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  1. #1
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    Default Ura-oshi method. Have I screwed up my new chisel

    So Im a timber-framer and I have only until recently used European style framing chisels. I was taught to place the entire backside of the chisel on the stone (parallel with the long edge of the stone) and flatten it as an initial step towards its first sharpening.

    So guess what I did when I bought my first Japanese tsuki-nomi? - I did just that. After trying to flatten it for a minute or so on a 400 grit wet-stone, I looked on the back (ura) and noticed that my stone was only cutting on the very front (cutting edge) and the very rear (near where the blade transitions to the neck.) The chisel appeared very uniformly convex (not only the hollowed portion, but also the entire edge of the blade from cutting edge to neck.) Now this was an expensive chisel made by a well known blacksmith, so I couldnt help but think it was made this way for a specific reason. I immediately stopped trying to flatten it in this way so as not to completely screw up a very expensive tool. I know the purpose of the hollow oval on the back, but what is the reason for the convex axis of the entire blade?

    IMG_4629.jpg

    Through some online investigation, I've gathered that I should be flattening the back of Japanese chisels by holding the blade perpendicular to the cutting edge and only removing very slight amounts of steel on the sides of the back (the long lines on either side of the hollowed oval.) and that this convex axis should be maintained. I feel like I screwed it up and the beauty of this expensive tool has been diminished. Perhaps its not so bad, and Im just trying to be overly perfect since I want my sharpening to be on par with the handmade beauty of the chisel.
    tsuki_edit.jpg
    So what would a Japanese tool expert do here to reconcile this and bring it back to its ideal state?
    Thanks for your input. I appreciate it very much!

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  3. #2
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    Default

    I'm far from an expert, but I believe any "damage" done is almost purely to the aesthetics. It's just not as pretty now.

    It may flex slightly more in use - by 1% or so - but I'm quite sure that neither you nor I could detect it.

    Probably the best thing you can do for it now is simply use it. Correct sharpening under normal use will bring the leading edge back to dimensions soon enough and age will restore a patina to the bright steel, making it less noticeable. You could try applying a surface finish to "hurry up" the patina, although personally I wouldn't. Especially not a chemical process.

    As far as I know, the reason for the convex profile is to add strength while still using the minimum of steel, a prime example of the japanese attitude of making the best use from few resources.

    Use it, enjoy it for what it is. If I've guessed the right maker, it's still a very, very nice bit of kit. Bruised, but not broken.
    I may be weird, but I'm saving up to become eccentric.

    - Andy Mc (AKA "Ghost who posts." )

  4. #3
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    Default

    Thanks for your reply. Yep I guess just use it as it supposed to be used, learn my lesson and carry on. If you can still tell the maker, I guess I haven't scarred its appearance too much.

  5. #4
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    As Andy has said, "bruised but not broken".

    Unless you are going to be selling the chisel any time soon and to a J-tool expert who might know and value the difference, no significant damage has been done, IMO.

    Just to get things into perspective, here is a link to an image showing the ura on a well used set of Ichihiro chisels that have been reconditioned by a J-tool expert. http://www.japan-tool.com/zc/images/Tsuki-Ichi01.jpg

    As I understand it, the purpose of the ura is to minimise the effort and time required to sharpen the very hard steel on the non-bevel side side of the blade. Keeping the surface area on this side to a minimum speeds up sharpening.

    Blades will warp as the tension between the hard and soft steel is released. So, some flattening is needed on most blades when you first receive them. The longer the time between forging and flattening the more this may be required. Also, chisels that are used like a slick (sashi nomi) do need to be flattened along their full length to maintain blade cutting angle. The challenge is to keep the surface area behind the cutting edge to a minimum width while doing this.

    One thing to check for is that you haven't removed enough metal from the neck end so that the handle is now coming into contact with the flat surface created by the back of the chisel. If this is the case the handle will push the blade off vertical as you cut your mortises. The handle should sit proud of the surface like this:

    https://www.workshopheaven.com/media...ng-Slick_3.jpg

    Relax and enjoy your new nomi.

    N.


    PS - Once flat, I tend to use use only my finer stones to remove the burr and to maintain the ura side of my J-chisels so the surface area behind the cutting edge is kept to a minimum. Although it is quite some time since I have had any of them out and on a stone.
    Stay sharp!

    Neil



  6. #5
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    Default

    Hi Neil, I much appreciate your comments, information, and shared links. Yes I think now with some perspective the 'over grind' is quite trivial. Ive checked and there is no issue with the neck contacting before the blade back.

