Patent GB-566390-A (GB)
Title: Improvements in or relating to milling or like machines
IPC: B23Q35/18
Filed: 1943-05-20
Abstract: 566,390. Milling-machines. BRISTOL AEROPLANE CO., Ltd., BOLAS, J. T., and EDWARDS, R. W. May 20, 1943, No. 8046. [Class 83 (iii)] In a milling or like copying machine of the kind wherein the cutter is advanced to penetrate the work and then relative movement between the cutter and work in a closed path is produced by fluid pressure motors acting in two directions inclined to each other, the control valve for one motor being reversed by a rise in pressure of the other motor when its motion is stopped by contact of a feeler with the pattern or by other stoppage of the motor, a separate control valve is provided for each motor and the two control valves are actuated by four pilot valves under the direct influence of the fluid pressure in the motors. The shape of the work is produced partly by the shape of a pattern and partly by generating arcuate and straight portions thereon. As applied to milling out the curved radial passages m, Figs. 3 and 4, of a solid forging which is to form the rotor of a supercharger, the blank 10 is oscillated about an axis passing through d, Fig. 4, whilst an end milling-cutter 13 is machining the walls a and b, and is oscillated about a perpendicular axis passing through e, Fig. 3, as shown by the dotted line position, for machining the radial walls c, the cutter being fed continuously in an axial direction until the straight walls of the passage have been machined completely. The curved portion of the passage is then machined by an end mill 13, Figs. 5 and 6, the blank in this case being oscillated about an axis passing through h to traverse the cutter from i to j and moved radially to cause the cutter to machine the side walls c, the radial traverses decreasing in length as the cutter is fed down the curved inner wall k of the passage. For the first operation the machine, having the cutter 13 rotating on a stationary axis, is set up as shown in Fig. 7, the blank 10 being carried by a table 11 capable of oscillating about the axis d and mounted on a table 12 capable of oscillating about the axis e, these oscillations being effected by fluid pressure cylinders 14, 16 respectively. Fluid, which is preferably oil, but may be air, is delivered by a constant delivery pump 18 to distributing-valves 22, 23 controlling the flow to the respective ends of the cylinders. In operation, with the parts as shown in Fig. 7, the table 12 is fed continuously towards the cutter by a hydraulic motor (not shown), and fluid proceeds from the pump 18 by pipe 49, valve 23, and pipe 31 to the inner end of cylinder 16 to maintain the piston at the end of its travel as shown. Fluid also passes from the pump by pipe 28, valve 22 and pipe 29 to the inner end of cylinder 14, causing the piston 15 to rock the table 11 for machining the surface b. At the end of its stroke, the piston 15 abuts the end of'the cylinder and pressure in the system rises, whereby the supply by pipe 34 from valve 22 to a pilot valve 36 overcomes the pressure of the spring 46 to raise the valve and allow fluid to flow by pipe 44 to a plunger 27 connected to valve 23. This valve is then moved to the left, admitting fluid from the pump by pipe 32 to the outer end of cylinder 16 to advance the piston 17 and rock the table 12 for machining the surface c, the piston 15 remaining in its inner position to prevent rocking of the table 11. The piston 17 is stopped by its cylinder at the end of the stroke, pressure increases, and fluid in the pipe 37 leading from valve 23 to pilot valve 38 raises this valve and then passes by pipe 42 to piston 25 to reverse the valve 22 and move the piston 15 outwards for machining the face a. In a similar manner, using the pilot valves 35, 40, the pistons 17, 15 are actuated to complete the cycle and cause the cutter to traverse the four sides of the passage m, the feed of the table 12 along the axis of the cutter continuing until the curved portion of the passage is approached, as shown in Fig. 3. The diameter of the cutter is sufficient to remove all the metal at the narrower end of the passage, but a pyramid of metal is left at the centre of the wider end, which is removed by the second machining operation as shown in Fig. 6. For this second. operation a laminar pattern is used, having the same shape as the required passage and mounted to partake of the same motions as the work. The latter is mounted on a table adapted to rock about an axis corresponding to the axis h, Fig. 5, on a table carried by slides and moved to cause the cutter to traverse the radial walls c of the passage m, the rocking movement causing the cutter to traverse the arcuate path from i to j at one end of the radial traverse and moving the cutter from one wall c to the other at the opposite end. The rocking and traverses of the tables are performed by pistons similar to the pistons 15, 17 actuated in sequence by the valve arrangement shown in Fig. 7, the motions of the pistons being stopped by the sides of the pattern engaging a fixed stop corresponding to the cutter so as to cause the rise of pressure in the system which starts the succeeding motion 'and the work being fed continuously along the axis of the cutter. The two machining operations may be performed by a different set-up of the same machine, or separate machines may be used. A hand-operated valve 48, Fig. 7, is provided for connecting the pipes 29, 30 to cause the flow of fluid to the operating cylinders to be short-circuited and thus allow the tables to be adjusted by hand for setting up the work. Instead of using springs 46 for biassing the pilot valves 36 &c., low pressure fluid may be used, supplied from the pump 18 through a reducing valve 51 and pipe 52.