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 post 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, I need to clarify something.

Some of our Gentle Readers have been blessed with the opportunity to learn about tools from accomplished Japanese craftsmen, as was I, or have figured them out on their own. If you find this or other posts boring, please remember this blog’s primary purpose is to provide instruction to our Beloved Customers who 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.

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 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 real-world return we can quantify financially. The investment I encourage you to make is not in things, therefore, 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 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, scooping motion where a rounded bevel provides better control. Another 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.

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

Our Beloved Customers are, without exception, extremely intelligent people, so right now some of you are no doubt saying to yourself: “Self,” (that’s what they call themselves when they silently cogitate profound matters) 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 University of Tokyo 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 types are sharpened to the same bevel 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 in his research room.

But the most important point, and one I want you to grasp with both hands and feet and all your teeth is that the time expended and amount of stone consumed when sharpening by hand 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 need to 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 the same level of sharpness every time. Unfortunately, the sharpness of the bulging bevel is 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 a significant number of strokes to be wasted on polishing a mound of metal that does nothing to make the blade sharper, but is simply in the way. Not convinced? 

Consider the undeniable fact that, despite your best efforts, this irrelevant 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 micron 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 a bulging 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 colleague’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 set 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 same number of strokes. 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 you 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 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, and twist themselves into knots defending their inadequate techniques. 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 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 post 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. So sad.

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 case 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 wasting only the absolute minimum of valuable time, steel and stone.
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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.

YMHOS

Links to Other Posts in the “Sharpening” Series

Sharpening Japanese Woodworking Tools Part 1

Sharpening Part 2 – The Journey

Sharpening Part 3 – Philosophy

Sharpening Part 4 – ‘Nando and the Sword Sharpener

Sharpening Part 5 – The Sharp Edge

Sharpening Part 6 – The Mystery of Steel

Sharpening Part 7 – The Alchemy of Hard Steel 鋼

Sharpening Part 8 – Soft Iron 地金

Sharpening Part 9 – Hard Steel & Soft Iron 鍛接

Sharpening Part 10 – The Ura 浦

Sharpening Part 11 – Supernatural Bevel Angles

Sharpening Part 12 – Skewampus Blades, Curved Cutting Edges, and Monkeyshines

Sharpening Part 13 – Nitty Gritty

Sharpening Part 14 – Natural Sharpening Stones

Sharpening Part 15 – The Most Important Stone

Sharpening Part 16 – Pixie Dust

Sharpening Part 17 – Gear

Sharpening Part 18 – The Nagura Stone

Sharpening Part 19 – Maintaining Sharpening Stones

Sharpening Part 20 – Flattening and Polishing the Ura

Sharpening Part 21 – The Bulging Bevel

Sharpening Part 22 – The Double-bevel Blues

Sharpening Part 23 – Stance & Grip

Sharpening Part 24 – Sharpening Direction

Sharpening Part 25 – Short Strokes

Sharpening Part 26 – The Taming of the Skew

Sharpening Part 27 – The Entire Face

Sharpening Part 28 – The Minuscule Burr

Sharpening Part 29 – An Example

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The Essential Oilpot

If set up and maintained properly, the blades of quality chisels and planes will endure many decades of hard daily use. Maintenance is the hard part. This blog is about a tool that will not only make the chore of constant maintenance easier and more efficient, but will also make your other tools work 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 (油壺)as it is called in Japan, is a very useful, inexpensive, easily made, and time-proven tool for this purpose.

Friction Reduction

But oil pots are not just for the important job of keeping away corrosion. An oilpot close at hand will help to minimize the friction your chisels, saws, planes, and knives generate when cutting wood. The most striking benefit of this is that you won’t need to expend as much energy when working wood and your apparent strength and endurance will increase.  Perhaps more importantly, the wood being cut will be less able to deflect your tool’s blade away from the intended line of cut, increasing the precision of your work.

Besides chisels, planes and knives, the oilpot can be used to lubricate drill bits and augers.

You only need to look back in history a little way to see that these benefits are well established.

We know from the archaeological record that tallow, just rendered animal fat, was placed in grease pots and 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 aeroplanes) is oxidized and hardened tallow combined with dirt.

Indeed, I can recall my father, uncles, and grandfather using sticks of caning wax (a petroleum product) 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 the method I will describe in this post is a serious improvement over the ancient methods, in my opinion.

Making the Essential Oilpot

In Japan, an oilpot is made by cutting a joint of well-dried bamboo into a cup 3 to 4 inches deep. If you do not have bamboo where you live, a hollowed-out piece of close-grained barrel-making wood like 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 or ceramic or any other material approaching the hardness of a chisel blade.

Shape the cup so the bottom is very stable. Some people scallop the bottom so it essential 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 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

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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.

Next you will need 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 it up very tightly, and bind it 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  ¼” to ½” projecting above the lip. It must be a tight fit to prevent the wick from falling or pulling out accidently.

Add Oil

Now that the oilpot is made, we need to add some oil, so 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.

In Japan, I was told to use vegetable oil and change the wick when it became rancid.  But I recommend you save yourself some trouble and at least one stinky wick and use a non-organic oil from the start.

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

Some people prefer camellia oil, but 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 ridiculously high price tag, much like commercial furniture oil. Caveat emptor, baby. But in truth, mineral oil is not only cheaper (sold as lubricant laxative in pharmacies), but performs better than genuine camellia oil because it will not become rancid and gummy.

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

Oilpot Storage

Store your oil pot 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 to make the bottom and domed one left lose as a lid. Place some newspaper in the bottom of your container to absorb oil and stop the rattling noise.

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 the cutting edge of your chisel 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 will make you smile like a lunatic.

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 quick bit of oil from your ever-present oil pot will prevent rust and frustrate corrosive pixies.

During use, the cloth will naturally become frazzled and covered 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. If ignored, frikin Murphy will smugly use your oilpot to damage your tools and ruin your work. But never fear: If you simply brush the cloth vigorously with a steel-wire brush, sawdust, wood chips, dust and grit are easily removed.

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

When necessary, 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.

The oilpot is an ancient, dirt-cheap tool you will find to be a invaluable addition to your woodworking tool kit.

YMHOS

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