    So I understand the purpose of the concave hollow on the backside of the chisel and the advantage that offers us towards maintaining a keen cutting edge easily. However what I was wondering about was the sort of camber the chisel has (if I place the chisel on a flat surface - such as the back of my diamond lapping plate in the photo - it only contacts the plate near the cutting edge and where the blade meets the neck, as you can see the light shining through quite well.)
    IMG_4739.jpg
    So youre saying that this camber is actually unintentional, and is the product of movement between the high carbon steel layer and the softer iron it is laminated to? and this is perhaps because the chisel sat unused for such a long time after it was forged?
    So ideally, on a slick chisel (tsuki-nomi) like I have here, the back should be completely flat and no light should be visible like what I have in the photo? Right now the narrow edges that were traced in my first post do not contact the stone at all when the full length of the blade is above the stone.
    Attached Images Attached Images

  7. #6
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    herynkc You are right that no light should shine through between the back of the chisel and the diamond plate.

    A chisel should be Co-planer in its length, excluding the hollow in the centre. If the back is concave in its length like yours then your chisel will work in much the same way a bench plane with concave sole producing a convex surface.

    I was helping a friend cut a mortice with an old chisel he had - time and time again he would undercut his mortice sides. Each mortice had a distinct belly in its middle and undercut at the bottom. For a while I was perplexed until I happened to notice that the chisel had a noticeable concavity in its length like yours.

    You have 3 options:

    Use a fine stone #4000 plus. Then working the full length of the blade until no more light can be seen. You should be able to preserve most of the hollow if you work carefully. It does not matter to much if the narrow edges / sides (legs) of the back get say 2mm wide on either side. All that matters is that the ura is symmetrical and the ura is preserved.

    Or send the chisel to a blacksmith or a skilled metal worker. With careful skill I have seen them peck a chisel by applying tension in such a way that that blade bends straight. But you need to know what you are doing. Itís the same trick they use to straighten bent backsaw.

    Or if you bought from a reputable dealer then show them the problem and ask for a replacement.

  8. #7
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    Quote Originally Posted by herynkc View Post
    So ideally, on a slick chisel (tsuki-nomi) like I have here, the back should be completely flat and no light should be visible like what I have in the photo?
    Yes, for the reason Thumbsucker has given.

    The exception is an intentional slight convex curve on the back that some joiners put on a second slick towards the cutting edge so that they can reduce the mortice size a bit at the deep end of the mortice. This second slick is used primarily for this and the occasional bit of surface planing the way a yariganna is used; the depth of cut is controlled by rocking the blade (up or down/in or out) on the convex back face.
    Stay sharp!

    Neil



  9. #8
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    Default Bend it or grind it?

    Thanks for your reply thumb. What a bummer. I bought it second hand. The person who sold it to me had is for 4 or 5 years but never used it, but he told me the back had been flattened already. Which is why I was perplexed when I started polishing the back and it was hitting exclusively on the front and back of the blade. what a bummer. So I guess my initial attempt to flatten the back wasn't incorrect at all.

    I dont think there are any replacements of these available as the maker doesnt seem to produce these any longer. So I guess my options are have it back bent or grind stone it down.

    How would a blacksmith be able to back bend this without heating it and destroying the temper? I do have a 1 ton arbor press. Perhaps I could shim up the ends of the blade and apply delicate pressure on the center of it until it flattens?

    If I were to follow your suggestion of grinding it with a 4000 or finer, it would probably be best to apply more pressure on the cutting edge end than on the neck end of the blade? - this way I think the ura-suki would be a bit more uniform in shape.

  10. #9
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    Default

    Do not try to using a press or anything to straighten the chisel yourself. You will FUBAR the chisel possibly causing it to crack and delaminate. Donít do it.

    Later today I will post photos of how to flatten a chisel back. Just hold.

  11. #10
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    Here Are some photos of the motion used to flatten the back of a Japanese chisel. It has the following advantages:

    Since the bevel end spends most of the time on the stone through the stroke the bevel end is worked the most - protecting the legs (narrow sides) with less grinding. It also brings the back inline co-planer with the front section of the back. It distributes wear evenly across the surface of the stone. It avoids the possibility of adding a step / shoulder into the back.

