To realize a forcible oiling with a simple constitution by providing an oil sump for storing oil in a bearing and an oil circulation passage for recovering the oil supplied from the oil sump in the bearing via a spiral oil groove to the oil sump.
An upper shaft 31 is rotated by a motor in the direction of an arrow and oil is supplied to a ring-like groove 29 from an oiling port 90a of an oil sump 90 via an oiling pipe 27 and a spiral groove 26 made on the upper shaft 31. Since the ring-like groove 29 is connected to the right end 26b of the spiral groove 26, the oil supplied to the ring-like groove 29 is always supplied to the spiral groove 26 irrespective of the rotation angle of the upper shaft 31 and is spread on the inner surface of a bearing 24a and most of it flows to the stem-side end of the bearing 24a from the left end 26a of the spiral groove to thereby form a suitable oil film between the left end 26a of the spiral groove 26 and the inner left end of the bearing 24a and to absorb a vibration. Then, the oil is introduced to the oil sump 90 from a recovery hole 90b through a recovery pipe 28.
OTA EIICHI
MOMOTOME TAKAO
