| 摘要 |
844,697. Lathe and like centres. ROHM, G. H. Nov. 28, 1956 [Dec. 19, 1955; Jan. 7, 1956], No. 36442/56. Class 83 (3). A lathe &c. live-centre comprises a tip 2 rotatable in a housing 1, and movable axially therein against the work, by fluid under pressure in a cylinder C, a relief-valve 37 to allow the passage of fluid from the chamber at a predetermined adjustable pressure, and means 40, 41 to return the fluid when the pressure in the chamber falls below the predetermined pressure. An annular piston 10 in the cylinder C supports the tip 2 through a thrust-bearing 7 and the inner axially-slidable race 6 of a rollerbearing 4, and is normally out of contact with return springs 13, 14, and a stop-shoulder 11 on the inner wall of the cylinder. A plunger 20, in a passage leading to the cylinder C, is controlled by a spring 21 and a screw 22 to control the fluid-pressure in the cylinder, and carries a rack 20 engaging a pinion 23 for operating a fluid-pressure gauge. This may be of the clock-type, having the finger rotated by the pinion-shaft 24 or, as shown, comprise a linear-scale behind a transparent panel and over which an indicator 31 is moved on an endless-cord on pulleys 28 driven by gears 26, 27, from a gear on the shaft 24. The reliefvalve 37, Fig. 2, is forced against its seating by springs 43 compressed by a plug 44 moved by a graduated knob 46 engaging screw-threads 45 on the plug, which is held against rotation by a pin 45a. In a modification, Fig. 8, the passage of fluid through the relief-valve in the return direction is assisted by a spring-loaded piston 51 in the bore 50 of the valve, fluid entering the bore 50 through passages 53. Operation.-The knob 46 is turned to load the valve 37 to the desired relief-pressure, and the screw 22 turned to adjust the fluid-pressure to a value corresponding to the minimum permissible force on the point. The centre is then moved against the work until the reliefpressure is achieved in the fluid. If the fluidpressure increases, as by expansion of the work, fluid passes behind the relief-valve along grooves 38, 39, in the valve, and is returned to the cylinder, past a spring-pressed ball 41 in the valve, when the pressure falls. |