    2CA9C5C2-C26E-411B-8A40-5C1936434BB0.jpeg C31EC592-7E4E-45FA-B513-AFC1A651E41F.jpeg B28B899D-D0DE-41D3-9D16-45E19801AC71.jpeg 31C597AF-47DA-474C-9B38-52F1CC4FAB33.jpeg D745633D-B2FF-4FB0-8142-23D7823BC04E.jpeg 4FB3651A-EF1B-44FB-BB91-252A9E857CF3.jpeg

    I hope it makes sense- itís moving left and right in short strokes rather then long up and down strokes most people use. Note that the back tang part of the chisel should never touch the stone. Pressure should be biased towards the tip not the tang but do not lift the handle as you will back bevel the chisel and gouge the stone.

    This method was taught / recommended by both Stu from tools from Japan and
    David Charlesworth.

  12. #11
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    Interesting method. I appreciate you sharing it with me. Iíve never tried flattening that way. So since the cutting edge area touches the stone for the entire stroke while the opposite end only touches it momentarily, you are essentially slanting the plane of the back very slightly.

    My chisel is much longer than the one in your photos however. I would need to do this along the short side of the stone to ensure continued contact of the cutting end for the entire stroke.

    The only bad thing about doing that is the distance between my cutting edge and ura-suki (the back hollow) will be pretty large. From what I understand, the smaller this distance is the better. Therefore, I would have to grind my bevel back considerably to lessen this and have the best cutting action with this tool. It may be a lot of wasted steel if I do this all at once, I may just have to use it with a concave back and with each sharpening work it out.

    Iím still really surprised the steel bent itself in this fashion simply from sitting around and releasing tension between the lamination. But I guess it is the same concept as when I weld a rectangular frame clamped to a table and release it only to find out that it doesnít stay in the shape it was clamped. Simply because one of the 4 joints was welded hotter than the other 3 it creates an unbalanced tension. I guess even steel is more organic and unstable than we like to believe.

  13. #12
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    Red face

    You are working on a very fine stone #5000 plus the amount of material removed is minute and will not substantially increase the flat area at the front of your chisel. Even if the front area of the chisel is bigger then 2mm is the chisel will still work just fine and it will not going make sharpening exponentially more difficult.

    You will never maintain or achieve this ideal ura examine any used nomi and the ura are in all sort of states. None exhibit perfection most have odd shaped hollows bulging legs and flats that are far from ideal. It is this state of decay and imperfection in which the beauty of the tool is to be found.

    There is theoretical perfection and then practice neither are ideal states. We must just muddle through.

    One thing that I appreciate about Japanese tools is that their state of un-becoming moving from a state of being to non-being. To quote Tyler Durden ďyou do not want to die without scarsĒ they mark your passage through this life.

  14. #13
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    Thumbsucker. Rule #1.

  15. #14
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    So it sounds like the larger flat area is no issue here. It will probably end up being more like 5 or 6mm after flattening. But I suppose a few mm wont matter.

    Quote Originally Posted by thumbsucker View Post
    None exhibit perfection most have odd shaped hollows bulging legs and flats that are far from ideal. It is this state of decay and imperfection in which the beauty of the tool is to be found.
    Im down with the wabi-sabi concept of finding beauty in the imperfections, so i am with you. My chisel doesnt have to be perfect.

    I simply ask these questions here to learn the ideal way to sharpen a Japanese chisel. The ideal of course will never be met and the product will always come out flawed. Though if you dont have high goals and well founded understandings you'll attempt something and never get close to high end results. For example, when Im laying out timbers to 1/32" tolerance then Im hoping that after they've all been cut, pre-assembled and raised there is a 1/16" resolution in the end.

    I do appreciate the information youve shared very much Thumbsucker. I hope to get involved in more discussion on this forum moving forward.

  16. #15
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    Quote Originally Posted by herynkc View Post

    I hope to get involved in more discussion on this forum
    That would be good. Most of the current participants are cabinet makers and the like. A timber-framer would add another dimension. A I understand it, most of the continued use of traditional Japanese tools in Japan is by temple, shrine and tea house builders/re-builders, with a few exceptions like kumiko screen makers. I'm sure a timber framer will bring a similar perspective to the forum.

    Best practice may aim to have the ura extending out close to the edges, but in practice it eventually just shrinks away. Viz, this well used old Fujihiro.PS - that misty finish is fresh off my finest Nakayama stone. I do like using this one for paring around some convoluted woodturned bowl forms that I make, but that level of finish is well beyond what would be beneficial on a building site.
    Stay sharp!

    Neil



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