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Size of Ura in a Japanese plane

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Size of Ura in a Japanese plane

#1

Size of Ura in a Japanese plane

paul womack

>I have a vague memory that Odate stated something like the following:

"it is common knowledge that planes work best when the ura (?the flat cutting part of the blade) is as small as possible"

Can anyone confirm that he said this (or its gist)?

Can anyone confirm that it's true, and in what contexts. AFAIK Odate worked in shoji, which (again, AFAIK) implies straight grained soft wood. I know that some Japanese work is done with hardwoods, but I don't know wether Japanese work include the Western fascination for strongly figured grain.

I have some thoughts on the consequences of Odate's statement, but I'd like to confirm my axioms before I proceed.

BugBear

Re: Size of Ura in a Japanese plane

#2

Re: Size of Ura in a Japanese plane

Pam Niedermayer - Austin, TX

>From page 150 of the hard cover "Japanese Tools...":

"The back surface of a Japanese blade is unique in that the flat between the hollow and the edge of the blade is extremely narrow. It is common knowledge among shokunin that the blade performs best just when this flat is narrowest."

In other places in the book he mentions that when purchasing a blade, the ura should not be too wide. I've misplaced my copy of "Making Shoji...", can't verify what, if anything, he says there about the ura.

Pam

Re: Size of Ura in a Japanese plane

#3

Re: Size of Ura in a Japanese plane

paul womack

>Thanks for confirming my memory. Of course, shoji are made from straight grained softwood (AFAIK), so his statement may be (implicitly) restricted to that context.

BugBear

Re: Size of Ura in a Japanese plane

#4

Re: Size of Ura in a Japanese plane

Pam Niedermayer - Austin, TX

>Could be, but it's not an assumption I'd feel comfortable making, especially since the smoothers work so well on all the North American domestic hardwoods such as cherry, walnut,...

Pam

Re: Size of Ura in a Japanese plane

#5

Re: My thought

paul womack

>OK; I'll outline my thought.

We'll take as an axiom that a Japanese plane works best with a small Ura.

Ignoring speculation as to why, what is the geometry of the cutting edge?

Given the existence of the hollow, the cutting edge is initially defined by the bedding angle; the ura.

However, very soon (in both distance and time terms) the shaving encounters a surface at a lower angle, as it enters the hollow.

I suspect the (claimed to be desirable...) change in behaviour would occur as the size of the Ura approaches the thickness of the shaving, otherwise the transition between the 2 surfaces (ura and hollow) would be too far away from the worked surface to have any effect via the agency of the beam strength of the shaving.

Is there a point to BugBear's ramblings I hear?

Yep. I think a low angle plane, bevel up, could be easily gset up to emulate this. All you do is grind the primary bevel at the desired (emulated) angle of the start of the hollow, and then put on a tiny (micro) bevel at the desired cutting angle to emulate the ura.

Sounds intriguing.

BugBear

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