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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?
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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.
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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!