I've taken advantage of some extra time at home to tackle sharpening my usuba, which has been in need of attention (few small chips on the edge). It was bought about 10-12 years ago, unknown maker but it was the house line from Union Commerce in Tokyo, cost about JPY200,000 (so it's not the greatest) and is shirogami 2 from memory. The blade road had/has one flat spot on it, which I've lived with for a while. This, in conjuction with the chips, lead to me to want to try to flatten it out, raise the shinogi line and put a new edge on. I've sharpened it before a number of times but it hasn't seen heavy use and only minorly touched the shinogi line to date. I'm not a master with single bevel knives, but have used a deba regularly at home (e.g. weekly - we eat a lot of fish!) for a over 10 years, plus yanagiba too, so have a fair bit of experience sharpening these.
The usuba is a slightly different beast due to the thinness of the blade... The specific problem I have with it is as follows. I hit the shinogi line with a 400 grit stone and got quite a bit of the flat spot out, the shinogi line raised a bit (and relatively flat still). But I noticed (using a sharpie) that the extent of the sharpening along the blade road has formed a "smile". I.e. at the centre of the knife, I've got the blade road almost flat to the hagane and a little beyone and only maybe 3mm away from touching the edge, while at the tip and heel, it extends only barely to the limit of the jigane. That's not an issue in itself I don't think, but I also notice (and this could have been the result of imperfect technique earlier on) that at the heel and the tip, when I move to sharpening the edge, I have to noticeably torque the handle to increase the bevel angle to be able to adequately sharpen the edge and raise a burr. Whereas, at the middle, I just have to apply pressure with my fingers to hit the edge, without any noticeable increase in angle. The ura is in good condition; the edge itself is straight (I know this can be a problem with usubas due to the thinness). I've sketched a couple of pictures to illustrate this.
How do I fix this? My inclination is to keep raising the shinogi line until the hole blade road is flat, then put a convex edge on using the hamaguri technique at the end. But my concern is that, in doing this, I'm going to be altering the blade profile (i.e. this will imply removing more metal from the edge at the middle, relative to the tip/heel). Before taking drastic measures and really screwing things up, I thought I'd check first! Would really welcome any advice.
The usuba is a slightly different beast due to the thinness of the blade... The specific problem I have with it is as follows. I hit the shinogi line with a 400 grit stone and got quite a bit of the flat spot out, the shinogi line raised a bit (and relatively flat still). But I noticed (using a sharpie) that the extent of the sharpening along the blade road has formed a "smile". I.e. at the centre of the knife, I've got the blade road almost flat to the hagane and a little beyone and only maybe 3mm away from touching the edge, while at the tip and heel, it extends only barely to the limit of the jigane. That's not an issue in itself I don't think, but I also notice (and this could have been the result of imperfect technique earlier on) that at the heel and the tip, when I move to sharpening the edge, I have to noticeably torque the handle to increase the bevel angle to be able to adequately sharpen the edge and raise a burr. Whereas, at the middle, I just have to apply pressure with my fingers to hit the edge, without any noticeable increase in angle. The ura is in good condition; the edge itself is straight (I know this can be a problem with usubas due to the thinness). I've sketched a couple of pictures to illustrate this.
How do I fix this? My inclination is to keep raising the shinogi line until the hole blade road is flat, then put a convex edge on using the hamaguri technique at the end. But my concern is that, in doing this, I'm going to be altering the blade profile (i.e. this will imply removing more metal from the edge at the middle, relative to the tip/heel). Before taking drastic measures and really screwing things up, I thought I'd check first! Would really welcome any advice.
