Sharpening Part 20 – Flattening and Polishing the Ura

Shall I compare thee to a summer’s day?
Thou art more lovely and more temperate:
Rough winds do shake the darling buds of May,
And summer’s lease hath all too short a date;
Sometime too hot the eye of heaven shines,
And often is his gold complexion dimm’d;
And every fair from fair sometime declines,
By chance or nature’s changing course untrimm’d;
But thy eternal summer shall not fade,
Nor lose possession of that fair thou ow’st;
Nor shall death brag thou wander’st in his shade,
When in eternal lines to time thou grow’st:
   So long as men can breathe or eyes can see,
   So long lives this, and this gives life to thee.

William Shakespeare, Sonnet 18

Your most humble and obedient servant began this post with the elegant sonnet quoted above, indisputably one of the most beautiful pieces of poetry ever written in the English language, instead of the usual pithy proverbs of Red Green, that towering Canadian Philosopher-Handyman and erudite Leader of Possum Lodge, just to show Gentle Readers how refined we at C&S Tools can be when no one is watching (ツ). But sadly we must now pause all such elegant distractions for a time to focus on the nuts-and-bolts of how to true the ura of a Japanese woodworking blade, the first step in making it sharp.

This tutorial is rather wordy because Beloved Customers sometimes find the task of managing the ura difficult at first. Indeed, while truing the ura of Japanese chisels and planes is a simple task, it’s one many get wrong the first time, occasionally resulting in emotional damage to both blade and it’s owner. I know it almost drove me non compos mentis the first few times I tried, but now that my psychiatric team has stumbled onto the right mix of meds, and Doctor Alonzo has released your humble servant from that unflattering canvas straight jacket, Beloved Customers have the opportunity to learn from my mistakes. Rejoice!

This is the first article in the series where we actually turn steel to mud, so let’s get to it.

Important General Principles

All standard chisel blades and plane blades, whether Japanese or Western, need to have a planar “flat,” or in the case of Japanese chisels “ura,” opposite the bevel in contact with the sharpening stones the blade’s full width, and ideally, full length. Perfection is not necessary, however, so don’t let yourself become obsessive; That way lies madness.

A few lost souls mistakenly assume (just before they go barking mad) that the lands surrounding the hollow-ground uratsuki must be perfectly planar for the chisel to function, but such is not the case. Granted, it does make it easier to sharpen the blade, but it need not be achieved immediately, especially since a planar ura can be easily obtained gradually over multiple sharpening sessions.

If Beloved Customer’s chisel does not have a fully-planar set of lands surrounding the hollow-ground uratsuki when new, understand that it may be a hand-forged, hand-shaped, hand-sharpened tool with imperfections, and perhaps not a CAD-CAM designed, mass-produced, chisel-shaped, sharpened screwdriver. If so, please understand that this is not an aberration but is normal. However, if such natural irregularities distract to the point your eye starts twitching like that of Chief Inspector Dreyfus after spending time with Inspector Clouseau, perhaps hand-forged tools are not your cup of tea.

Procuring Perfect Tools

The previous sentence may seem to suggest that we at C&S Tools prefer to not provide our humble tools to perfectionists, but that is not the case. Rather, we insist Beloved Customers seeking the perfect chisel plane, saw or knife fully acknowledge and comply with the rrealities procuring such tools entails nowadays. What conditions? First, multiply your tool budget at least tenfold (seriously) and set aside that budgeted amount in hard cashy money, maybe in roll in your sock drawer. You see, unlike your unworthy servant who many assume works for free, craftsmen with the skills required to produce perfect tools, and who are willing to invest their valuable time in doing so, are in high demand and do not work for free. If this seems steep, then perfection is not for you.

Next, plan your order carefully, and perhaps commission drawings. Not as easy as it sounds, mayhap.

Finally, steel yourself to wait a minimum of two years for the work to be completed, for you see, while many desire perfect tools and are willing to pay the price, you don’t need toes to count the number of overworked craftsmen that can actually forge them nowadays.

Oh yes, I almost forgot one thing. In the case of our Perfect Tool Blackmith, he has an unusual condition, one based on valid reasons I cannot disclose, that the recipient be a working professional craftsman, not an amateur, hobbyist or collector.

An option to having a perfect chisel custom-forged new is to seek out a genuine Hidari-no-Ichihiro chisel because the Yamazaki brother’s products, though very expensive back in the day and more expensive now, were pretty close to perfect in shape and appearance. But beware counterfeits.

