Improved grinding fixture for the grinding of spade drills

摘要

1,027,560. Grinding; drills. DE VLIEG MACHINE CO. March 2, 1965, No. 8932/65. Headings B3C and B3D. A fixture for use in the grinding of spade drills 12, Fig. 1, so that surfaces thereon can be ground by a plain surface grinder comprises a tumble block 16 having a plurality of surfaces whereby a drill supported by the block can be positioned at a plurality of different angles relative to a supporting surface 10, the drill being rotatably adjustable relative to the block. The drill 12, Figs. 3 and 12 (not shown), has flat sides 116, 118 and a recessed base 114. The head of the drill has a point 122, cutting edges 124, 126 adjacent primary relief surfaces 128, 130, which in turn are adjacent secondary relief surfaces 132, 134, and chip-curling surfaces 136, 138. Chip-breaking grooves 140 extend across the primary and secondary relief surfaces. The chip-curling surfaces have their centre lines at an angle D to the cutting edges and increase in depth from zero at the centre of the drill to a maximum at the outer diameter. A wedge surface 142, 144 is formed on the side surfaces 116, 118 adjacent the head. The drill is guided in use by circular lands 150, 152 having clearances 146, 148, the lands being ground so as to provide a slight taper longitudinally of the drill. The fixture consists of a seven-sided tumble block 12 which is adapted to be mounted on a magnetic table 10 of a surface grinder having a grinding wheel 19. The drill is mounted on a front surface 22 of the block which is opposite to a pair of rear surfaces 24, 26, Fig. 5 (not shown). The block also has a pair of parallel surfaces 28, 30, a surface 32 perpendicular thereto and a surface 34, and is provided with a stepped bore 36 in which is disposed an insert 56. A workholder 14, Fig. 4 (not shown), having a clamp plate 162 for securing a spade drill thereto, is secured by a bolt 178 to the insert and is angularly located by a dowel 172 engaging a slot 174. The insert is provided with a key 84 which is engageable with one or other of a pair of slots 80, 82 in a ring 78 which is adjustable relative to the block by a vernier scale 98, 100, Fig. 2 (not shown), and is clampable in adjusted position by a ring 88 having screws 96. A nut 64 is rotatable in the bore 36 in the insert but is prevented from axial movement and engages a thread on the insert whereby when the nut is rotated, the insert is axially moved to disengage the key 84 from one of the slots 80, 82 for indexing to the other. Rotation of the nut is effected by rotation of a bevel gear 102, Fig. 4 (not shown) having a socket accessible from a bore 114 in the face 28 of the block, the gear 102 meshing with a bevel gear 112 formed on the nut. In operation and with a drill 12 mounted with its recess 114 engaging the work-holder so that its point is on the axis of the insert 56, the block is placed with its surface 24 on the surface of the magnetic chuck and the work-holder is adjusted to the correct angular position after release of the clamps ring 92 according to the scale 98, 100, the ring then being clamped by the screws to retain the ring 78 in position. With the key 84 engaging one of the notches 80, 82, one of the primary relief surfaces 128, 130 is ground by moving the chuck relative to the wheel. The key 84 is then disengaged from its groove by rotation of the nut and moved to engage the other groove for grinding of the other primary surface. The block is then tumbled so that its other rear surface 26 engages the surface of the chuck and the drill passed across the grinding wheel with the key 84 engaging first one and then the other of the notches 80, 82 for the grinding of the secondary relief surfaces. The chip-breaker grooves 140 are ground by a formed grinding wheel with the face 26 of the block on the chuck surface 10. The chip-curling surfaces 136, 138 are also ground with a formed grinding wheel, the block having its face 30 on the surface of the chuck and a key 184 extending from the face abutting an edge of its surface of the chuck. The relief surfaces 146, 148 on the diameter of the drill are ground with the surface 34 of the block on the chuck, the surface having a slight inclination relative to the axis of the insert to provide the back taper or clearance. Grinding of wedge surfaces 142, 144 is effected with the block held at a predetermined angle by a protractor plate 210, Fig. 20 (not shown), secured to the face 30 of the block. The circular land portions 150, 152 are ground by mounting the drill on an alternative insert 188, Fig. 8 (not shown), which replaces the insert 54 and is not formed with a screw thread but has a key 196 for engaging a keyway 200 formed in the nut whereby the drill can be continuously rotated when the nut is rotated by the bevel gears 102, 112, Fig. 4 (not shown).