to increases in blade rigidity from shims and reverse shims.

Practicality and Feasibility of Individual Modifications


Important points should be made with respect to the practicality and feasibility of the various modification options:
  • Blades with different properties are available for almost all safety razors. Unfortunately, blade width and thickness are only practical options when the user knows what they are. The user cannot be expected to measure razor blades, but if the user wants a blade with a different width, thickness, sharpness, and/or smoothness, a robust table with overall dimensions and user ratings would be easy to use. Such a table has been started for DE razor blades (B&B URL). It is possible for users to become familiar with which blades are particularly wide, narrow, thick, and thin, just as users become accustomed with blade sharpness and smoothness.
  • The typical adjustable razor raises or lowers the blade and cap, which is like adding or removing shims without getting extra blade rigidity. Shims increase the blade exposure, the guard span, and the blade angle, so the typical adjustable razor does the same when increasing its level.
  • Shims, reverse shims, and tape strips are not feasible options for some safety razors, especially those SE safety razors that only allow room for the blade to be inserted.
  • Tape strip layers may be different on each side of a DE safety razor head for asymmetric performance. For example, tape strips can be added under one cap edge only for a side with less aggressiveness and efficiency.
  • Tape strips are impractical for razors in which the blade is simply cantilevered by the cap and baseplate, since the tape would just be clamped between the cap and blade and not cause any downward deflection of the blade.
  • Tapes are made with different backing materials and adhesives, so tapes vary in (a) thickness, (b) elasticity, (c) ease of cutting with scissors, (d) ease of applying to the underside of a cap, (e) durability when exposed to water during shaves, and (f) ease of removal of residual adhesive. Painter's tape is the author's preferred choice, based on experimentation with many tapes.

Modifications for Desired Changes to Blade Exposure and Guard Span


Irrespective of practicality and feasibility, individual modifications can be combined in order to combine their effects. The bottom table in the guide shows the combinations of modifications that yield increases (+), insignificant or no changes (∼), and decreases (−) in blade exposure and guard span. This table naturally follows from the table for individual effects on safety razor parameters, but the best combinations are not easily determined at first glance. Hence, it is fitting to have the combinations presented in a convenient table to make it easier for the user to modify safety razor efficiency and aggressiveness with respect to blade exposure and guard span, respectively.

The user needs only to decide what changes are desired for blade exposure and guard span in order to find what modifications are prescribed for the desired effects. Let's take the simple case of no desired changes in blade exposure (∼) and guard span (∼). We move down the table to the corresponding row and see that the table shows to add more shims (+) and more tape strips (+). This is because tape strips rotate the blade down while shims push the blade and cap up, resulting in a combined effect of the blade cutting edge roughly staying put relative to the shifted shave plane. The precise number of shims depends on the geometry of the tape with the particular razor and blade, but with some trial and error, the user can figure out a combination that works. Adding tape strips and shims to yield a similar blade exposure and guard span might seem odd, but the modifications cause an overall increase in blade rigidity.

A few more features should be understood when reading the final table of the guide. The first case in the final table, the case for more blade exposure (+) and more guard span (+), is illustrative. The table advises by a greater-than sign (>) that more shims (+) should be added than reverse shims that are added, if any (possibly +), which is because adding shims increases guard span and adding more shims than reverse shims creates a net positive change in blade exposure. Changes in blade width and tape strips could be employed, as well, but more complicated configurations go beyond the simpler guidance offered by the table.

The guidance for less blade exposure (−) and more guard span (+) is also simple, but it involves two options separated by a horizontal dotted line. The first modification option is simply to use less blade width (−). The second modification option is to add shims (+) and reverse shims (+), but less (<) shims than reverse shims, since adding more reverse shims than shims would cause a net negative change in blade exposure and the positive change in guard span would be due to the shims alone. The horizontal dotted line between the two options indicates that either option may be used alone or both options may be used at the same time to accomplish the desired effects.

