GB605279A - Improvements in or relating to method and apparatus for the cutting of metal dies for casting optical selector nets - Google Patents

Abstract

605,279. Shaping curved surfaces. RELIEPHOGRAPHIE SOC. POUR L'EXPLOITATION DES PROCEDES DE PHOTOGRAPHIE EN RELIEF M. BONNET. Nov. 8, 1945, No. 29863. Convention date, Dec. 1, 1944. [Class 83 (iii)] The surface of a cylinder is engraved by a cutting tool oscillating about an axis disposed at right angles to a plane containing the axis of the cylinder and passing through the longitudinal axis of the tool, the tool being dis. engaged from the work after each operative stroke. The tool 21, Fig. 8, is mounted in a holder 20 adjustable on an arm 19 fixed to a shaft 18 eccentrically mounted in a sleeve 8. The shaft 18 has a lever 17 oscillated by a rod 16 connected to cranks 15 on a shaft 14 rotated by a main shaft 24 through bevel gears 22, 23. To lift the tool from the work during the return stroke, a cam 13 on the shaft 14 acts on a spring-loaded lever 9 and rotates the sleeve 8. The cam and the roller 12 on the lever separate during the cutting stroke so that the depth of cut can be adjusted by an abutment 11. The work-piece 6 is wrapped round a holder 5 on a shaft 2, having a ratchet wheel 29 and a lead screw 3 engaging a nut 4 and is rotated and fed axially after each cutting stroke by a pawl bar 28. The pawl bar is carried on arms mounted on eccentrics 25 on the main shaft 24 and is counterbalanced by a weight 33 on arms mounted on eccentrics 30 oppositely disposed to the eccentrics 25. For cutting grooves of elliptical or similar cross-section, a pantograph, Fig. 9, is fitted between the levers 17 and 9 and has an adjustable roller 39 engaging a patter 40, which corresponds in function to the abutment 11 in Fig. 8. Fig. 4 illustrates the cutting action of the tool across the groove while oscillating about the axis XY and shows a tool, which may be diamond-tipped, having a straight cutting edge C and a rear face D having angles α and # which are as large as possible within the limits necessary to prevent the rear face touching the work at the end of the cutting stroke. For cutting cells of part-spherical cross-section in the workpiece, the tool may have a circular cutting edge of radius equal to the distance of the tip from the axis XY of oscillation and by adjusting the tool round a vertical axis in the holder 20, the cutting edge can be placed obliquely to the work and cells of smaller radii than the edge of the tool can be cut. The setting of the tool may be facilitated by projecting the silhouette of the cutting edge and the bottom of the groove on a screen. The apparatus is particularly applicable to the engraving of moulds for casting lenticular optical selector nets; any scratches due to imperfections in the tool lie across the part-cylindrical lens instead of along it.