GB481985A - Improvements in and relating to engraving - Google Patents

Abstract

481,985. Copying by scamning. DALTON, J. W., and BARTHOLOMEW, H. G. Nov. 6, 1936, No. 30320. [Class 40 (iii)] [Also in Group XXII] In a method of an apparatus for producing engraved surfaces in which an image in relief is formed, for instance by etching, in the surface of a plate or like, the plate is mechanically scanned by a device which controls the action on the plate of a cutting tool arranged to increase the effective relief of the image or the prominence of the elevated portions of the plate surface. The plate 1, Fig. 1, is guided at one edge against a guide 3 in an arm 4 adjustably screwed at 7 to a cylinder 5, the other edge being secured to carriage which is moved along a fixed guide arm 8 extending from the cylinder by rack- and-pinion gearing 12 operated from a spindle 30. The cylinder 5 is reciprocated over a tubular piston rod 17 by fluid from a pump 22 driven by a motor 23. Ports 20, 20a allow fluid to flow from tube 17 to one side or other of the piston 18 the reversal being controlled by a valve element 27 having passages 28 and rotated at each end of the stroke through 180‹. For this purpose, at the end of the stroke to the left, the spindle 30 engages an abutment 29 thus causing a toothed ctoment 31 to push back an externally toothed bushing 34 against a spring. The bushing is thus rotated by helical guides 34 until its teeth align with those of the element 31, whereupon the bushing is moved forward by the spring and rotates the spindle 30. This movement actuates the rack-and-pinion gearing 12 to impart cross feed to the work 1 and also acts through gearing 35 to rotate the valve rod 27 and reverse the work movement. A similar action occurs at the other end of the stroke, a toothed element 31a, coacting with a bushing 32a to rotate the valve element to effect reversal and another cross feed of the work. The valve spindle carries a commutator coacting with contacts 38, 39, 40 to energize one or the other of two scanning or work tracing devices 70, 70a, Fig. 2. The contact 40 is connected to an electromagnet coil 44 in circuit with an AC source 45 and one of the scanning devices. A steel disc 47 is rotated from a hydraulic motor 49 and is arranged so that the local magnetization of the disc produced by coil 44 causes after a timed interval, current variations in a coil 50 connected through leads 51 to an amplifying system comprising a valve 52 rectifiers 56 and discharge tube 58. The signal on the disc is obliterated by a third electromagnet 61 connected to an A.C. source 63. Each of the scanning elements comprises a plate 65 with a spherical part 67 which may rock in a recess 68 and a spring pressed ball-ended plunger 70. When the plunger meets a recessed part of the work, it moves forward and engages the contact rings 75 with each other and current flows in the winding 44. After the required delay this causes a current How in the coil 76 of the engraving device, thus moving forward the plunger 77 and forcing the cutter 82 into engagement with the work. The cutter is continuously driven by an air turbine comprising jets 84 and blades 85 on the cutter spindle. The entire cutter assembly is urged towards the plate by a spring 87. In a modification, Fig. 4, the cutting action in correspondence with the etched image on the work is made on the reverse side of the plate. In this case the tool is located opposite the scanning element 89 so that no delay action device is required. When the scanning plunger moves forward into the image, contacts 99 complete the circuit of the coil 76 of the cutter device and cause corresponding in-feed of the cutter 82. In another modification, Fig. 5, for engraving a cylinder 103, the work is scanned by rotating it by worm gearing 108 and moving it axially by a screw 105. A disc 115 driven from the work is provided with a number of pins 116. A scanning device adjacent the engraving element is arranged when it enters a recess in the work to energize an electromagnet 117 to draw forward one or more of the pins to a position wherein they operate a cam ended pin 121 to move the cutter into the work. The pins are subsequently returned by a cam.