Checking Blade Exposure with Small Smooth Flat Piece of Hard Plastic


Modifying safety razors can be made easier and more reliable with a simple check of blade exposure, which is usually more sensitive than guard span to configuration changes. Blade exposure can be physically inspected with a small smooth flat piece of hard plastic, such that the piece will (a) teeter on the blade cutting edge when blade exposure is positive, (b) contact both the guard and the cap but catch on the blade cutting edge when blade exposure is zero or neutral, or (c) freely slide back and forth against the guard and the cap when blade exposure is negative. The author's plastic piece is pictured below as it is lightly situated in a horizontal position against a razor head.



The smooth flat piece of clear hard acrylic is about 1 cm wide by about 3 cm long by precisely 1.91 mm thick, but the dimensions are not critical. Any small, smooth, flat piece of hard plastic will do. The piece just needs to be small and light enough to allow for the user to physically feel and check blade exposure at different points along the blade cutting edge. One finger is used to move or teeter the piece around, depending on the blade exposure. As can be observed in the picture above, the author's clear acrylic piece has acquired many fine scratches. The scratches have accumulated after much use of the acrylic piece, which is still working as well as when it was first used.

Real Examples of Modifying Safety Razor Aggressiveness and Efficiency


The method described above for checking blade exposure was employed in the real examples of safety razor modifications that are pictured below. In the default configuration, without any modification, the blade exposure was positive, as confirmed by the teetering of the small plastic piece against the blade cutting edge. A narrower blade, as pictured in the top-right corner of the picture, decreased the blade exposure, making it slightly positive or neutral, and increased the guard span.



The bottom-left corner of the picture shows the original configuration, but with two shims and two reverse shims. This situation with the same number of added shims and reverse shims is shown by the guide's bottom table as resulting in a similar blade exposure and an increased guard span, and as verified with a small plastic piece, the blade exposure was very similar as before with no modification. The shims and reverse shims also increased the blade rigidity and the blade angle, which certainly affect aggressiveness and efficiency to some extent. The bottom-right corner of the picture shows what happened to the default configuration when one layer of blue painter's tape was added under the top cap edges and one shim was added under the blade. According to the guide, this modification would either cause blade exposure and guard span to hardly change or cause both blade exposure and guard span to decrease. Given the particular razor and blade and the specific modifications, the latter case occurred such that the blade exposure decreased to being slightly positive or neutral. Guard span decreased, as expected, and so did blade angle. Blade rigidity was believed to have increased overall on account of the shim increasing blade rigidity more than the tape strip layer decreased blade rigidity.

Acknowledgement


Special thanks belong to @Cal for his helpful feedback. Cal's suggestions and questions really helped improve the guide. Thanks, buddy. :001_smile

Final Thoughts


Different reactions to this guide are expected. Whatever you might think about it, please, at least THINK about it. Even if you might be against the idea of modifying razors, you could use this guide to briefly investigate changes in blade exposure and guard span, which could lead to a better understanding of what works best for you and ultimately lead to razors that are better suited for you. Look at me. At first, I was against the idea of modifying razors out of principle, but now, I experiment with razor modifications and I'm the one who just put together a guide for others to tinker with their razors. :001_smile
 
Great thread. I've been searching for something like this for quite a while. I have found only half the information, & that in bits n pieces.
I like mild razors like the slim twist & Feather popular. I'll be trying to use a reverse shim to control my more agressive razors.
 
well, I had never heard of the reverse shim, which I'm going to try.
I'd never heard of the reverse shim, either, until I thought of adding tape strips, researched the issue, and only found one guy who wrote a little about how he used tape strips to tame his Muhle R41. It was in that research that I found "reverse shims". :001_smile Reverse shimming isn't as commonly known as shimming, but they are both valuable.
 
Great thread. I've been searching for something like this for quite a while. I have found only half the information, & that in bits n pieces.
I'm glad that you've found what you're looking for. :001_smile My analysis and write-up is original and will hopefully become a standard reference for safety razor modification.

I like mild razors like the slim twist & Feather popular. I'll be trying to use a reverse shim to control my more agressive razors.
I've never tried either of those razors, but I'd like to at least analyze the Feather Popular someday. As for taming your more aggressive razors, reverse shims will drop the blade exposure, but not the guard span. I'd recommend first trying tape strips. Tape strips drop both guard span and blade exposure. This is my favorite option. I personally use tape with or without shims. That's been working well for me, but it all depends on the razor that you're using and how you want your razor to work. For a different razor, I might find that tape strips make it too mild and inefficient.
 
