To obtain a sound proof structure capable of being mounted and dismounted with ease, and also installed on a ready-made machine by closely fitting detachably a cylindrical vibration attenuating member comprising a high hysteresis elastic body on the surface part exposed.
An upper flange cover 30 is mounted on the outer circumference of an upper flange 24. The upper cover flange 30 is closely fitted in the rear end outer circumference of a cylinder body 9 by its large diameter part 31 and on the outer circumference of the upper flange 24 by its small diameter part 32 respectively. Front cover assembly 35 is furnished with a bearing case 3, a first cylindrical cover member 36 to be closely fitted in the outer circumference of a drill head cover 2, an annular holding plate 37 for holding the first cover member 36, and a second cylindrical for covering the rear end of a cleaning swivel 17. The upper flange cover 30, the first cover member 36, and the second cover member 38 are made of nitrile rubber, and the holding plate 37 is made of resin. As such, a sound proof effect can be achieved without the need of enlarging the machine in size.
Uto, Masataka