Deep boring of structual laminated wood for bolt joint

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Many wooden structures by structural lamineted wood can be seen in Japan recently. In this structure, bolt joint is adopted and many deep holes are bored with long drill. Some problems, for instance, the crook of bored hole and so on have been pointed out by manufacturing factory.In this work, after we made experimental apparatus, we examined about the crook of bored hole in the deep boring of structural laminated wood with long drill. From the experimental results, although the crook of this work material with the deepest hole of 300mm became larger as the feed per revolution became larger, the degree of it was small as compared with that of squared Douglas-fir timber. In the square Douglar-fir timber, the crook of bored hole became larger as both angle of annual rings to bore surface on cross section of wood and feed per revolution became larger and as the depth of boring hole became deeper. Hence it was concluded that the crook phenomenon of bored hole of structural lamineted wood was not affected by the angle of annual rings to bore surface on cross section of wood very much because this work material was made by laminationg bark side and pith side alternately. Well, as we confirmed in this experiment that the run out of drill's extreme during boring was affected by tool rigidity and the exhaust of chip became more difficult as the depth of boring hole became deeper, we want to design long drill with high rigidity and with smooth exhaust of chip.