On the other hand, the tools we sell to our regular Beloved Customers are extremely practical, they look OK, perform just as well as Perfect Tools, cost a helluvalot less, and most importantly they are waiting on our shelves right now quivering in anticipation of an airplane ride to new masters who will feed them oodles of yummy wood. So which do you think is is better? A perfect prima donna of a tool that takes years to procure and is too precious to use hard, or a reasonably-priced, hard-working, hand-forged, high-performance, eager but perhaps less than perfect tool you can have right away?

Working With the Imperfect Ura

In any case, please be aware that a chisel with an imperfect ura (nearly all of them have some problems when new) can be perfected over time and will work just fine as-is if you are patient, remain aware of the blades tendencies, and compensate using your eyes and hands accordingly. After all, the chisel only does what you direct it do, so please direct the blade instead of just going along for the ride while drinking adult beverages and smokin wacky-tabaccy in the back seat with Murphy. 〜(シ) 〜

If the plane formed by the ura’s lands is concave, the chisel will tend to undercut the end walls of a mortise, not difficult to avoid with some caution of the sort one must always exercise.

On the other hand (the one with 6 fingers) if the plane is convex, the chisel will tend to scoop away from the end walls of a mortise. All things considered, however, concave is far better than convex.

But whether concave or convex, such irregularities always exist to some degree from time to time in all chisels sharpened by hand. It is the craftsman’s job to manage his tools and find efficient ways to maintain them. Of course, this means we must strive to create and maintain a reasonably flat ura, so let’s consider some practical time-proven solutions that avoid wasting a lot of time, stone and steel, and at the same time don’t wear out the hollow at the ura in the process.

Let us begin by observing that the surface area (square millimeters) of the hard steel encompassed within the lands at the ura that we need to eventually make planar can be divided into four areas:

1. The land immediately adjacent and parallel to the cutting edge (aka “itoura;)
2. The land where the neck meets the blade, also kind sorta parallel to the cutting edge;
3. The skinny side land more-or-less parallel with the blade’s long axis and located on the right side of the hollow-ground area called the uratsuki; and it’s mirror image
4. The skinny side land on the left side of the uratsuki.

All four lands are necessary, but the one that matters most when sharpening and cutting is the last couple of millimeters at the itoura touching the cutting edge.

While some people fixate on it, the land near the neck matters least of the four. This is an important point to grasp.

The side lands are important bearing surfaces for aligning the chisel in the cut, but they are less important than the cutting edge land, the itoura. If you like your chisels and planes, prefer they remain as easy as possible to sharpen, and intend to use them for a long time, it’s important to understand that working the ura over-agressively on rough stones is the quickest way to wear the side lands down prematurely, thereby making the uratsuki shallower quicker, and defeating the subtle genius of the design of Japanese woodworking blades before their time. We want to maintain the ura as deep as reasonably possible for as long as reasonably possible.

Allow me to explain this further. As we inevitably grind away the skinny side lands, the hollow-grind at the uratsuki will become shallower and the amount of hard steel we will need to sharpen/polish will drastically increase, which is inconvenient in so many ways. Sadly, too many people make their chisel’s side lands fat as a sumo wrestler soon after purchasing a chisel in their anal-retentive quest for the totally flat ura. Makes me wanna cry.

The cost-efficient and time-efficient solution is to focus on the important itoura, make small corrections to the ura’s three other lands over multiple sharpening sessions thereby saving valuable time as well as expensive stones and steel while preserving the ura as long as possible. How to do this? Focus all your attention on the most important area, and patiently plan on accomplishing the job over 5~10 sharpening sessions, using the chisel in the meantime.

Don’t spend any effort correcting/polishing the ura full-length from cutting edge to neck, instead work the area behind the cutting edge on the stones (which must be flat). To do this, focus finger pressure nearest the cutting edge only. An effective approach is press down on the land nearest the cutting edge while moving the blade on the stones, while the rest of the blade hangs off the stone.

In other words, while pressing down with the fingertip(s) on the face of the blade (the surface opposite the ura with the brand on it) as near as possible to the cutting edge, move the last 5~15mm of the blade onto and off of the stone in a back-and-forth diagonal motion concentrating abrasion where it is needed most. This requires the ability to sense the balance of the blade on the stone, and to apply fingertip pressure where it is needed most. Wow, imagine that.. real hand skills. If you don’t have these skills now, they are easy to develop with concentration and practice.

During each subsequent sharpening session, increase the width of the area you work on the stones a tiny bit until the entire ura is flat and can be worked on the stones.

