Posted by Hello and welcome to my blog! The process of tapping out, known as ura-dashi, is unique to Japanese tools and most commonly used on plane irons. This post will focus on the efforts I’ve made to chase after an effect of careful ura-dashi maintenance known as Ito-ura or thread edge.
Japanese tools are made for the user to easily create a very sharp edge, their design and construction provide for that once they are properly set up. It’s the setup part, however, that presents some challenges and can be daunting at times. Once those steps are completed, the regular maintenance of a properly setup blade is very easy so long as it is performed as needed.
Japanese tools are constructed of hard steel (hagane) laminated to soft iron (jigane), the iron often being very old wrought. Initially one might perceive this interest in old wrought iron as being purely aesthetic, but with regular maintenance of many tools comes an appreciation of those plane irons which feature a nice old wrought for more than just their looks, but because old wrought iron is usually very malleable. Chisels on the other hand are not normally backed with very soft iron, instead the smith will work toward a balance between strength and ease of maintenance.
Japanese tools feature a hollow, known as urasuki, on their back or ura. The ura is maintained through a process known as ura-dashi. The goal of ura-dashi is to expand the jigane with hammer blows until the hagane deforms. This deformation is what ultimately allows for a thin landing at the cutting edge and also allows the landing to be maintained throughout the life of the tool.
The chisels shown here are a displaying the result of both tapping out and slowly changing the bevel angle (higher). The chisel on the right is further along in the process. These chisels are by Hidari Konobu, the head blacksmith Saitou-san prepares his tsuki-nomi in a way which makes them similar to plane blades in that they can be setup and maintained with ura-dashi. In other words, these are not normal chisels and I do not suggest using ura-dashi on regular chisels except in rare circumstances on wide chisels.
Initially upon tapping out, with success, the steel will begin to form a new landing. As the landing is blended into the remainder of the uraba it begins to become uniform. The left again contrasts the right in that the right side is further along.
The goal of ura-dashi is to form a landing in a way which can maintained with ease and one which presents the furthest tip of the cutting edge to the stone. If this is not done, or if the landing is made very large, the tip of the cutting edge will be recessed from the stone and the burr created from sharpening never quite removed. The result will be a semi-sharpness that will be unimpressive. One way to guarantee that the extreme edge is on the same plane as the rest of the landing is to create an effect called ‘ito-ura’ or thread edge. Ito-ura is a situation in which the landing is very thin and so contacts the sharpening stone without failure.
During regular use of a chisel or plane blade the blade wears on both the bevel side and the back side to form the rounded profile of a dull blade. On the backside of the plane iron this is known as a ‘wear bevel’. The wear bevel is just that, a bevel, and will not contact the stone when the back is placed flat on the stone. Instead of wearing away at the back to remove this, the bevel is reduced until the wear on both sides of the iron are removed. The flatness of the contact surface on the back then becomes critical in effectively removing the burr, any part of the back which is out of flat will cause the landing to be uneven and so part of the burr will be retained. One way to ensure that the backside is perfectly flat is to have a very small contact area which is maintained only by the finish stone, the finish stone being one which is kept absolutely flat.
This is very similar to maintenance of western blades by hollow grinding the cutting edge, the hollow allows a thin contact point at the front and back of the cutting edge. Those two contact points, being very small will wear quickly and evenly to form a thin landing that is even and flat.
Earlier this year I spoke with Jim Blauvelt, an experienced tea house carpenter and blacksmith, who recommended some changes in my ura-dashi routine. Jim suggested that I revisit using the corner of my anvil’s surface and he also suggested that I change the shape of my hammer’s face. The face I was using was a hard edged square face, and Jim suggested reshaping that in the shape of a cross peen hammer. The result would be that each hammer blow would be more effective and that it would create a rounded divot rather than a sharp divot.
