Patent GB-575192-A (GB)
Title: Improvements in or relating to machines for cutting grooves, holes, slots or the like
IPC: B23D3/02
Filed: 1944-03-02
Abstract: 575,192. Shaping. BRISTOL AEROPLANE CO., Ltd., WHITEHEAD, F. W., BOLAS, J. T., and EDWARDS, R. W. March 2, 1944, No. 3934. [Class 83 (iii)] Tools.-In a machine for cutting deep grooves, slots, &c., bounded by four or five sides, a tool is reciprocated relatively to the work and is given an oscillating movement in the plane of reciprocation at the end of each or a number of the reciprocations to produce an end wall of the groove. To produce blind slots 16, Fig. 14, in a work-piece 15, a tool is used consisting of a group of blades 18, Fig. 13, one for each groove, having inclined end faces 18a, 18b provided with stepped cutting edges 19, the tool being reciprocated in the direction of arrow V from the position shown to deepen one half of the groove 16 by means of the face 18b, then oscillated to bring the face 18a into cutting position and simultaneously cause the end tooth 19a to cut part of the end wall 15c and then reciprocated in the opposite direction and oscillated into the position shown to cut the left-hand part of the groove. The blades in a group are of different widths so that slots of different lengths, as shown in Fig. 14, may be cut with the same stroke of the tool slide. An in-feed towards the base 15b of the grooves is given between each reciprocation and the tools are withdrawn completely or almost completely after each oscillation for swarf clearance, Fig. 12, being a diagram of the cycle. A machine for carrying out the process comprises a work carrier 23 attached to a hydraulic cylinder 66, Fig. 2, which is movable axially to and from the tools by a plunger therein attached to an end plate 62 of a casing 67 slidably supporting the cylinder, the casing being attached to a non-rotating screw 61 engaging a rotatable nut 59. The tools are carried by a transverse slide 26 reciprocated in a head 22 by a pair of hydraulic cylinders 27 and the head is oscillated about a vertical axis 24 after each reciprocation by a hydraulic cylinder 25 whose piston carries a rack driving an arcuate rack 75 on the tool head through toothed gearing. The hydraulic supply from a pump to the cylinders 25, 27, 66 is controlled by valves operated by pneumatic plungers whose, control valves are actuated by solenoids energized and released by switches operated automatically by the work and tool movements so that the machine repeats the operative cutting cycle until the desired depth of grooves has been reached and then comes to rest. In operation, the cylinder 66 is advanced towards the cutters until a switch thereon is closed by a stationary contact on the work head 21 and on manual closure of a starting switch highpressure oil is delivered by the pump to cylinder 66 to advance the work to the tools (l, Fig. 12). When the work reaches the required position, contacts on the cylinder 66 and casing 67 are closed to admit high pressure oil to cylinders 27 to reciprocate the tools on a cutting stroke (m, Fig. 12), the cylinder 66 being maintained in its forward position by hydraulic pressure, and on the termination of the cutting stroke switches on the plungers of cylinders 27 are actuated to supply high-pressure oil to cylinder 25 to rock the tool head 22 about axis 24 (n, Fig. 12). Switches on the tool head then reverse the hydraulic supply to cylinder 66 to withdraw the work from the tools for swarf clearance (o, Fig. 12) until contacts on the cylinder and work head are closed to again reverse the flow and advance the work to the tools for the next cutting stroke (p, Fig. 12). The latter is started by the work-head contacts and terminated by the tool-head contacts (q, Fig. 12), after which the tool-head is oscillated (r, Fig. 12), and the work withdrawn for swarf clearance (s, Fig. 12), to complete the cycle. During the withdrawing movements of the work (o and s, Fig. 12), the electric contacts which institute these movements also actuate pneumatic valves which control a hydraulic circuit to admit high-pressure oil to a cylinder 44, Fig. 4, whose plunger carries a rack 42 engaging a toothed segment 41 carrying a pawl 45 meshing with a ratchet 46 on a shaft 39. The latter is connected by a dog clutch, bevel and worm gearing to the nut 59 so that at the commencement of strokes o and s the pawl 45 will be oscillated in the idle direction, whilst prior to the strokes l and P the pawl will be oscillated forwardly to rotate the nut 59 and advance the casing 67 by an amount equal to the depth of cut so that the contacts carried thereby will be advanced a corresponding amount and allow the tools to penetrate further into the work before the stroke is terminated and the lateral reciprocation started. The dog clutch may be disconnected to allow the shaft 39 to be rotated by a hand wheel for adjustment of the work, or a hydraulic motor connected to the shaft 37, Fig. 2, driving the nut 59 may be brought into action for advancing or retracting the casing 67 and the work rapidly, an interlock being provided to prevent simultaneous actuation of the hand and power feeds. When the grooves have been cut to the required depth, the arrival of the casing 67 at this advanced point opens a switch which causes the machine to be stopped at the end of the next withdrawal of the cylinder 66. A master switch may be operated manually to disconnect the automatic circuits controlling the solenoids for operating the pneumatic valves, each solenoid then being under pushbutton control by the operator, and this position of the switch operates a valve to put the hydraulic pump on low-pressure delivery. The hand lever for operating the switch is also connected to a valve which controls the pressure of the hydraulic supply or cuts it off, within the manual control range of the switch, so that the speed of movements under push-button control may be varied. The hydraulic motor for moving the cylinder 66 rapidly to and from the tools is supplied with low-pressure oil only and the valves in the circuit are arranged so that when the cylinder is fully withdrawn the motor can only be rotated in the advancing position and vice versa. The limit switches on the work head for controlling the cycle of operations are adjustable by screws, and the side faces 18f, Fig. 13, of the tools may also be stepped to produce grooves having their end faces 15c of stepped formation in addition to the bases 15b. The Provisional Specification describes a machine in which a casing equivalent to the casing 67 is moved to and from the working position by a hydraulic cylinder operated from the low-pressure supply from the pump under control of a manually-operated valve which also controls two low-pressure cylinders for clamping the casing at the working position. After clamping and pressing a starting switch, the machining cycles continue automatically until the required depth of grooves has been reached, the working motions being supplied with high-pressure oil from the pump, and when machining is completed the pump is automatically changed to low-pressure supply ready for withdrawal of the work and casing by the operator. In this machine, withdrawal of the work and cylinder 66 for swarf clearance is only performed after a number of cutting strokes instead of after each one, a switch being provided which is rotated intermittently through ratchet mechanism by the tool slide so as to close contacts which control the withdrawal only after the required number of cutting strokes has been completed.