Through this technique and over multiple sharpening sessions, you will notice the ura’s lands will gradually become planar while only the lands nearest the cutting edge increase in width. Honest.

It helps to apply either marking pen ink or machinist’s blue to the blade to confirm whether or not you are applying pressure where it is need most and that abrasion is proceeding as desired.

Please also keep in mind that, when working the ura, in most cases, you should focus hand/finger pressure on the “ito-ura,” the land at the ura located right at the cutting edge, and almost no pressure elsewhere on the ura.

It is human nature to want to rely on the flatness of the ura’s lands to keep the blade flat on the stone, and therefore we tend to apply pressure at the midpoint of the back so that the pressure on the ura’s land is even at all points of contact. This feels good; It feels stable.

But if you consider the narrow width (and small area) of the hard steel exposed at the side lands compared to the lands at the ito-ura cutting edge and the corners of the blade, you will see why this technique will wear the skinny side lands quickly and prematurely.

Allow me to restate an important point: The goal therefore is to focus hand/finger pressure nearest the cutting with much less pressure focused on the sides lands preserving them, and the depth of the ura, as long as possible. This technique will also save time and expensive steel. It is an advanced skill, but one Beloved Customer should aim to perfect.

A detailed example follows.

Once the ura of your chisel is flat and true, you should not need to true it again unless the blade needs major repairs. Japanese plane blades, on the other hand, are a little more complicated because repeated sharpenings tend to gradually wear out the land right in front of the cutting edge, called the “ito ura,” and the bevel must be tapped-out to compensate, and the ura re-flattened. I won’t delve into the subject of “tapping out” the ura of plane blades in this post but a detailed explanation can be found in Part 30 of this series.

Evaluate the Ura

The first step in flattening or truing an ura is to evaluate its condition. Don’t start grinding away willy nilly without first checking it and making a plan. If you find you cannot stop yourself, don’t walk but run to the nearest pharmacy and buy a bucket of the medicine discussed in part 19 in this series about maintaining sharpening stones.

There are several ways to check the ura’s condition. A thin straightedge works well in most cases. A thick straightedge may be easier to keep stable on the ura, but it will shut out too much light making observation difficult. Place the straightedge edge-down on top of the full length of the side land all the way to the cutting edge. Keep the straightedge touching the land; Don’t let it span the hollow-ground uratsuki. Hold the straightedge and blade up to a strong light source and look for light passing between them. This technique is quick and dirty and will suffice in most cases, but does not tell you a lot about twist.

Another method to check the ura for planar is to paint the shiny lands with dark marking pen ink or Dykem liquid, apply a tiny bit of fine sharpening stone mud to a piece of flat glass, like the piece mentioned in Part 17, and rub the blade’s flat or ura over the glass. The high spots will become obvious. If the ura is banana shaped (convex), mark the high spot with your marking pen. More often than not, the ura of chisels will be generally flat, but sometimes the last 2mm or so of the cutting edge will be curved upwards towards the chisel’s face.

I learned two things from my examination of this atsunomi. First, there is a high spot (convex) at the skinny land on one side located approximately 1/2 to 5/8 the blades’ distance from the cutting edge. The land on the other side seems a little low. Hmm, curious. This is a bit unusual, but it happens when a blade warps during heat treat, which Shirogami steels tends to do frequently.

The second problem I observed was that the last 3~4mm of the itoura land at the cutting edge curves downward away from the ura just a tiny bit, enough to cause problems.

I next must formulate a plan to resolve these problems with a minimum of time and effort and without making things worse.

Make a Plan

The temptation to start grinding away immediately will be powerful. But… I must… resist… the… stupidity impulse!!

If it becomes too much, I’ll take a coffee cup or three of the medicine mentioned in the previous post and slather it on my head forcefully. Don’t hold back, for Pete’s sake, rub it in really good now. Some say my excessive use of this medicine is why I am as bald as an egg, but I prefer to believe it is caused by the high-intensity psychic waves radiating from my gigantic brain (ツ). Thank goodness for my aluminum foil skull cap with its artfully protruding copper wires or the radiating light might blind airline pilots passing overhead!

But getting back to practical matters, a useful plan must have goals and objectives. In this case the goal is a perfectly planar ura, but if this goal is difficult to achieve quickly there is an objective you achieve immediately in any case, one that may make it possible to achieve the larger goal over multiple routine sharpening sessions without any special effort.