Rather than trying to position my blade on a rounded corner of my anvil, I decided that it was time for a support that would be much more intuitive to use. My father offered up a hardy insert for the anvil. I polished it up and prepared it for use. The original surface hardness long gone and what remained is soft iron. I thought it might be hardened, as many of these tools are, but it dents very easily and so likely the hardening has been removed from misuse in it’s previous life in a high school metal shop.
I repaired the surface, not only for aesthetic reasons but because I do not want rust transferring from the tool to the back of the plane iron.
It was time to once again proceed with ura-dashi. The first patient, one that had presented some difficulties. The blade simply would not budge with the previous process, and so the improvements made allowed it to move predictably. Eventually I created a very thin landing.
A little more ura-dashi.
And the final result, ito-ura, or thread edge.
Now having realized ito-ura, I’ve been chasing that effect in my other plane blades. The resulting sharpness from ito-ura is markedly improved over the same edge and a wider landing. Many plane blades arrive from the maker with a land already too large to really be considered ito-ura. I’ve taken to carefully working the ura to ensure that the landing does not increase drastically which would put the goal of ito-ura even further away. The first step in doing this is similar to how I did the work previously. Using my granite checking plate to search for teeter-totter.
The low side then being shimmed up and raised by carefully working the center of the blade to deform the soft iron and reposition the steel so that it seats along the entire outside landing.
The ura is then marked, and the rubbed on the granite check plate to see where the landing contacts. Shown here the landing contacts very far behind the cutting edge. If one were to start flattening the sides would grow dramatically before the back would become flat making for difficult future maintenance of this blade. However, I will proceed with ura-dashi and work the blade until the cutting edge touches along its edge before using a sharpening stone.
Once the blade shows contract evenly along the edge, based on my sharpie marker test, the blade is then brought to the finest sharpening stone and the back worked lightly until an even finish results. The result is a thin edge around the landing, rather than a thicker edge that would result from working the the blade from a low grit stone on up.
The thicker edges, on the two blades shown on the right for example, are being slowly worked back until a thin thread edge remains.
Given enough regular use and sharpening the edge will begin to recede showing inconsistencies in the landing. As the edge disappears those spots will be tapped out and eventually the remaining landing will be very even and thin. This landing is thinner in the center, and so it will be worked with a bias toward the center until the landing is both thin and straight across. It will take many sharpening sessions but over the course of those sessions it will improve.
I hope that you have enjoyed reading this post and I look forward to your comments. My regular work will proceed very soon. I’ve been building pieces which I’ve covered in detail in the recent past and so I’ve decided not to write about them specifically. Once completed I will finish up my shoji shortly there-after and detail the steps taken in completing the shoji work.
Wonderful post! It would be even more complete if you would add a diagram showing in reference to a blade all the terms.
Thank you Martin, I may well do that.
Very interesting post.
Thank you!
Thank you for sharing your techniques and the details of this process.
Thank you! My pleasure.
This was a great read thanks Brian, I also like the blog’s new look. Very clean and organised.
Thanks Salko! Appreciate your feedback on the format as well!
Hi Brian!
Your blog it’s a treasure. It’s very kind of you and generous to share all this splendid info since there’s poor and few information about japanese handtools and woodworking in other languages than japanese. I have enjoyed and learnt very much and I am sure too many people around as well. Your anvil insert is really nice and seems very convenient. I use a typical small anvil, I also round the tip of my funate gennou which I employ for Ura-dashi. I usually hit lower the bevel than you, maybe my poor technique or the type of steel in my blades. Briefly, awesome post as usual!
My best wishes
Hi Hayabusa,
Thank you, I appreciate the encouraging words and I will certainly keep at it. While I do maintain my interest in 18th century western tools it would seem the bulk if my interest is in Japanese tools. They’re simply enthralling.
Hitting a little lower is fine, I tend to aim right for the middle or err on the side of caution and stick with the upper bevel, depends on how well I know the blade.
