Patent GB-651280-A (GB)
Title: Improvements in or relating to tracer head mechanisms for copy milling machines
IPC: B23Q35/36
Filed: 1948-02-23
Abstract: 651,280. Copy-milling machines. CINCINNATI MILLING MACHINE CO. Feb. 23, 1948, No. 5276. Convention date, March 12, 1947. [Class 83 (iii)] . A tracer head for a copy-milling machine comprises a housing 10, a control valve 58 movable in the housing and a pilot valve 60 movable in a ported bore of the control valve by means of a universally-mounted tracer 43 so as to control and balance pressure which acts on both ends of the control valve to determine its position. The tracer housing, Fig. 2, is mounted for vertical and horizontal adjustment by means of feed-screws on a support 15 by which it may be fitted to a tool slide. The tracer arm 43 is supported about midway along its length by a spherical portion 35 engaging a seat in an inner sleeve 32 which is slidable in an outer sleeve 28 attached to the housing. Deflection of the tracer arm about the pivot 35 is converted into axial movement of a sliding member 47 by means of a ball 46 and, through a spacer rod 61, the pilot valve 60 is moved within the bore of the control valve 58 which slides in a valve sleeve 54. A spring 38 balances the weight of the pilot valve; tracer arm and associated operating parts. To adjust the valve settings initially, the spring 38 is first adjusted by,a nut 39 screwed in the sleeve 28 so that a flange 65 on the tracer arm just rests on the outer sleeve 28, a spring 64 is adjusted to give a small downward pre-load on the pilot valve and then the valve sleeve 54 is adjusted by means of a set-screw 56<SP>1</SP> until a port 91 is above a land 92 on the control valve. Pressure from a pump 67 is supplied through a line 70 to a space 72 above the valve 58 and through a channel 74<SP>1</SP> to a wide groove 76 in valve 58 and thence to a wide groove 79 in the pilot valve 60 and back through a port 113 to a return line 115. The pressure is throttled at ports 77 and 81 in the main valve so that the pressure in the groove 79 is half the full pump pressure. By connecting the groove 79 through a channel 84 to a space 85 below the valve 58, where the area of valve exposed to pressure is twice that of the corresponding area at the space 72, the valve 58 is stabilized with respect to the pilot valve. A stop and start valve 102 is fitted between the tracer head and a piston 110 which is connected to a tool and tracer slide 112. When the valve 102 is moved upwards from the position shown in Fig. 3 to the stop position, in which it is held by a detent 116, fluid is directed from the pressure line 70 through ports 117 and 105 to the lower side of piston 110 and moves the slide to its uppermost position ; fluid displaced from above the piston returns through ports 106 and 119 to the return line 115. When the valve 102 is moved down to the start position, fluid passes through the ports 91 and 95 in the valve sleeve 54, and through ports 99 and 106 in the valve 102 to the top side of piston 110, to lower the slide 112 until the tracer engages the pattern and raises the valve 60. This decreases the throttling effect at ports 77 and 81 and the increased pressure raises the valve 58 until the port 91 is closed. A rise on the pattern will then raise valves 60 and 58 and so supply pressure through port 96 and valve 102 to raise the slide 112. The work and pattern table may be fed in transverse directions by feed-screws 123 and 124 and, to prevent the table being moved so that the tracer might be broken by an obstacle, the valve 58 has an over-deflected position in which pressure is supplied from the groove 76 through a port 127 to plungers 129 and 130 which engage toothed wheels 133 on the feedshafts and prevent their further rotation. When the valve returns to a normal position, the fluid-pressure leaks through a resistance 132 to the return line 115.