I'm glad that you've found what you're looking for. :001_smile My analysis and write-up is original and will hopefully become a standard reference for safety razor modification.



I've never tried either of those razors, but I'd like to at least analyze the Feather Popular someday. As for taming your more aggressive razors, reverse shims will drop the blade exposure, but not the guard span. I'd recommend first trying tape strips. Tape strips drop both guard span and blade exposure.
You have a point. Strips will increase the curve of the blade. Its just that they seem a bit fiddly to apply. Shims are simpler. I'll try both.
The Gillette Slim twist TTO was the British version of the Knack.
Very mild razor & the handle had good grip.
 
I think it's great the effort that went into this article. You are good at describing what folks do to adjust razors to their liking. (you are like a Razor scientist in my view)
 
Great write up, buddy! I'd like to challenge a couple of points though if I may.

Blade rigidity with tape strips:

Wouldn't this increase rigidity? Firstly you are increasing the arc length from the centre point of the blade to it's last point of contact ... or are you? I'm not entirely convinced by my own perspective here to be honest, but it might be worth giving it a second look at yourself. Secondly, due to Hooke's Law, the increased curvature of the blade will increases the forces exerted by both blade and cap. Although there is no lower clamp at that point, the upward force against the last support point is most certainly greater. This should increase rigidity (and reduce chatter).

Efficiency Definition:
I'll try to use your terminology as much as possible so that we are on the same page. I think if the blade crosses the neutral plane or shave plane in any direction (as you pointed out to me in my walkthrough, some start off recessed), then I would agree that the modification has increased or decreased the efficiency of the blade. However, if the blade is proud before and after the modification, the efficiency of the razor is unchanged. The blade is still just as able to shave at skin level as it was before. What has changed though, is the angle range between cap riding and guard riding. I'm not convinced that's a reduction in efficiency though. In use, I would personally find that efficiency unchanged, as I would just compensate the presentation angle ...

Aggression vs Efficiency:
"There is an interconnectivity, but in the simplest approximation, aggressiveness goes with guard span and efficiency goes with blade exposure" (first paragraph after the tables)
You might want to rephrase this bit. The guard span does allow more room for skin to bunch up if not held taut or pressure is applied, I'm somewhat neutral there, but I shall yield to your judgement - but I think the biggest contributor to aggressiveness is still the blade exposure. I also think the efficiency is whether the blade is proud, level, or below the "shave plane", not how far proud it is. Going from one point proud of that plane, to a second point even further proud of that plane, certainly increases aggression - but does it really make it any more efficient when it was capable of shaving at skin level already?

I'm not a modifier, as I think modifying the technique trumps any changes to make to the kit, but this is certainly a useful guide for those who are still looking towards hardware changes for them to achieve different results. It also lets people do a dry run on a different type of razor, before purchasing something which might not be to their liking.

You might also want to suggest using a sacrificial blade for measuring the blade exposure, so that folks aren't shaving with a blade that's been digging into a piece of acrylic, and possibly affecting the edge ...
 
I think it's great the effort that went into this article. You are good at describing what folks do to adjust razors to their liking. (you are like a Razor scientist in my view)
I appreciate that. Thanks. Yes, this work was a long time in the making. A lot of hours and photos and PowerPoint stuff. "Razor scientist"? I like that! Thanks! :laugh: :blush:
 
You have a point. Strips will increase the curve of the blade. Its just that they seem a bit fiddly to apply. Shims are simpler. I'll try both.
The Gillette Slim twist TTO was the British version of the Knack.
Very mild razor & the handle had good grip.
You're right that tape strips are "a bit fiddly to apply" while shiims are much easier to add and remove. I'm going to add something about that. It takes a little time to cut and apply them, and it can be a little frustrating, but with experience, the process gets easier. The tape really matters, too. Painter's tape is my favorite and makes the whole process of applying and removal fairly easy compared to other tapes. Once you get the strips on, and you like them where they are, they will last for a very long time. I don't even know how long they truly last because I end up modifying my razor again for one reason or another.
 
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