As I keep harping, to make a chisel or plane work well, you need a sharp, flat bevel and a sharp flat area right at the thin land adjacent the cutting edge. This is where the cutting occurs and the area I need to keep sharp, so I will make creating this flat area the first objective in my plan, and then determine the steps to achieve it. I make certain every step in my plan and every stroke I make on the stones gets me closer to this objective, not further away. This means working smart, ruthlessly calming my inner badger (you know, that nearsighted, short-legged snuffling beast that just keeps digging) and repeatedly stomping my stupidity impulse into the ground. Frequent applications of idiot ointment help too.

If the blade is arched (concave), touching at two points, one near the neck of the chisel blade, or head of the plane blade, and at the other at the cutting edge, and not in between, all is well. I recommend you leave a blade like this as-is because after a few sharpening sessions the ura will become flat and twist-free without any special effort, and the blade will become very sharp and be entirely functional (assuming the faces of your stones are flat).

If the blade is wavy (rare) or banana-shaped (convex), your plan needs to take those details into account.

In this example I located the highest point of the bulging area at the ura and marked a line across it with my marking pen. I then measured halfway between this line and the cutting edge and made another line. which I will call the “focus line.” It is here where I need to focus the most pressure when grinding down the ura, NOT the entire length of the blade, despite what my inner badger demands.

The purpose of doing all this prissy planning and layout work is to protect the right and left side lands from being wasted unnecessarily. Newbies and those with poor badger control often insist on working the entire length of the blade on the stones, but this is illogical and ignores three points.

The first point often overlooked or ignored is that the majority of the metal I need to waste is usually located to the right and left of the itoura land nearest the cutting edge, not the full length of the blade, so there is little benefit to grinding the entire ura.

The second point is that the side lands are thin as a blade of grass and will abrade very quickly with almost no effort. Besides, without using large plates and stones, it is very difficult to work the blade’s full length accurately without wearing steps into the side lands anyway.

The third point often ignored is that it makes no sense at all to try to grind down the land nearest the neck since the plane of the ura hinges on this land anyway. Best to leave it alone and focus my efforts where they will make a useful improvement.

Plane blades don’t even have a land near the head, so the futility of working the entire ura on plane blades is even more obvious than for a chisel.

Work the Plan

The traditional Japanese tool used to flatten and/or correct ura is a smooth steel lapping plate called a kanaban, meaning “metal plate.” To use it, carborundum powder and water are placed on the plate, and the blade is lapped. This is not a difficult process at all, but there is a tendency for the blade’s perimeter to be ground more than the interior areas as the grit is forced in between the kanaban and the blade’s perimeter. To avoid this tendency, and to speed the process up, I prefer to use diamond plates or diamond stones instead of kanaban.

Whatever plan you developed, and whichever tool you selected for this job, the time has come to work the plan. Do you need more idiot-b-gone medicine? A bigger coffee cup?

First, color the ura’s perimeter lands with a marking pen or Dykem to help you see where the ura is being ground down. Don’t ever guess.

Place the most pressure on the focus line selected above. Move the blade back and forth (not side to side) onto and off of the diamond plate, diamond stone or kanaban with the cutting edge and the focus line always touching the diamond plate or kanaban. Don’t go past the high point for now. Be careful to not grind a notch into the narrow side lands where they meet the edge of the diamond plate or kanaban. Most people make this mistake at first. Please don’t you make it more than once.

Grind the ura down so the line at the highest point and the cutting edge is fairly flat.

Remember, the narrow lands at the sides of the hollow-ground urasuki will abrade down quickly. And the rest of the ura can be gradually flattened during subsequent sharpening sessions using regular sharpening stones. It doesn’t need to be made perfect immediately. What matters most is the steel on the itoura land right at the cutting edge.

This flattening process is seldom required except on new blades.

Polish a blade’s ura up to the level of your finest finishing stone once, and don’t touch it with rougher stones again unless it is absolutely necessary, or further gradual flattening is required. This means that in normal sharpening sessions you must remove all the damage at the cutting edge by abrading the bevel with the rougher stones, and only when the bevel is ready for the finish stone, do you work on the flat or ura, alternating from bevel to flat/ura until all defects, burrs, and even visible scratches are polished away.

If you condition the flat (ura) side of the blade correctly, and keep it polished, you should not need to work it on anything but your finish stone until it is time to tap out and grind the ura or back in the case of plane blades. Therefore, the bevel side of the blade is where we spend most of our time and effort.

Now that the ura is in good shape, we will look at sharpening the other side of the wedge, the blade’s bevel, in the next post in the series. In the meantime, keep yer stick on the ice.

YMHOS

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Links to Other Posts in the “Sharpening” Series

• 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
• Sharpening Part 30 – Uradashi & Uraoshi