Patent ID: 6863232

Claim:
A tape tension controlling mechanism for controlling a tension of a magnetic tape when the magnetic tape is run for recording or reproduction of a signal thereto or therefrom by a magnetic recording/reproducing apparatus, comprising: a reel bed which engages, and integrally rotates, with a tape reel around which the magnetic tape is wound; a reel bed drum which rotates integrally with the reel bed during recording/reproduction of the magnetic tape; a tension post around which the magnetic tape is looped with a predetermined angular distance; a tension arm including the tension post and rotatably supported by a tension arm shaft; an urging element for rotationally urging the tension arm in a rotation direction; a tension band, one end of which is connected to the tension arm, and which has an engagement portion at the other end, the tension band providing a rotational moment to the tension arm in a direction opposite to the rotation direction of the tension arm, such that the magnetic tape is looped around the tension post with a predetermined angular distance; and a band fixing screw for fixing the other end of the tension band, the band fixing screw having a threaded portion at one end thereof and a head portion at the other end for preventing disengagement of the tension band from the band fixing screw, the band fixing screw further having, between the threaded portion and the head portion, an intermediate shaft portion for engagement with the engagement portion of the tension band, and a tapered portion smoothly extending between the intermediate shaft portion and the threaded portion; wherein a longitudinal center line of the intermediate shaft portion is shifted from the longitudinal center line of the threaded portion, a pitch P of a thread of the threaded portion and a longitudinal length L of the intermediate shaft portion have a relationship of L>P/2, the threaded portion of the band fixing screw is an external screw thread which is screwed into an unthreaded resin hole; the threaded portion and the unthreaded resin hole have a relationship of D 1 >D 2 , where D 1 denotes the diameter of a circumcircle of a ridge of the threaded portion, and D 2 denotes the diameter of an inscribed circle of the unthreaded resin hole; and the tapered portion, as the band fixing screw is screwed into the unthreaded resin hole, smoothly extends through the engagement portion allowing the intermediate shaft portion to be securely engaged with the engagement portion.