uradashi depth

[correntinos]

hi everybody , I m trying to made japanese tools , I want to know the depth of the uradashi and if the ura have the same depth in al the blade ( and if have diference betwen ura of kanna and nomi

thanks a lot

javier from the other side of the world

[Sheets]

Kanna usually have a constant depth (except right at the cutting edge, where it tapers to nil). I checked a few of my kanna and the depth of the ura was from a scant .25 mm on one to about .75 mm on one with the deepest ura. The others were in between.

It makes sense to have the depth of the ura as shallow as possible so that when ura-dashi is needed, there is not a big distance to move the steel. It makes sense too, the wider the kanna, the deeper the ura (assuming that the radius of the grinding stone is constant). If the smith uses a sen to make the ura, he would have more control over the depth and could make it shallower even on a wide blade.

Nomi have an ura that gets deeper toward the tang. This is so doing ura-oshi regularly as one sharpens, the ura does not disappear due to the increasing depth. Since doing ura-dashi is not an option except on fairly wide nomi, so the deeper gradient prevents the ura from meeting the edge.

I checked some of my chisels, and the ura depth goes from about .2 mm near the edge to about .5 mm at the shank (I'm guessing at the depths because it is difficult to measure).

I don't know how they vary the depth along the length given the constant width, unless they grind the ura at a constant depth and then taper the blade? Anyway, for you to figure out, Javier (and let us know).

Steve

[correntinos]

thanks a lot sheets fpor your answer its very useful for me , I never see a japanese tool

thanks a lot again

javier from the other side of the world