| 摘要 |
PURPOSE:To prevent any bending moment from yielding on the bracket arm part by supporting a guide bearing with use of a member which is movable in the axial direction. CONSTITUTION:A thrust bearing 1 commonly provides a guide bearing 16 at the part of a thrust collar 5a. Besides, the thrust bearing 1 provides a plurality of bracket arms 1f which are extended outwards like the spokes of a wheel in the radial directions, furthermore these bracket arms 1f have cylindrical rings 1g at their outer peripheral parts, and they abut through the cylindrical rings 1a on the inner wall 3 on the outside of a bit. Thus, since the cylindrical rings 1g which have been provided at the tips in the radial directions of the bracket arms 1f are revolvable, movement in the axial directions of the bracket arms 1f is easily allowed, so that there is no cause of the bending moment attributable to the load of water thrust. |
