スクレーパー　パート2

   「 Fixtures and Chucks for Woodturning Clarence Green 」(2011) を書いたClarence Green 氏こと、ドク・グリーン(グリーン博士)のホームページにスクレーパーについての詳しい説明がありました。パート2。

   スクレーパーのベストなベベル角度は、76°である。 一般的にベ一般的にベベル角度が大きいほどかえりは高くなるが 、別の要素で76°が適当だと思われる。

    ツールレストに刃物を置いた時 、60°ならば、刃先が木材に当たってしまいキャッチを喰らいやすい。76°ならばまずべべルが木材に当たり、そして取っ手の下を徐々に上げていくと、刃先が木材に当たるいわゆるべべルラビィングとなり、スムーズな刃さばきとなる。

   それに、底辺を4にして高さを1とする時、角度は14°になり、76°はそこからすぐに導き出せるので、便利だ。

The Best Bevel Angle

Opinions vary as to what the included angle between the bevel and top face of a scraper should be. An often suggested value is 70°. Some use angles as low as 60°. My preference is 76°, but I don’t fret if it varies a degree or two.

The burr will be stronger at higher angles but other considerations come into play. One is that clearance must be provided under the cutting edge so the heel of the bevel does not make contact with a concave surface like the inside of a bowl.

At a relatively low angle such as 60°, inadvertently lowering the handle may cause the cutting edge to dig into the wood. Also, my impression is that the lower angle makes the tool harder to control. For a larger angle like 76°, lowering the handle will cause the bevel to begin to rub the surface and lift the cutting edge out of the wood.

Why did I choose 76°? First I gravitated toward the higher angles based on the strength of the burr and the bevel-rubbing aspect which I consider important for new turners. Then it became a matter of geometry and convenience in laying out the angle. If you go over 4 and up 1, the resulting angle is 14°. This translates to 76° if you measure in the other direction.

シアースクレーピング

スクレーパーを45°傾けてカットする方法をシアーリングカットという。まことにスムースな仕上がり表面が得られる。

Shear Scraping

With this method the scraper is not laid flat on the tool rest but is rotated to an angle of 45º or more. This brings the cutting edge more in line with the approaching wood so the wood encounters the edge at an acute angle instead of 90º. This is called a shearing cut and the method is known as shear scraping