Sharpening Part 21 – The Bulging Bevel

This is what a flat bevel looks like. So sweet.

For everybody in their busy lives, you need to invest in sharpening your tools, and you need to invest in longevity.

Ryan Holmes

In the previous article in this series about sharpening tools we looked at why and how to true the ura, the hollow-ground area on Japanese chisel and plane blades. This post will focus on the opposite side of the wedge that is a cutting edge: the bevel. This discussion is relevant to all plane and chisel blades, not just Japanese tools.

Preface

Before we dive in, Your humble servant must clarify something.

Beloved Customers and Gentle Readers that have been blessed with the opportunity to learn about tools from accomplished Japanese craftsmen, as was I, or that have figured them out on their own, and consequently find this or other posts boring, should remember that the primary purpose of these writings is to provide instruction to our Beloved Customers, some of whom have not had similar opportunities.

These Beloved Customers are located in many countries and range in experience from newbies to professional woodworkers, so I try to include both advanced information for the professionals, and detailed explanations so newbies can keep up. Consequently, these articles are sometimes long and wordy. I humbly request your kind indulgence on behalf of those who may benefit from extra words.

Investing in Longevity

The quote above by Mr. Holmes is applicable to the all the principles of sharpening I have described in this series of posts so far. He is a computer dude, not a building contractor, joiner or furniture maker, but it is no coincidence he chose to use handtool terminology: it is encoded in human DNA.

His first point is a self-evident admonition, but what about this “investing in longevity” stuff? By definition, an investment is an expenditure of time, resources and/or effort intended to produce a return greater in value than the expenditure. Then how do we go about investing in the longevity of our chisels and planes, and what return should we expect?

While simply grinding sharp edges on our tools helps with making things from wood, I don’t see it as an investment in tools. Rather, if we train ourselves in professional sharpening techniques, and use those techniques to maintain our tools so they function more efficiently and last longer, we can hope to obtain a quantifiable real-world ROI.

The investment your humble servant encourages you to make, therefore, is not in stuff or lucre but in your own skills.

The Pros and Cons of the Bulging Bevel

The “bulging bevel,” as I call it, is a deformation too frequently seen in plane, chisel and knife blades. It is simply a cutting edge bevel that is protruding and convex instead of flat. In most cases a bulging bevel can make it difficult to properly sharpen a blade adequately, so it deserves our attention.

Most bulging bevels are born unintentionally and are harmful, but indeed some are hatched with a purpose in mind. Let’s examine the pros and cons, and throw in some scientific results just for fun. 

The geometry of the bulging bevel is clearly superior in a few applications such as carving chisels and knives used in a gouging or scooping motion where a rounded bevel provides better control. Another valid application is chisels used for cutting large and deep mortises where a rounded bevel helps pop out waste easier. Only timber framers cut these kind of mortises, however, and most of them use machines to at least rough out the mortises nowadays.

Hidari no Ichihiro 42mm Oiirenomi. Nothing obese about this sweetheart’s bevel.

Our Beloved Customers are, without exception, extremely intelligent people, so right now some are no doubt saying to themselves: “Self,” (that’s what BCs call themselves when they silently cogitate matters of great weight) does a rotund bevel make my blades sharper or duller?” Let us consider some scientific results.

When I was a grad student in Japan, a fellow student wrote his thesis on the efficacy in plane blades of the bulging bevel versus the flat bevel. He developed experiments, fabricated testing apparatus, and used scientific methodology and microscopic photography yielding indisputable results. We repeated some of his experiments, discussed his research, and pored over photographs and fondled shavings late into the evenings at his lab in Building 11 at the University of Tokyo’s Hongo campus as I drank coke and he drank sake. I’m not sure he made it home some evenings.

The conclusion he reached was that, from the viewpoint of the wood, and based on the classic sharpness test of cutting rag typing paper, there is no difference in the cutting performance between flat and bulging bevels, so long as two conditions are met: (1) Both flat bevel and bulging bevel are sharpened to the same angle and same degree of sharpness; and (2) The bulge is not so large as to interfere with the cut. The “same degree of sharpness” condition in proviso 1 is critical to this discussion.

Let’s examine the cutting edge closely. It’s effective scope is only the last few microns (μ) or so of the blade’s width at the extreme edge. 1μ = one millionth of a meter. A human hair is 90μ in diameter. We need to precisely repair and polish this narrow strip of steel using our sharpening stones, but remember that working anything beyond this strip contributes nothing to making the blade sharp.

Here’s an important point we can learn from a careful examination: Given the same number of strokes to the same blade on the same stones over the same amount of time, it is difficult to make a bulging bevel as sharp as a flat bevel, unless one spends the time to use a sharpening machine and jigs as my grad school friend did during his research.

