Patent GB-1088892-A (GB)
Title: Contour cutting machine
IPC: B27B25/00
Filed: 1965-04-12
Abstract: 1,088,892. Copy-milling. CONTINENTAL MACHINES Inc. April 12, 1965 [April 13, 1964], No. 15500/65. Headings B3B and B3K. [Also in Divisions B5 and G3] A method of feeding a workpiece to a cutting tool, such as a band saw or end mill, wherein the cutting action takes place along a fixed, relatively narrow, straight cutting zone to produce a cut along any prescribed contour line, comprises using a controllable variable speed reversible power source to move a workpiece along a first path to produce a known force between the workpiece and cutting tool, supporting the workpiece for free movement in either direction along a second path which transversely intersects the first path, which paths are in a plane normal to the cutting zone of the tool, so that substantially zero force exists at all times between the workpiece and tool along the second path, rotating the workpiece about an axis which is perpendicular to the plane containing the paths for effecting cutting along a given contour, the rotation either adding or subtracting to the known force between the workpiece and tool along the first path, sensing any change in the known force, and utilizing the sensed change to automatically control the power source to maintain a constant force between the workpiece and tool along the first path whereby the cutting is effected at a constant rate along any contour by controlling only the rotation of the workpiece. In a band saw machine for carrying out the method, a band saw 14 is entrained about pulleys in a C-shaped housing 12 which supports a worktable 15 for movement along ways parallel to the flat sides of the saw band, a slot 16 accommodating the saw band, and corresponding to the first path. The top of the table is provided with anti-friction devices 17, Figs. 2 and 3 or lubricant to permit free movement of the workpiece WK over the table. The workpiece is turnable to permit the saw band to follow the contour by a flexible chain 18 disposed about the workpiece and a sprocket 19 rotatably mounted on the table and connected by gearing 23, 24, 25 to a shaft 22 having a hand wheel 21. The table is movable along the ways by a hydraulic cylinder 26, Fig. 3, controlled by a servo-valve 46 when fluid pressure is supplied to one end of its spool under the control of a selector valve 35, the pressure at the end of the spool being determined by a regulating valve 43. The other end of the spool of valve 46 has a rod (49) abutting springs (50) which support a sensing element (48) engaging the back edge of the saw band 14. In operation, the fluid force acting on the end of the spool is determined by adjustment of the regulating valve and acts to press the element against the saw band and to position the spool such that the fluid pressure supplied to motor 26 moves the table 15 with a constant force so that the saw band cuts the workpiece. When the workpiece is rotated by operation of the handle 21, the force applied by the workpiece to the saw band varies- and the sensing element 48 is moved to cause consequent movement of the spool of valve 46 so that the fluid pressure supplied to motor 26 is also varied to maintain the force acting between the workpiece and saw band at a constant value. The workpiece moves freely over the table 15 so that there are no side forces acting between the saw band and workpiece in the direction of the second path. In another embodiment in which the rotation of the workpiece is controlled automatically from a template and follower, the frame of the machine carries a pair of primary carriages 60<SP>1</SP>, Fig. 6, movable in the directions of the first path along ways 61, 62 by hydraulic cylinders 28. A secondary carriage 63 is movable transversely of the primary carriages in the direction of the second path along anti-friction guideways 64. The secondary carriage is in the form of a plate having two holes through one of which passes the saw band 14, Fig. 9, and aligned with each hole is a rotatable turret 66. The turrets are connected for rotation by a gear 20, Fig. 14, meshing with ring gears 71 on the turrets, one of the ring gears being driven from a variable speed, reversible, motor 72, Fig. 9, through a belt drive. One of the turrets is formed with a ledge 79 for receiving adjustable bars 78 for supporting the workpiece WK and the other turret has a ledge 80 supporting a template 86 which may consist of a pencil or ink line 85 on a sheet of paper. The template is positioned above a light source and a follower 83 above the template consists of a lens 89, Fig. 10, and a prism 90 which, when the line 85 of the template splits the light beam directs the images on to mirrors 91 and photo-electric cells 92 in the circuit of servo-amplifier 94 connected to a torque motor 95. The latter and a differential transformer 96 for providing feedback control of a valve 97 which, in turn, controls the motor 72. The movement of the workpiece along the first path is controlled, as in the first embodiment by the sensing element 48, Fig. 9, acting through the spool valve 46 on the hydraulic motors 28<SP>1</SP>. The rotation of the workpiece so that the saw band follows the contour is effected by the changes of illumination on the photo-cells driving the motor 72 to rotate the turrets, the table 63 moving freely along the guideways 66 so that there are no side forces acting on the saw band and the sensing element 48 controlling the valve 46 so that the motors 28<SP>1</SP> maintain a constant force between the saw band and workpiece. In a machine for sawing heavy workpieces in which it is not possible for the plate 63 to move with sufficient freedom along the guideways 66 to maintain the forces acting laterally of the saw blade at substantially zero, a hydraulic motor 102, Fig. 16 is mounted between the primary carriages 60<SP>1</SP> and table 63 and is controlled by an element 103 responsive to deflection of the saw band. In an embodiment using an end mill as the cutting tool, the pressure between the tool and workpiece is sensed by a strain gauge 108, Fig. 15, and controls the motors 28<SP>1</SP> as in the embodiment, Fig. 9, having a band saw.