帯鋸歯の片あさりがひき曲がりに及ぼす影響

Abstract

帯鋸の片あさりがひき曲がりに及ぼす影響を調べるため, 鋸の内側と外側とであさりの出の異なる厚さ0. 9mm, 幅102mmの4本の鋸を用い (図1, 表1), 長さ600mm, ひき幅50mmと100mmのホワイトセラヤとペイツガをひき材し, 帯鋸に作用する力, 鋸身の変形とひき曲がり量を測定した (図2, 3)。鋸に作用する力のうち主分力, 送り分力の鋸による差はなかった (図4, 5)。横分力はひき材開始時から大きいあさりの出の方向に作用した。その結果, ひき道はあさりの出の大きい側に曲がった。あさりの出の差が0. 47mmの鋸2の最大ひき曲がり量 (理想ひき面からのひき面の最大偏差) は, 0. 26mmの鋸1の2倍以上であった (図7)。これは鋸2の横分力が鋸1よりも大きかったことや, 鋸2の片あさりによる送り分力の力学的な作用点の鋸身の厚さ方向の中心からのずれが, 鋸1よりも大きく, 鋸身をねじるモーメントが大きかったためと考えられる。また鋸4のあさりの出の差は鋸3よりもわずかに小さかったが, 横方向の剛性が鋸3より小さかったため (表2), ひき曲がり量は鋸4のほうが大きくなった (図8)。また横分力は被削材の繊維走行の影響も受け, 鋸が被削材の繊維走行に沿ってねじれる方向に発生し, その結果, 繊維定行方向と送材方向のなす角度が大きくなるほどひき曲がり量も増加した (図6)。

To examine the influence of an unsymmetrical set in the handsaw teeth on the deviation of the kerf, white seraya and western hemlock boards (600mm in length, 50 or 100mm in sawing height) were sawed with four bandsaws (0.9mm thick and 102mm wide) in which the saw teeth were set unsymmetrically (Fig. 1, Table1). The force acting on the saw, the deformation of the saw, and the deviation of the kerf were measured (Fig. 2, 3). There was no difference among the saws in the force components in the cutting or the feed directions, respectively (Fig. 4, 5). The saw teeth were pushed laterally towards the side with the larger set. As the result, the kerf bent in the direction of the larger set. The maximum deviation of the kerf from the inteded sawing line for saw 2, which had a difference in set of 0.47mm was more than twice that for saw 1, which had a difference of 0.26mm (Fig. 7). The larger deviation for saw 2 (relative to saw 1) was due in part to the larger lateral force component for saw 2 and in part to the larger torsional monent for saw 2. This torsional monent was caused by a shift in the point of action of the force component in the feed direction, away from the center of the saw blade. This shift, in turn, resulted from the unsymmetr ical set. Saws 3 and 4 had almost the same difference in the amount of set. However the deviation of the kerf for saw 4 was larger than that for saw 3 (Fig. 8), because saw 4 was less rigid than saw 3 (Table. 2). It is also clear that the lateral force component was so exerted that the saw was twisted along the grain of the work. As the result, the deviation of the kerf increased with the angle between the grain direction and the feed direction.