But the most important point, and one I want you to grasp violently with both hands, at least two feet, and all your teeth is that the time expended and amount of stone consumed when sharpening to a set level of sharpness at the last critical microns of a bulging bevel’s cutting edge is huge compared to a flat bevel. Sharpening using machines and/or honing jigs takes even longer.

In addition to time and cost, another factor we must consider is certainty, because if we are going to invest the time and stones to sharpen a tool, we need to be sure it will consistently achieve approximately the same level of sharpness every time. Unfortunately, the sharpness of the bulging bevel is often uncertain because, instead of guiding the blade to ensure consistent contact between steel and stone at the critical location on the cutting edge, the shape of the bulging bevel causes us to waste a significant number of strokes and time on polishing an irrelevant mound of metal that does nothing to make the blade sharper, but is simply in the way. Not convinced yet? 

Consider the undeniable fact that, despite your best efforts, this miserable lump causes the blade to rock around on the stone’s surface like a boat over ocean swells, with the result that, given a fixed number of strokes, a high percentage of those strokes end up polishing the bulge instead of the cutting edge. This is important because, once again, the last few microns of the blade is the only part that actually does any cutting, not the bulge. 

Please don’t misunderstand. I’m not saying that you can’t create a fiendishly sharp edge on a blade with an obese bevel. I’m also not saying that, within reasonable parameters, a convex bevel cuts less efficiently or dulls quicker than the same blade with a flat bevel. It absolutely doesn’t, as my fellow student’s research showed. Allow me to restate and summarize the facts so there is no confusion.

  1. It takes longer to create a given level of sharpness at the extreme cutting edge of a bulging bevel than a flat bevel, all else equal;
  2. It consumes more sharpening stone to achieve a given level of sharpness at the extreme cutting edge of a bulging bevel compared to a flat bevel, all else equal; and  
  3. There is greater uncertainty about the actual degree of sharpness achieved at the blade’s extreme cutting edge when sharpening a bulging bevel by hand compared to a flat bevel, all else equal. 

If you doubt these statements, you must find the truth yourself.

Buy or borrow a quality loupe or microscope with enough magnification to detect the scratches left by your usual finishing stone. Start with a dull blade with a truly flat bevel, sharpen it freehand using a pre-determined number of strokes, and observe the scratches at the last few microns of the cutting edge with your microscope. Then test the blade’s sharpness with your skin or fingernail. Next, repeat this test with a dull blade with a rounded bevel using the exact same sharpening tools and procedures and the exact same number of strokes. No deviations. Once again, observe the scratches and test the sharpness. My grad school friend and I performed this side-by-side experiment at the University of Tokyo several times, with consistent results. Actually, it was a bet and I won. He had to buy the drinks and snacks for a month.

The Causes of Bevel Obesity

Besides pernicious pixies, the most common cause of bevel bulge is simple carelessness, which Beloved Customer can take steps to avoid once you realize the causes.

It is human tendency to try to stabilize the blade’s bevel on the stone while sharpening by applying more pressure on the rear half of the bevel, resulting in the rear half of the bevel (which is all soft jigane in the case of Japanese plane blades, and mostly soft jigane in the case of chisels) being abraded quicker than the front half (which contains the harder steel lamination), causing the bevel angle to gradually decrease or even become rounded. Even the best craftsmen make this mistake sometimes.

To avoid this tendency, train yourself to focus pressure on the front half of the bevel closest to the cutting edge. At first, you may overbalance and dig the cutting edge into the stone a few times, but with practice and attention, it will become second nature. It is almost a meditative process. Every professional woodworker worth his salt must learn this skill.

There is nothing wrong with making mistakes when learning a muscle memory skill like freehand sharpening, but too many people can’t be bothered to learn, and then become frustrated when their skills don’t improve immediately. In the end, they become defensive, twist themselves into knots defending their inadequate techniques, and eventually adopt the self-justifying position that sharpness is overrated. Patience, grasshopper.

BTW, don’t forget to use your handy dandy brass bevel gauge to both check the bevel angle while sharpening and to keep those piratical pixies away.

Hidari no Ichihiro 30mm Atsunomi. What ignorant, smelly savage would grind multiple bevels on this?

Another cause of the tumescent bevel is the use of secondary bevels or micro-bevels. We’ll look at these aberrations in the next article in this series.

To make multiple bevels work one almost must use a sharpening or honing jig of some sort. Many allow sharpening jigs to become a substitute for real sharpening skills they didn’t bother to learn. Such jigs can become, in effect, training wheels those who rely on them never grow out of. How amateurish.

