Patent GB-817471-A (GB)
Title: Improvements relating to apparatus for the production of helical thread-like groovesor indentations or the like
Inventor: SAYCE LEONARD ALFRED
IPC: B23G7/00
Filed: 1954-10-14
Abstract: 817,471. Screw-cutting lathes. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Oct. 14, 1955 [Oct. 14, 1954], No. 29642/54. Class 83 (3). [Also in Group XXIII] Apparatus for the production of screw-threadlike grooves or indentations of high accuracy for use in the production of diffraction gratings, comprises a first cylinder 24, Fig. 2, on which the groove is to be produced, a second coaxial cylinder 18 carrying a primary " lathecut " thread, and a bridge-member 42 carrying a tool 58, one end of the bridge-member being attached to a nut which spans a number of lathe-cut threads and engages them by a soft, resilient or elastic material, while the other end extends beyond the first cylinder and is supported by a guide-means 44 which keeps it parallel with the axis of the two cylinders, means being provided also to prevent rotation of the bridge-member. The guide means for the latter comprises a third cylinder 21 coaxial with the other two cylinders. The cylinders are supported by pillars 12, 13 and accurately-aligned bearings set up by a master-bar and secured in the pillars while held in line by a material such as an epoxy-resin introduced into the clearance in liquid or plastic form. The facing ends of the cylinders 18, 21 terminate in centres 22, 23, which form a mounting for female centres in the ends of the polished cylinder 24, on which the accurate thread-groove is to be produced. The cylinders are rotated by a belt-pulley 39, and a fly-wheel 41 is provided on the driving-spindle to give steadiness. The cylinders are axiallylocated against an end-stop 31, hardened steel balls 25, 26, 29 being interposed between the butting ends of the cylinders and drive-shaft. A hand lever 36 and pressure-spring 34 enables the cylinder 24 to be removed from the centres. Tool rests.-The tool 58, Fig. 3, is mounted above the work in a holder 57, which may be raised by a screw 59 and is connected by thin steel strips to a support 55 pivotable about a vertical axis by adjusting-screws 60. The tool, which may be a diamond tool or an abrasive tool, as described in Specification 708,539, [Group XXIV], (see below), is thus lightly poised above the work. A weight 62 is provided at one side of the tool and a weight-pan 63 at the other side to load the tool. A dashpot 66 connected by an arm 65 to the tool-holder is also provided. The tool-holder assembly is supported by a bracket 54 vertically-adjustable on a beam 42, which forms part of a bridge-structure for supporting the tool-holder, nut and guides. A second beam 42, Fig. 2, is arranged opposite the first, and the beams are connected at the drive-end by a nut-holding structure 43, 47, Fig. 4. The elastic pads 45, 46, of the nut are pressed on to the lathe-cut thread of the cylinder 18 by a spring 49, and rotation is prevented by a roller 69 running in a channel 71 secured to the base of the apparatus. The other end of the bridge-member is connected by a cross-piece 44, which has bearing-pads of flexible material resting on the upper half of the guide cylinder 21. When an abrasive tool is used this may be in the form of a six-inch strip of abrasive stone or abrasive-coated paper or other abrasiveimpregnated material. Specification 684,846, [Group XXIV], also is referred to.