Patent GB-668095-A (GB)
Title: Improvements in or relating to grinding machines
IPC: B24B17/04
Filed: 1949-04-26
Abstract: 668,095. Grinding. SHEFFIELD CORPORATION. April 26, 1949 [May 6, 1948], No. 11027/49. Class 60. [Also in Groups XIX, XX and XXIX] A grinding machine including a frame having a work holder and a tool holder, a slide carrying one of said holders for rectilinear feed movement, and a feed screw, comprises interfitting piston and cylinder elements one fixed to said slide and the other manually adjustable by said screw and providing a liquid chamber of variable capacity, means yieldingly urging said piston and cylinder elements towards collapsed condition, an adjustable control chamber having means accessible to the operator for precise control of the size of said control chamber, and a liquid connection between said control chamber and liquid chamber and providing therewith a liquid filled system of constant capacity. As applied to a profile grinder having an optical projection device providing an enlarged surface projection of the work, the grinder comprises a frame 10 having a work-supporting table 11 horizontally adjustable on a vertically adjustable standard 12; the workpiece is clamped on the table by holding screws 13 and a holder clamp 14. A tool holder 15 carries a grinding wheel 16 driven by an electric motor 17 through a belt 18 or other driving mechanism which also causes vertical reciprocating movement of the grinding wheel on the holder 15. The wheel holder 15 is held for rotatable adjustment about a vertical axis on an upper slide 20, an annular groove in the lower side of the wheel holder being engaged by clamps 21 having cam surfaces 23 co-operating with wedge blocks 22 which are internally threaded, one right hand and the other left hand, and drawn together by rotation of a shaft 24 by hand knob 25. The slide 20 is carried by guide bars 26, 27 the ends of which are fixed to depending end flanges 28, 29 on the slide and the middle portions of which are mounted for endwise movement in anti-friction bearing members 30 carried by upwardly projecting walls 31 of a drum 32 adjustable about a vertical axis on a lower slide 33; holding clamps operate on annular groove 32<SP>1</SP>. The slide 33 is movable on a drum 34 in a direction at an angle to the movement of the slide 20; the drum 34 has antifriction bearing members 35 supporting front and rear bars 36 the ends of which are fixed to depending flanges 37 on the slide 33. The drum 34 is rotatable about a vertical axis on a base plate 38 secured to the frame 10; a lock bar 39, operated by lever 40, has an eccentric portion 41 pressing down on a clamp bar 42 carrying bolts the heads of which engage a groove 44 in the drum 34 to secure it in adjusted position. The slide 33 has a passage 46 closed at its outer end by cover plate 47 and the cylinder thus formed contains a piston 48 having at one end an imperforate head 48, the other end being keyed against rotation and being internally threaded to receive a screw 51 rotatably mounted in bearings 52, 53; rotation of the screw 51 by handle 54 applied to the end 55 thereof moves the piston 48 axially and since the space between the parts 47, 49 is filled with liquid, this moves the slide 33. A compression spring 57 interposed between a shoulder 58 on the piston and a shoulder 59 on the slide urges the slide in the direction away from the workpiece so that if leakage from the liquid system occurs the grinding wheel moves away from the work, thus avoiding damage thereto. The chamber 46 is connected by pipe 60 to control means located adjacent the operator's position at the front of the work table; the control comprises a piston 67, operating in a cylinder 68, urged by a spring 69<SP>1</SP> against an adjusting screw 65 rotatable by a knob 61. The diameter of the piston 67 may be much smaller than the diameter of the piston 48 so that a very precise control of the location of the slide 33 is afforded the operator as he adjusts the control knob 61 while viewing the image of the work on the projection screen. The slide 20 is similarly adjusted, coarse adjustment being effected by a handle 54<SP>1</SP> on the end 55' of a screw and fine adjustment by rotation of control knob 61' adjacent knob 61; the two knobs are preferably arranged on the work table 11 which normally does not move during the grinding operation so that they are conveniently accessible. Arranged in the frame 10 is a glass 70 below which is a reflector 71 to project a light beam, coming from a lamp 72, vertically upwards along the edge of the workpiece 73 overhanging the edge of the work table 11. The light that is not interrupted by the grinding wheel or the work is received by an objective lens 74 focused on the work surface. The light is successively reflected by a mirror or prism 75, reflector 76 and mirrors 77, 78, 79 on to the rear side of a viewing screen 80 where it gives an illuminated background 93 and provides a dark shadow image 81 of the grinding wheel. The screen, which may be a ground glass or translucent plate, is provided with lines such as the line 82 that shows a desired contour to be given to the workpiece, line 82 being either a solid line or a dash line; the line may be made directly on the screen or may be on a transparent or translucent sheet of paper fastened to the screen. The several mirrors are carried in a housing 83 of heavy sheet metal fixed to the rear of the machine base 10; the screen 80 is at eye level above the tool and work holders ; a projecting top wall 84 forms a support for a curtain 85 which may be drawn behind the operator's head to cut off the room illumination. The upper surface of the workpiece is also illuminated so that a clear enlarged surface projection of the top of the workpiece is produced on the projection screen. For this purpose, a light source of high intensity arranged in a lamp housing 87 provides, through two parallel tubes 88, two light beams reflected by reflectors 88' and travelling downwardly through two inclined tubes 89 to provide two downwardly converging beams at opposite sides of the line of sight of the objective lens 74. The workpiece, before it is placed on the work table, is scratched in a direction towards the edge to be profiled, so as to be given a series of generally parallel scratches as by rubbing it back and forth with emery cloth. The light beams directed downwardly at an angle to the upper surface of the work and coming in a plane which is transverse of the direction of the scratches on the upper surface of the work produce a bright or light gray detail revealing surface projection 90 of the work, darker than the illuminated background 93 but very much lighter than the shadow image 81 of the grinding wheel. Burns on the work surface are perceptible as a darkening of the work surface at the burned point.