Patent GB-694990-A (GB)
Title: Improvements in ruling engines for the manufacture of diffraction gratings
IPC: B44B3/02
Filed: 1951-05-08
Abstract: 694,990. Engraving. STRONG, J. D. May 8, 1951 [May 31, 1950], No. 10794/51. Class 100(ii) [Also in Group XXV] Apparatus for the ruling of diffraction gratings is provided with a reciprocating carriage adapted to support a plane or curved surfaced blank to be ruled while the ruling tool is supported by and between two nuts each engaging its respective one of two lead screws journaled for rotation about parallel axes transverse to the direction of motion of the carriage, the screws being rotated after each reciprocation of the carriage through constant increments of angle so as progressively to move the tool transversely of the carriage path. As shown, a carriage 12, Fig. 1, supporting the blank 40 e.g. of glass covered with an extremely thin layer of aluminium, to be ruled with, e.g. 15,000 lines per inch, is reciprocated under the ruling tool 37 by a link 20 connected to a source of power. The ruling tool is operative during one stroke of movement of the carriage and is lifted clear of the blank by mechanism 8 during the return stroke. The carriage 12 is guided on two coaxial cylindrical ways 14 whose axes-lie substantially in the plane of the axes of the lead screws 22 for progressively moving the tool 37 under control of the dividing heads 28. Substantially the whole weight of the carriage is borne by shoes 19 adapted to glide on auxiliary ways 18 disposed on each side of the carriage and whose bearing surfaces also lie substantially in the plane of the axes of lead screws 22. Universal joints (see Group XXV) comprising sleeve bearings 61, Fig. 2, couple the carriage 12 to each of the ways 14, each sleeve being tapered and having e.g. an average clearance of .0005 inch and fitting over the cylindrical ways 14 with a graduated clearance, e.g. of .0001 inch per inch of length, being greatest at the end of the bearing which leads during the working stroke of the carriage. A ball bearing member 63, Fig. 2 e.g. of glass, is fixed to the sleeve 61, and has a working surface conforming to a zone of a sphere coaxial with the sleeve. A socket bearing member 67 is affixed to the carriage and its working surface matches the working surface of ball member 63, the two members being stressed together by resilient means such as cantilever springs 71. The ruling tool 37 is carried by a connector bar 36, Fig. 2, supported by nuts 32 engaging the lead screws 22, the bar 36 being pivotally linked to each nut 32 as regards motion in planes parallel to the axial plane of the screws and the lines of centres of the pivots being inclined to the perpendicular to the axes of the screws at the pitch angle of the screws. Each nut 32 has two contact pads 102, 104, Fig. 5, at the top of a frame 35 constituting the nut to take the weight of the connector bar 36. The driving connections between nuts 32 and bar 36 determine the position of the bar and hence of the tool 37 in horizontal planes parallel to the axial plane of screws 22 and comprise studs 110, Fig. 5, one on each nut 32 extending above the pads 102, 104 to pass through apertures 111 in the bar and to bear against bearing elements 112 in the walls of the apertures. The bearing surfaces of elements 112 are oriented parallel to the long dimension of the bar 36 and the nuts 32 are located with respect to each other on the screws 22 so that the line of centres of the driver bearings 110, 112 is inclined to the axes of screws 22 at an angle differing from a right angle by the pitch angle of the screws. The frames 35 are adapted to fit with clearance over the upper half of the screws 22, as shown in Fig. 2, and have each four threaded pads 30, 31, 33, 34, Fig. 5, affixed thereto in position to engage the thread of the screws over areas of the screws lying adjacent opposite ends of a screw diameter within arcs of circumference of the screw separated by an arc of not less than 180 degrees on the side of the screw opposite the frame 35. Each frame 35 has a wing 46, Figs. 2 and 5, provided with a contact pad 106 which is retained against the bar 36 by a spring clip 107 so that during the ruling step the bar is clamped while during the pawling of the screws counterclockwise to advance the bar the contact between the frames 35 and the screws 22 is loosened. The shafts of screws 22 protrude beyond the bearings 21, 23, Fig. 1, and counter-weights 24 are provided to minimize the sag of the screws between the bearings. The blank 40, Fig. 2, is conveniently supported on a tripod 41 and steel plate 43 so as to lie in or near the axial plane of screws 22.