Conclusion

I encourage you to “invest in longevity” with regards to your tools in three ways:

  1. First setup your planes and chisels properly so they will provide you with long, reliable and efficient service. Setting up chisels improves not only their longevity but in many cases their performance too, strange though it may seem. I will post articles about setting up and maintaining Japanese planes in the future.
  2. Second, true the ura of your plane and chisel blades efficiently without reducing their useful lifespan needlessly, as described in previous posts; and
  3. Third, invest in yourself by developing and honing the hand skills necessary to sharpen your blades quickly and efficiently while consuming only the absolute minimum of valuable time, steel and stone.
Image result for image of mandalorian helmet

Please master the ancient and bedrock-basic skill of freehand sharpening. All it takes is an understanding of correct principles, followed by concentration and practice; The rest will follow. I promise. “This is the way.”

We will look at other causes of bevel obesity in the next post in this series on science over barbarism.

YMHOS

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The Essential Oilpot

Little strokes fell great oaks.

Ben Franklin

If set up and maintained properly, the blades of quality chisels and planes will endure many decades of hard daily use. Maintenance is the key. In this article your humble servant will describe a tool that will not only make maintenance easier and more efficient, but will also make Beloved Customer’s tools perform better.

Tool Protection

It is a sad truth that the blades of woodworking tools often receive more damage while they are waiting to be used than when they are actually being used. Thankfully, corrosion of the sort that creates microscopic pits at the cutting edge can be easily avoided with common-sense solutions.

When not in use, store your chisels and planes where they will be protected from dust and large temperature swings. And oil your blades after every use to keep away oxygen, moisture, and chemicals that might make your expensive blades “turn red and go away.”

I suggest you plan ahead to make it as easy as possible to apply good oil to your blades. An oilpot, or aburatsubo (ah/boo/rah/tsu/boh 油壺) as it is called in Japan, is a very useful, inexpensive, easily made, and time-proven tool for this purpose.

Friction Reduction

Oil pots are not just for the important job of keeping corrosion at bay. They help minimize the friction your chisels, saws, planes, and knives generate when cutting wood, as well as the energy you need to expend in cutting. More importantly, the wood being cut will be less able to deflect your tool’s blade away from intended intended line of cut, noticeably increasing the precision of your work. You only need to look back in history a little way to see that these benefits are well established. Don’t believe me? Give it a try.

We know from the archaeological record that tallow, simply rendered animal fat contained in open grease pots was used as a tool lubricant in Europe from medieval times right up until petroleum products became widely available. It was also used in the Americas until the same time.

Vegetable oil was used in Asia, and probably in Europe as well. I am told that the black crust found on many antique plane bodies (wood planes not airplanes) is oxidized and hardened tallow combined with dirt.

Indeed, I can recall my father, uncles, and grandfather using sticks of paraffin caning wax for the exact same purpose when I was a child, and before that my English ancestors probably used beeswax and tallow candle stubs. I haven’t tried soft tallow as a lubricant and probably never will since rancid fat has even less appeal to me than rancid vegetable oil, but I’m confident you will find the solution described below a serious improvement over these ancient methods.

Making the Essential Oilpot

In Japan, an oilpot is traditionally made by cutting a joint of well-dried, large-diameter bamboo into a cup 3 to 4 inches deep. If you don’t have access to bamboo where you live, a hollowed-out piece of some close-grained wood suitable for making water-tight barrels, such as white oak, or a plastic mug, or even a segment of capped PVC pipe will work just as well. The important thing is the container not be made of metal, glass, ceramic or any other material approaching the hardness of a chisel blade.

Shape the bottom or foot of the cup so it will rest on a more-or-less flat surface with perhaps some irregularities. Some people scallop the bottom so it rests on four or five spots at the perimeter. And a piece of sandpaper glued to the bottom will prevent your planes from dragging the oilpot around when you pass their soles over the wick.

If you use bamboo or wood, prime and paint the inside of the cup, and underside of the foot, with a high-solids urethane or polyurethane paint. I used a natural urethane extracted from the cashew tree called “Cashew” on the bamboo joint in these photos. The gaudy orange color makes it easy to differentiate my oilpot from others on a jobsite

Line the inside of the cup with an unbroken sheet of aluminum foil to prevent the oil from soaking through. The paint alone will slow down the oil’s movement through the wood’s fibers, but sure as hogs are made of bacon, without a reliable liner of some sort, it will eventually seep out making a mess. Aluminum foil will fix this.

Next you will need some clean, white, cotton T-shirt fabric. Used clothing is fine. White because you want to be able to tell how dirty the fabric is at any time. T-shirt fabric because it sheds the least fibers. Clean because pixies hate it. If you don’t believe me, just ask them.

