Sharpening japanese style

[Chris Hall]

Going back to the illustration Sebastian showed in his last post,

be5bbcaa1082c2fde3672c47f5828a8d.jpg (43.09 KiB) Viewed 17343 times

The top of the picture asks:

引く力 x　回数 + 切り口良否

It's asking to compare, good and bad (良否), the tooth patterns shown with pulling force (引く力) and number of saw strokes required (回数).

Then there is some text below the illustration comparing tooth pattern 'A' with 'C'.

About 'A', the text reads:

Aの場合
■引っ張る力　鋸を引くときにCの３倍ほど力がいります。
■切り口　繊維を引きちぎるので、切り口が粗い
■鋸を引く回数　34回（Cよりも７回多い）

The first bullet point looks at how much strength is required to pull the saw, or hipparu-chikara (引っ張る力), and says that 'A' tooth pattern makes for 3 times the effort as compared to 'C'

The second bullet point looks at kiri-guchi (切り口), which means the end grain cut surface I do believe, and says that it will be arai (粗い), rough.

The last bullet point notes the number of strokes to cut the piece, at 34 strokes, which is 7 strokes more than with tooth pattern 'C'

About 'C', the text reads:

Cの場合
■引っ張る力　鋸を挽くときの力はAの1/3程度
■切り口　　光を放すようなカンナをかけたような光沢がある
■鋸を引く回数　27回（Aより7回少ない）

Well, this list is the mirror image of the list for 'A'.

The first bullet point looks at pulling load, and states that 'C' requires 1/3 the force.

The second looks at the end grain cut surface, and notes that is it bright, polished (光沢がある) and the fibers cleanly cut, like a plane made the surface work.

The last bullet point looks at number of cuts, noting that it took seven fewer strokes with 'C' than 'A'.

[Chris Hall]

There's also a drawing comparing 'C' with 'F', the only difference between the two being the angle of the uwame (tooth tip):

db488a4ae57152fcd19517b81610dd19.jpg (22.42 KiB) Viewed 17343 times

The text:

「CとFの下刃は同じ角度です。上目の角度を変えました。さてどちらが切れるでしょうか」

もうお分かりになりましたよね。悩んだ方は先ほどの防波堤をイメージしてください。

下刃の角度が同じ場合

刀の先端（上目）を尖らせないほうが、スーッと素直に切れます。答えはCです。Fの場合、切り口が波打ちます。

Below the illustration, the writer asks how the cutting might be different between the two uwame forms. He then suggests to think of the image of a breakwater (防波堤をイメージしてください).

He then states that if the cutting tip angle does not become so sharp (（上目）を尖らせないほうが、), then the cutting action is smooth and predictable, as in tooth 'C'. If tooth pattern 'F' is employed, the end grain cut surface will look rippled (nami-uchimasu 波打ちます)

[Sebastian Gonzalez]

Thanks a lot Chris!

I could not understand anything with google translate.

In my experience, I don't know if I can quantify as a factor of 3 the cutting force you need in one and the other configuration.

What I can attest, is that when you use little force the cut surface becomes noticeable smoother. Still not the level I would like it to, but it's improving. This is spruce from the construction market.

L1080028.jpg

The upper half of the cut was kind of pushing down the saw, while the second was with a really slight stroke, and fast. That way the sawdust seems to fly better and easier and you get a nicer surface.

Here a picture of boxwood, one half cut 3 months ago and the other last week or so.

L1080252.jpg

[Chris Hall]

Happy to help.

This slide compares the cutting action of a knife slicing cardboard at two different angles:

13.jpg (88.48 KiB) Viewed 17340 times

No need to translate as it is self-evident. If the knife is held at a more vertical position, as in (2), the cut surface is jagged - or boro-boro (ボロボロ). This demonstrates his point about having teeth sharpened at a negative rake, unlike disposable blade saws, where the tooth is sharpened at a positive rake.

[Paul Atzenweiler]

If I sleep with this web site on next to me will I wake up being able to translate Japanese? (please say yes)

[Sebastian Gonzalez]

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[Chris Hall]

I think we have a reversal of terms involving 'positive' and 'negative' rake. Going back to this diagram:

be5bbcaa1082c2fde3672c47f5828a8d.jpg (43.09 KiB) Viewed 17332 times

I would term 'A' positive rake, and 'C' negative rake.

In machining, it is the same use of terms for the different types of rakes:

rake.jpg (9.99 KiB) Viewed 17332 times

Another pic showing for saw teeth:

sawRake.jpg (2.45 KiB) Viewed 17332 times

And one for a (powered) crosscut saw blade:

DeWaltSawBladeTerms.jpg (9.13 KiB) Viewed 17332 times

So, given that 'C' is the ideal according Nakakatsu, it seems we are talking about a 'negative' rake, correct?

[Sebastian Gonzalez]

So, given that 'C' is the ideal according Nakakatsu, it seems we are talking about a 'negative' rake, correct?

That's correct, I always get confused. Maybe because you need to "push" the file towards the facet that I associate it with a positive. I will edit my previous post to be sure it's right. Thanks for pointing it out Chris.

[Chris Hall]

All right, good to be on the same page, please carry on...

[Sebastian Gonzalez]

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