1408171 Grinding cutters; work-holders; cutters F A B VALENTINE 24 Aug 1972 39518/72 Headings B3D B3B and B3K A machine for grinding an end mill of the type having a fluted shank at the end of which is a plurality of cutting edges symmetrically disposed about the axis of the shank and radially thereof, and each edge having a face area at th back thereof formed with axial clearance relative to a plane normal to the axis, comprises a grinding wheel 31 rotatably mounted on a frame F, a workhead H including a collet 48 for clamping the end mill, carriage means 120 mounting the workhead on the frame for feed movement towards a position of engagement of the end mill with the grinding wheel, means pivotally mounting the workhead on the carriage for movement about a swing axis 32 perpendicular to the longitudinal axis of the end mill to bring different portions of a cutting edge to bear against the grinding wheel, and co-ordinating means for motivating the feed and swing movements to occur in a predetermined sequence In one sequence, the end mill B, Fig. 6A, is loaded in the machine with its axis 58 parallel to and spaced from a plane 47 containing the axis of the grinding wheel and the swing axis 32. The end mill is fed into the grinding wheel, swung about the axis 32 to form an arcuate cutting edge, retracted from the wheel, swung back to its initial position and then indexed for grinding the next cutting edge. In another sequence, the end mill 20, initially positioned with its axis inclined at a primary angle #, Fig. 6G, to the plane 47 and then swung about axis 32 to a secondary angle #, Fig. 6H. The end mill is then fed to the grinding wheel to grind the cutting edge to the secondary angle, retracted, swung back to the initial angle, fed into the wheel for grinding the primal y angle, retracted, and then indexed for grinding the next cutting edge. The first sequence provides an end mill having a cutting edge as shown in Fig. 4, and the second sequence a cutting edge as shown in Fig. 5. The grinding wheel 31, Fig. 8, is mounted in a vertical spindle 35 rotated by a belt drive 37 from a motor 36. The workhead H is mounted in a carriage in the form of a yoke 120 and has upper and lower trunnions 45, 46, Figs. 8 and 10, defining the swing axis 32 which, with the axis 35 of the grinding wheel, define the plane 47. The workhead has a pair of spaced bearings 53, 54 between which is a collet 55, and the end mill is held in a tool holder 48 which is removably received within the bearings and collet. The tool holder, Fig. 19, has an internal sleeve 49 which is urged by a spring 49A to cause a collet 50 to grip the end mill, handles 51 being provided to act against the spring to release the collet 50. The collet 55 is moved to grip the tool holder 48 by fluid pressure acting on a piston 56, the piston moving against a spring 56.3 which urges the collet to the open position. The workhead is divided into front and rear halves H 1 , H 2 , the part H 1 being rotatable relative to the part H 2 to vary the distance of the axis 58 of the end mill and tool holder 48 from the plane 47 defined by the axis 35 of the grinding wheel and the swing axis 32 of the workhead H, the halves being releasably secured together by a clamping ring 61 which can be tightened by a screw 41a. The distance between the axis 58 and plane 47 is shown by a pivoted arm 64, Fig. 12, reacting over a scale 63. The forward face of the rear half H 2 of the workhead is measured and rotatably receives an internally-toothed ring gear 66 which engages a gear 67 formed on the bearing sleeve 54 for receiving the tool holder for rotational indexing thereof, a gear 68 on a shaft 70 driven by gearing from an hydraulic motor 75, and a gear 78 on a shaft 81 connected by bevel gearing 82, 83, Fig. 16, to a flute selector mechanism. The gear 83 is mounted on a shaft 84 on which is secured a first disc 87 and extends to a knob 85. A second disc 88 is rotatably mounted on the shaft and connected to a knob 90. Disc 87 has a join 91 engageable with a selected one of three holes 91, 93 in disc 88 so that notches on the edges of the discs can be aligned to form two, three or four gaps in the periphery of the discs corresponding to the number of flutes on the end mill. A pin 96 on a linkage is connected to valves of a pneumatichydraulic circuit controlling the operation of the machine. One of the gaps is deeper than the others so that movement of the pin into that gap initiates the last cutting edge to be ground. Accurate angular locations of the toolholder following an indexing movement is effected by engagement of a locking pin 107, Fig. 10, movable by an hydraulic motor 108 into a selected one of a number of holes 53a in the periphery of the chuck sleeve 53. The hydraulic motor 75 supplies a reduced pressure to act on the indexing mechanism so that pin 107 bears against a side of the selected hole 53a to eliminate backlash. The carriage 120 is in the form of a yoke having arms 45a, 46a, Fig. 9, for the upper and lower trunnions 45, 46 of the workhead. Arm 46a is mounted mid-way along its length on the upper end of a vertical inner sleeve 121 oscillatable and vertically movable in an outer sleeve 122. A shaft 126 is disposed within sleeve 121, the lower end of which co-operates with a yoke 130 movable about an adjustable pivot 131 by an hydraulic cylinder to move the workhead between a grinding position and a loading position in which the end mill is positioned by engagement with a locator 110, Fig. 10. A collar 140, Fig. 18, is secured to the lower end of the sleeve and has one arm 140a connected to a spring 142 and a second arm 140b engaged by a roller 143 movable by an arm 144 rockable about a pivot 145 by an eccentric 150 rotated by a linkage connected to an hydraulic cylinder 157 the oscillation of the sleeve by activation of the cylinder 157 rocks the workhead about the axis of the sleeve so that the end mill carried by the workhead is fed towards and away from the grinding wheel. The upper end of the shaft 126 is connected by a parallel linkage 166, 167, 168, Fig. 15, to the journal 46 of the workhead, the rocking of the linkage being limited by adjustable stops 176, 177 and being effected by an hydraulic cylinder 160, Fig. 18, connected to the lower end of rod 126 by a link 162 and arm 163 secured to the rod. The operation of the machine is automatically controlled so that the sequence of operations produces an end mill having arcuate cutting edges, Fig. 4, or cutting edges ground at primary and secondary cutting edges, Fig. 5, at its end, the various hydraulic cylinders and operations being controlled by a pneumatic logic circuit.