Fantastic post Brian! I will keep my blade backs hidden in shame. LOL. Seriously tho, this is something I really need to tackle. Frankly I’m very nervous about attempting the tapping out process. I just got these planes working well, the last thing I want to do is crack a blade. Your post almost gives me the confidence to give it a go…almost. 😉
Thank you! Being a little nervous, or rather cautious is probably a very good thing. It’s initially unnerving but gets much less so over time and with a little success. You might want to pick up some flea market blades to give it a go until you feel comfortable working on your everyday blades.
Very nice write-up Brian! I’m interested in the method of working the middle of the Ura with the piece of wood to get the landing thin and even. To what extent can this be done with old blades, that have wide “legs” from extensive flattening of the back? Or is it only for the finest adjustments? It would be interesting to see a video of the process, to get an idea of the force and duration needed. Do you know any references?
again, thanks for taking the time!
Oskar
Hi Oskar, That part is simply where I am straightening the blade and removing any warpage which will start things off in the wrong direction. I would expect that old blades that have wide legs have already been worked flat but you could certainly check them.
I enjoy following your exploits. After putting my tools aside for a time, it encourages me to get back in the game. FYI – looks like you have an old stake from Casting Specialties. More info on the Ganoksin/Orchid website.
Aloha
Hi Karl, Thank you for commenting, glad to hear that my work is encouraging you back to the shop. Thank you for the information on the stake!
Cheers
Brian
Thanks Brian. I agree, that if the legs are wide, then the blade is probably without warp, as a consequence of flattening the back. My thought was, that if one can hammer a warped blade flat, then maybe one can also hammer an old, ground out blade in order to make the ura deeper, i.e making the lands thinner. I imaging putting shims along both edges of the blade, and hammering in the middle. But maybe this is not possible, or stressing the blade too much ?
Hi Oskar, That part of the action doesn’t really move the hollow, it’s removing a few thousands of an inch of warpage from the blade. I would not recommend trying to pound the hollow deeper, you will likely crack the blade as that is not really the intended bit of that process. If the legs are wide, very wide, you can sometimes have the hollow reground. You might contact So and ask him to recommend someone to do that sort of work as I know he has contacts in Japan that can do it.
thanks Brian! I see now the difference between that minimal warp correction an a renewal of the ura. I have to see how the blade looks when it arrives. Its always interesting to follow your work, and I’m already looking forward to your next post!
My pleasure! Excellent, glad to hear that my comments added perspective. Best of luck with the new blade.
Brian,
I was shopping (well looking) at William NG site and found the Ura-Dashi hammer and had no clue what it was for and your blog came up as one of the first in my Google. I don’t know a lot, just enough to be dangerous as far as Japanese wood tools go and had no clue what that hammer was about until I read your excellent article on it. So my understanding is you are shifting the white (or blue) steel hard edge by striking above the weld line on the wrought iron to very gently make micro movements on the hard edges to even them out as part of the sharpening process? I think this is a process that m must be taken in a class to achieve proper understanding of exactly what a person with no knowledge on the subject is doing. My gosh, I as an un-educated type could really F up a beautiful chisel or plane with the best of intensions. Thank you for sharing your knowledge with us.
PatrickB
Hi Patrick, Thanks for your comment. You are expanding the soft iron by tapping out and in turn that will cause the hard steel to curve downward. I run classes on this topic, Happy to help get you on the right track.
Reading your blog above makes me realize how little I know about my Japanese plane blades (I have two.), and how much there is to learn. The info is not easy to find and that’s what makes yours so valuable. Where did you learn all this!? It’s very good of you to share it and to take the time to produce such good photos and clear and concise text. Inspiring, too! Thanks for your generosity, Brian. Regards, Bill
Hi Bill, Thank you, Ive learned from a large number of sources and from my own experimenting in addition to that. Chris Hall, Stan Covington, Jim Blauvelt, So Yamashita and Des King have all provided me with a lot of information and help in my search. I also attend Kezurou-Kai annually and have learned a ton of the finer points from Andrew Ren and Jude Noteboom, both of whom are just absolute magicians with a plane.
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