Hi dburnard!
Sorry it's taking me so long to get back to your email, but like I wrote I wanted to take time replying to that one, so give me a bit more time!
Let me just answer these for now.
I think the answer to both questions are basically the same and YOU have given me the answer yourself, so I'm gonna cut and paste it!:D
You were saying that "I would think that as a curved blade is tapped in to the dai, the blade would tend to dig out the grooves to match the curve of the blade" and that's exactly correct. Hahaha, you have answered instead of me:)
Then you said "In order to make a dai to fit such a blade it would need to have the grooves cut to match the curve of the blade - and I've never seen anything like that before." but I think you have! Every dai should be like that because the groove is cut to match the curve by the blade itself like YOU have suggested!
It is thus very important not to touch (shave, file, cut) the upper part of the slot yourself, but let the blade do the cutting. You adjust the looseness of the slot by shaving the Omote-najimi(the surface where the front side of the blade touches. Front side is the side without the mei=brand.) I will write an detailed article on how to set the blade into the block for the first time, soon(?)
Yes, this is a good "helping question" for further understanding my above article. Thank you!Quote:
Q2: So when we refit an old blade into an old dai, how much of the curvature should be removed before refitting the dai? In your drawings it only looks like you tried to remove a portion of the curvature. For some blades the curvature is small enough (only .002inch/.05mm or so) that removing it all is no problem - or it's so small that it should just be left alone. However on other blades the curvature is large enough (0.5 - 1mm) that removing all of the curvature at once would significantly alter the ura-suki, could make the hagane very thin at the edge, and noticeably change the taper of the blade so it may become loose in the dai, perhaps requiring a new dai. What would you suggest?
The intention of uraoshi is not to make the ura flat in order to match the dai, but to gain enough flat surface so that you can maintain the flat contact between the steel and the stone. (Someone help me out with the English here!!) If there is only 5mm of flat area, it is very difficult to keep it apressed onto the stone flat, so you'd need about at least 2cm. The amount depends on how curved the steel is.
If the curve is great, and this was the case with my drawing being exagerated, you can only grind off a little, because as you have explained you'd be grinding so much and loosing the ura-suki=the hollow. And you don't want to bend it any further either, thus you need to keep the ura-dashi minimal. And as you use it you gradually grind off the blade side of the ura and try to increase the flat surface. You start off from 1 in the below drawing, and by the time you've sharpened your blade, uhhh I don't know 100 times? you'd be at the #2 line, and #3 when you have sharpened 300 time! The below drawing is super exagerated to make it easier to see.
http://www.geocities.com/soatoz/phot...hi/SHARPE4.jpg
You need to press the blade side harder, and try to kind of lift the other side (called kai-saki, the lamination line) a little without actually lifting it up, creating more pressure on the tip of the blade and less on the kai-saki side. By doing so you can avoid looking like B in the above article.
http://www.geocities.com/soatoz/phot...hi/SHARPE5.jpg
If the curvature is just a little, basically you can flatten the whole steel part. Again you need to press the blade side harder, and kai-saki side lighter.
Thanks for the question. I hope I have answered your question well enough.
Talk to you soon.:)