Patent GB-448376-A (GB)
Title: Improvements in milling or like machines for copying or reproducing
IPC: B23Q35/18
Filed: 1934-12-05
Abstract: 448,376. Milling-machines; valves ; hydraulic transmission of power. FITZPATRICK, H. J., 94, Hope Street, Glasgow.-(Clearing Machine Corporation ; 6499, West 65th Street, Chicago, U.S.A.) Dec. 5, 1934, No. 27619/35. Divided out of 448,337. [Class 83 (iii)] [See also Group XXIX] In a copying milling or like machine a tracer and cutter are mounted on a support moved to-and-fro relative to the pattern and work in harmony with pressure variations in a single-acting fluid cylinder controlled by the tracer, constantly acting means exerting a counter-force in opposition to the fluid cylinder, and a governor is provided controlled by the tracer to vary the supply of fluid to a traversing cylinder in order to adjust the speed of traverse of the tracer and cutter parallel to the pattern and work in accordance with the steepness of variations in the pattern. The machine comprises a base 1 provided with guides 3 for a carriage 77 traversable parallel to the pattern 8 and work 9 (i.e. at right angles to the position shown in Fig. 1), a slide 74 being movable vertically on the carriage and carrying the tracer 14 and cutter 39. The tracer is attached to a stem 20 carrying a disc 34 engaging a valve 23, and a plate 24 on the valve is held against a seat 26 in a cylinder 18 by means of an adjustable spring 15. Pressure of the pattern on the tracer causes the disc 34 to displace the valve to the right in Fig. 1, thereby allowing fluid to flow from an inlet 27, past the seat 26, through an aperture 32 in the valve and then by an outlet 61 to the sump 62. This reduces the pressure in a cylinder 58 on the same supply line and containing a piston 64 connected by a yoke 65 to the tool spindle 42, thereby allowing a weight 72 to withdraw the cutter and tracer through a cable73. Relief of pressure on the tracer allows the spring 15 to close the plate 24 on the seat 26, stopping the flow of fluid through the valve and causing the pressure in the cylinder 58 to rise and overcome the weight 72, thereby pressing the cutter and tracer to the left. The cutter is rotated by a splined bevel gear 47, bevels 57, a speed reduction box 56 and a motor 55. The carriage 77 is traversed by a piston 84 in a fixed cylinder 85, the fluid being led to opposite sides of the piston by passages in the piston rod 82 which are connected to supply and exhaust ports in a valve 88 on the carriage. The valve is reversed automatically at each end of the traverse by dogs 6, 7 on the base 1 engaging a load and fire lever 92 thereon. Fluid is supplied from the sump 62 by a pump 67, one branch leading by pipes 68, 86 to the valve 88 and cylinder 85 and another branch 69 leading to the tracer cylinder 18 and a governor valve G. A piston 157, Fig. 2, in the valve G has a slight clearance with an annular rib 156 and is normally maintained opposite the rib by two adjustable springs 168, 169. An enlargement 164 on the stem 160 attached to the piston 157 has an annular groove 165 which normally provides a passage for the fluid from the pipe 68 to the pipe 86 and then to the cylinder 85. In operation, with the carriage 77 traversing along the pattern and work, if the tracer is passing over a flat part of the pattern or a part having slight undulations, the amount of fluid flowing to and from the cylinder 58 is nil or very small, and this small quantity may flow from the pipe 69 between the piston 157 and rib 156 without displacing the piston, and thence by the pipe 60 to the cylinder 58. This will allow the carriage 77 to traverse past the work at a uniform rate. If the tracer encounters a large protuberance on the pattern, however, the valve 23 will be forced considerably to the right in Fig. 2, a large quantity of fluid will flow through the valve and the pressure in the cylinder 154 and pipe 60 will fall. This will allow the weight 72 to withdraw the cutter from the work and force a large quantity of fluid from the cylinder 58 through the pipe 60, cylinder 154, and valve 23, causing a sudden surge through the cylinder 154 which will displace the piston 157 to the right. The annular groove 165 will then throttle the passage of fluid to the cylinder 85 and reduce the speed of traverse of the carriage 77 until the protuberance has been surmounted, or may stop the traverse completely. If the tracer encounters a deep depression in the pattern the valve 23 will close completely, the supply from the pipe 69 will build up the pressure in the cylinder 154 and fluid will flow rapidly through the cylinder and pipe 60 to the cylinder 58 to feed the cutter towards the work, thereby again causing a surge past the piston 157 which will move it to the left and throttle the supply to the cylinder 85. The speed of traverse of the carriage will thus be reduced if the tracer and cutter have to surmount any large cavities or protuberances so as to allow time for the cutter to remove the required amount of material from the work. The pattern may be of soft material such as plaster of Paris, whilst the work may be hard material such as metal. Further description of the machine, including reversing means for the carriage 77, step feeding means for the slide 74 and operation of the valve 23 by the tracer, is given in Specification 448,337.