Roll the cloth up very tightly into a wick just a hair smaller in diameter than the inside of your container and bind it tightly with string or thread. It will take several tries to judge just the right amount of fabric. You should be able to force this dense cloth wick tightly into the cup with approximately ½” projecting above the lip. It must be a tight enough fit to prevent the wick from falling or pulling out accidentally, but not so tight it breaks the container.

Add Oil

Now that the oilpot is made and wick installed we need to add some oil. Just soak the cloth with your favorite lubricant and you’ll be ready to rock-n’-roll like Zeppelin. It will take some time for the oil to saturate the dense wick, so be patient or it may overflow without saturating the wick. I get impatient and spill a little oil sometimes.

In Japan, I was taught to use vegetable oil and change the wick when it became rancid, which it always did. But I recommend Beloved Customer be smarter than I was back in the mists of time and use a non-organic oil from the start. Stinky wicks are such a waste.

Some people prefer to use straight mineral oil or scented furniture oil, which is just scented mineral oil. The lemony smell is nice. But please avoid any furniture polishes or oils that contain insidious silicon because it will weaken glue bonds.

Some people prefer camellia oil, and while this has a long history of usage as a lubricant and hair oil in Japan, be aware that the so-called camellia oil available commercially for rust protection is actually just mineral oil with a bit of yellow dye and some fragrance added, sold at an inflated price, much like commercial furniture oil. Caveat emptor, baby. Mineral oil sold as lubricant laxative in pharmacies is not only cheaper but performs better than genuine camellia oil because it will not become rancid and gummy.

While it sounds strange, the best lubricant by far in my experience is a lightweight, light-colored synthetic motor oil such as Mobile-1 (5W). I have tried regular motor oil too, but the synthetic variety smells better, lasts longer and seems to perform better.

Oilpot Storage

Store your oilpot in a metal or plastic container with a lid when not in use to prevent abrasive dirt from contaminating it. Some people make a container from a segment of PVC pipe with a flat end cap glued on one end of their PVC segment to form the bottom of their oil pot and a domed cap on the other end left lose as a lid. I use a tin can with a slip-on lid.

Place some newspaper in the bottom of your container to absorb oil and cushion the pot from rattling around.

Even a plastic bag will do until you find something better.

Using and Maintaining the Essential Oilpot

When you are cutting a mortise with your chisel, make it a habit to occasionally jab its cutting edge into the oil pot, and even wipe the sides and ura (flat) on the wick to lubricate the blade. You will be pleasantly surprised to find that this bit of oil will make your chisel work not only go faster, but more precisely and with cleaner results. The oil will not weaken glue bonds.

Likewise, when using either a metal-bodied or wooden bodied plane, occasionally swipe its sole over the oil pot. This will greatly reduce friction and give you more control. But if you value your public dignity, be forewarned that the first few cuts after doing this the first time will make you grin like a lunatic! (ツ)

The same benefits of reduced friction and increased precision can be found in the case of handsaws too, although the difference may not be as noticeable.

Before you store your tools away for the day, a dab of oil from your ever-present oil pot will prevent rust and frustrate corrosive pixies.

During use, the cloth will naturally become frazzled, coated with sawdust and wood chips, and will discolor accordingly. No problemo.

If you drop the oilpot and it hits the ground, heaven forbid, Murphy’s Law of Buttered Toast dictates it will land oily-cloth down contaminating it with abrasive grit (unless you work in a cleanroom). If ignored, frikin Murphy will smugly use your oilpot to damage your tools and ruin your work. But never fear: simply brush the cloth vigorously with a steel-wire brush and all the sawdust, wood chips, dust and grit will be gone. The sound you will hear while doing this will be Murphy gnashing his teeth in frustration.

Of course you always have a steel-wire brush close at hand to remove embedded grit from boards before planing them, right?

When the wick becomes too dirty for the steel wire brush to clean (difficult to imagine though that may be) you can re-roll or replace the cloth wick to expose a clean surface.

As the cloth wears and stops projecting from the oilpot’s mouth, remove the wick and place some clean rags in the bottom to elevate it thereby restoring the necessary projection of the wick.

The oilpot is an ancient, dirt-cheap tool you will find to be a invaluable addition to your woodworking tool kit. I promise it will make you grin when using handplanes!

YMHOS

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Please share your insights and comments with everyone in the form located further below labeled “Leave a Reply.” We aren’t evil Google, fascist facebook, or thuggish Twitter and so won’t sell, share, or profitably “misplace” your information. If I lie may ticks, fleas and biting flies be my only friends.

Tool Maintenance: Corrosion Prevention