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In this video I demonstrate thinning a Takeda Gyuto which the customer felt was too thick for his tastes. Another knife sharpener refused to do the procedure, feeling that he could not do it without messing up the finish. He felt the knife was too thick and should be returned to the maker or vendor who sold the knife to him. The customer asked if I could do something with his knife and this is the result..
When I received the knife, I found that the knife was in excellent condition as a new knife and would be more than adequate for most customer's tastes. It was a very well crafted knife. But the customer wanted it thinner.
So I proceeded to thin the knife using a series of 'finger stones', taking care not to mess up or damage the kuroichi finish, something the 'other' knife sharpener felt he was incapable of doing.
The stones used included some coarse Nubatama stones followed by some fairly soft stones. I started with some Nubatama synthetic stones 150, 220 pink, and 400 grit and then switched to Kyushu Ohmura coarse natural stone, 1200 Nubatama, Yaginoshima Asagi and finally Hideriyama. I stropped this final edge on Kangaroo leather.
As a test of it's performance, I sliced a piece of Ginger using a slice cut, using only the weight of the knife with no additional downward pressure. The final edge is an excellent combination of sharpness produced by this refined geometry from thinning the blade, a natural stone finish which imparts a finish having a degree of toothiness and refinement enhanced by the kangaroo leather to give effortless cutting performance.
If you use a 5k stone after I finish it on a natural stone, it will convert the finish to the 5k stone finish. So if the 5k stone were a Shapton, it would completely remove the natural stone finish. The 5k Nubatama would be less drastic, but really utilizing a natural like a Yaginoshimsa Asagi or a Hideriyama would be the way to go.
Mark and everyone else who responded to this thread - Thank you for the kind remarks. Coming from my 'sharpening peers', it means a lot to me.
That a certain 'sharpener' (no one on this board FWIW) refused to do the knife thinning on this knife due to a lack of skill on his part made this all the more interesting of a challenge.
I chose a fingerstone approach rather than using an EP or even a Gizmo (which I have and used to make). The Gizmo allows me to go down to zero degrees, but sometimes knives that are forged in the style of Takeda or Moritaka have high spots that might be hit at these acute angles, damaging the kuroichi finish. Using full sized stones and freehanding it almost guaranteed that thinning the edge would scratch up the kuroichi finish. Utilizing fingerstones was the answer for this task. Because the shape is irregular, softer stones were required along with initial coarser stones. So stones like the 150 220 and 400 Nubatama Bamboo stones did the heavy work of removing the finish and thinning above the edge. To get a uniform finish, the softer 1200 Bamboo and 2k Ume black stone - aka the Olive brick of joy - were perfect. I preceded these two stones with the NATURAL Kyushu Ohmura stone, which converted the scratch pattern of the coarser Nubatama stones to a natural stone finish. The 1200 Bamboo and 2k olive brick of joy maintained the finish contrast beautifully, allowing me to continue on to using the Yaginoshima Asagi and finally a Hideriyama fingerstone. A final stropping on Kangaroo left a natural stone style of edge but with a bit more refinement. The 1200, Ohmura, and 2k were perfect for producing a uniform finish, underscoring how well these Nubatama stones work with natural stones.
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