PURPOSE:To remarkably improve the life of a band saw blade as well as to reduce noises and vibration during a cutting time by a method wherein a guide space of band saw blades is automatically adjusted in an optimum guide stage in accordance with a variation of a cutting length of a material to be cut in the cutting time. CONSTITUTION:A horizontal band rotates and drives a driving wheel 13 by means of a rotation driving device (motor) and makes a band saw blade 23 stretched between the driving wheel 13 and a driven wheel 12 travel and drive to cut off a material M to be cut off. Next thereto, the change of a cutting length is detected during a cut-off working of the material M to be cut off by means of a detecting device 43 and this detected value is fed back to a driving device 37 through a driving control circuit 47 to control and then, the distance between a guide brackets 33 and 35 is sequentially adjusted. With this, the guide space between the saw blades 23 is automatically adjusted in an optimum guide state, in accordance with the variation of a cutting length of the material M to be cut off, accordingly, the life of the blade 23 is remarkably improved and at the same time, the noise and vibration during a cutting off time is reduced.
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