Patent GB-527477-A (GB)
Title: Improvements in or relating to backlash eliminating mechanism for machine tools
IPC: B23Q5/56
Filed: 1939-04-13
Abstract: 527,477. Milling-machines &c. CINCINNATI MILLING MACHINE CO. April 13, 1939. No. 11210. Convention date, April 25, 1938. [Class 83 (iii)] [Also in Group XXIV] A machine tool such as a milling-machine has relatively rotatable members such as a screw and nut for operating a slide at a speed controlled by a hydraulically-actuated clutch, and backlash-eliminating mechanism comprising an auxiliary member engaging the screw or nut and actuated to take up backlash by hydraulic means responsive to the position of the clutch. The machine has a column 11 carrying a cutter spindle 12 and having vertical guides for a knee 15 which in turn has guideways for a work table 17. A power shaft 21 is connected by bevel gearing 22 and vertical shaft 23, to a shaft 25 connected through a gear 27 on a parallel shaft 28 with a high-speed gear 48 loose on a sleeve 43. The shaft 28 is also connected through gears 29, 30, shaft 31, change gears 32, 33, gears 35, 36, sleeve 37, and gears 38, 39, 41, 42 to the sleeve 43 which also carries another drive member 44. The gear 42 and member 44 are connected to gears 45, 46 respectively through overrunning clutches 47 both these gears being thus driven in the same direction at feed rate. The gears 45, 46 are geared directly and through an idler respectively to gears 59, 62 loose on a sleeve 60 carrying a splined reversing- clutch 66, the sleeve being secured on a shaft 61 connected by gears 69 and further gearing to the rotatable feed screw 75. The high-speed gear 48 is formed on a clutch member which may be engaged with either of the gears 45, 46 to cause that gear to overrun its feed drive and the shifting of clutch 66 will give a slow feed speed in one direction and a fast traverse in the other direction. The clutches are actuated by shifters such as 58, Fig. 5, moved in either direction by hydraulic cylinders 56, 57. When fluid is admitted to both cylinders, the reversing clutch 66 is neutralized'and the table stops. When the clutch is in neutral, the table may be operated manuallv from the handle 84. The table screw 75 runs in a nut 86 fixed to the knee. When a down cut, Fig. 11, is used, the table tends to overrun. In order to eliminate backlash when down-cutting an auxiliary non-rotary nut formed as a piston 88 is threaded on the screw and is advanced by hydraulic pressure to move the screw bodily to take up the backlash before the cutter engages the work. The piston 88 moves in a cylinder 89 controlled by a valve 99 connected by passages 100, 101, to ports in the cylinders of the speed control clutch yoke 58. These cylinders are in connection, Fig. 11, with ports in a pilot valve 112 to which pressure fluid is supplied from a pump 114 through a line 118. The pilot valve also controls the fluid supply to a stop valve 122 controlling the supply to the cylinders of the reversing clutch fork 76. The pilot valve has both axial and rotary movement and its trip plunger 119 co-acts with dogs on the table. When the pilot valve connections cause the plunger 53 and speed clutch 48 to move to the left the reversing clutch being in the Fig. 11 position the table moves to the left at high speed. In this position part 55 cuts off the supply to the backlash cylinder so that the take up mechanism is ineffective during this movement. During the leftward movement a dog 153 engages under a lug on the pilot valve plunger and shifts the pilot valve so as to give the connections shown in Fig. 11. Pressure is now admitted to cylinder 56 moving clutch 48 to the right so that gear 59 is driven at feed speed. In this position, pressure flows through a groove 109 and lines 101, 97 thus moving cylinder 88 to the left and taking up backlash in the direction of the table feed. As the table approaches the end of its feed a reversing dog 158 engages projection 149 on the pilot valve and rotates it to give the connections shown in Fig. 9. Pressure fluid now flows in line 108<SP>1</SP> and shifts the reversing clutch 66 to the right, and as the clutch gear 48 is already in its right hand position the table is reversed at high speed. The pressure port 106 is also closed so that the backlash eliminator is ineffective. If the table is required to travel at feed speed during its movement to the right another dog on the table actuates the pilot valve to admit pressure to line 137 and shift the speed clutch yoke 58 to the left. The line 108<SP>1</SP> is now connected to the left hand end of the backlash cylinder to render this mechanism effective in the proper direction. The table may be stopped manually or automatically by shifting the stop-valve 125 so that fluid is admitted to both the cylinders 82, 83 to neutralize the reversing clutch. A latch 162, Fig. 6, engaging a shoulder on the plunger is withdrawn by a dog 164 which depresses a spring plunger 165. Thereupon pressure in a chamber 172 moves the valve to the left. The plunger is reset bv a member 176 rotated from a hand lever 174. This lever is also used to cause a projection 178 to disengage the latch for manual stopping of the machine.