| 摘要 |
537,018. Screw-and-nut gearing. CINCINNATI MILLING MACHINE CO. Nov. 29, 1939, No. 31072. Convention date, Nov. 30, 1938. [Class 80 (iii)] To prevent backlash in a screw-and-nut mechanism for moving the work support of a milling machine &c. the lead screw is provided with a pair of nuts rotatable on the screw into engagement with opposite sides of a fixed abutment. The lead screw 13 rotatably mounted in the work support 12 passes freely through a fixed abutment 30 on opposite sides of which are nuts 32, 33 having bevel gear teeth 35, 36 meshing with a bevel wheel 37 having spur teeth engaging a rack bar 38 capable of a limited axial movement between fixed stops and pressed by a helical or rubber spring which normally urges both nuts into engagement with the abutment. When the table is moving towards the right under idle conditions or when the work is moving in the direction opposite to the direction of rotation of the milling cutter the nut 33 is the driving nut and the friction of the screw in this nut is greater than that in the nut 32 resulting in a preliminary slight turning of the nut 33 with the screw which through the gearing, turns the nut 32 in the direction to release its pressure on the abutment and thus the friction on the screw thread therein is released. When the table moves in the opposite direction the nut 32 forms the driving nut. When the table is moving e.g. towards the right and the work is moving in the same direction as the cutter for " climb " miliing, the engagement of the cutter with the work tends to move the screw axially increasing the friction between the screw and nut 32 and decreasing that between the screw and nut 33. The nut 32 turns slightly with the screw and, through the gearing moves the nut 33 towards the abutment. In this condition of working therefore, both nuts firmly engage the abutment. |
