Patent GB-993607-A (GB)
Title: Improvements in or relating to twist drills
IPC: B24B3/32
Filed: 1963-12-20
Abstract: 993,607. Drills; grinding twist drills. K. S. MAIER. Dec. 20, 1963, No. 50528/63. Headings B3C and B3D. A method of forming a twist drill comprises continuously rotating a drill blank, bringing the blank and a grinding wheel into contact to form a cutting lip and a main land on the blank, separating the blank and grinding wheel for a predetermined degree of rotation of the blank, bringing the blank and grinding wheel into further contact, thereby to grind a further surface on the blank, bringing the blank and grinding wheel closer together to form an undercut centering lip, and separating the blank and grinding wheel, the method being repeated once during each revolution of the blank for each cutting lip required. Drills.-The drill is shown in Fig. 2 and has cutting lips 12, followed by lands 10, which are backed off at 15, and centering lips 14, which are undercut to provide a positive cutting angle. A device for grinding the drill is shown in Figs. 5, 10, and comprises a base plate 20 which carries a grinder frame 22, pivotable about an axis 22a, and a main housing frame 21 which is inclined to the vertical. An arm 25 pivots in the directions X 1 -X 2  about a shaft 24, and supports a slide 27 for movement in the direction Y 1 -Y 2 , guided by a rail 26. Arm 25 is urged by a torsion spring 46 which is adjustable by a worm and wheel 48, 49. A drill chuck housing 28 pivots on slide 27 about a shaft 29 in the directions Z 1 -Z 2 , and rotatably carries the drill 30 to be ground. Arm 25 is pivoted by a cam 31, which rotates about shaft 29 at twice the speed of drill 30. A pair of cam followers 32 carried by slide 27, cooperate with a fixed guide 21b and cam 31, so that as the latter rotates, the assembly 26, 27, 28 pivots about the shaft 24. Slide 27 carries a roller 33 which co-operates with a cam plate 34 to provide movement in direction Y 1 ,Y 2 , the cam plate and roller being urged into engagement by springs 35. A second cam 37 is fixed to cam 31 and co-operates with a roller 40 carried by a lever 38 pivoted on slide 27 at 38a. An adjustable stop 39 is provided for the lever, and the latter rests against a stop 41a on housing 28. Upon rotation of cam 37, lever 38 is pivoted to move housing 28 in the direction Z 1 , Z 2 . In operation, cam 31 contacts roller 32 at point A, Fig. 8, arm and slider 27 are swung out to the extreme left hand position as seen in Fig. 5. Grinding wheel 23, Fig. 9, is beginning to apply edge 51 to cutting lip 12, and in this position roller 33 rests against part 34a of cam plate 34, whereby slide 27 is fully retracted. Lever 38 with its roller 40 is clear of cam 37 adjacent point A 1  and housing 28 is firmly coupled to the slide. Cam 31 is rotated in direction Z 1  and roller 32 travels along the cam in direction a, thus pivoting arm 25, slider 27, and housing 28 in direction X 2 . Roller 33 also travels along part 34a of cam 34 and slide 27 advances slightly in direction Y 1 , while the grinding wheel cuts the land 10 as the drill rotates. The edge S 2  of the grinding wheel, Fig. 9, has now reached the back edge of the land at 10a, cam 31 and roller 32 are at point B in Fig. 8, and roller 33 is at point 36 on cam 34. Cam 31 continues to rotate, and roller 32 follows a cylindrical part B-C of the cam, and no pivoting of arm 25 takes place. However, when roller 32 reaches point B on cam 31, roller 40 reaches point B 1  on cam 37. Roller 40 is lifted, and pivots lever 38 and housing 28 in direction Z 1  about shaft 29, thus moving drill point 30a away from the grinding wheel 23. At the end of this operation roller 32 has reached point C and roller 40 has reached point C 1 . In the next part of the cycle, roller 40 reaches non-lifting part C 1 -D 1  of cam 37, and housing 28 pivots back to bring the drill point into contact with the edge S 2 of the grinding wheel at point K, Fig. 9. Roller 32 travels from C to D and roller 33 moves along part 34b of cam 34, allowing the slide to advance in direction Y 1  to grind surface 15, Fig. 9, and to undercut centering lip 14. When roller 32 reaches point D, Fig. 8, surface 15 on the drill is complete and lip has been provided with a positive cutting angle. Roller 40 has now reached point D 1 , and the drill is disengaged from the grinding wheel. Rotation of cam 31 is continued, and roller 32 follows curve D to E ready for grinding the second lip 12, and this is also the position for changing the drill. An electric motor 42, Fig. 10, drives shaft 24 and the latter is connected to shaft 29 by a shaft 56, Fig. 14. A worm 57 is fixed on shaft 24 and engages with a worm wheel 58 mounted on shaft 56. Shaft 56 can slide in wheel 58, and in arm 25, and passes through a bore in slide 27. Axial movement of shaft 56 is limited by a sleeve 62 fixed to the shaft, and by a claw coupling 63, which engages with a claw 64 to drive shaft 65 in slide 27. A worm 72 mounted on shaft 56, 61 engages with a wormwheel 73 on shaft 29, and the latter has a bevel wheel 74, Fig. 10, which co-operates with a bevel wheel 75 of twice the diameter for rotating drill 30 at half the speed of that of cam 31. Shaft 65, Figs. 14, 15, is axially movable and has an annular groove 81 which carries roller 82. The roller is carried by a lever 85 mounted in slide 27 and engages a push rod 86, which slides in the slide 27 parallel to shaft 65. A lock actuated bolt 89 cooperates with the rod and is adapted to enter an opening 91 of a plate 92 fixed to housing 28, and also to actuate a toothed plunger 94 so that it engages a toothed wheel 100 on the drill chuck 76, Fig. 10, to stop rotation of the drill. Housing 28 has a tubular extension 101, Fig. 18, in which a knurled sleeve 102 is slidably mounted. A spring 103 is disposed between a guide extension 104 in housing 28 and a plug 105, and a stop 106, Figs. 19, 20, on sleeve 102 enters a bayonet slot 107 in extension 101; when the spring is compressed, and engages a stop 108. Another stop 110 on housing 28, Fig. 18, contacts a stop 11 on the slide or arm 25. An extension of slide 27 carries a stop strap 112, Fig. 13, pivoted at 112b for positioning drill point 30a. Cam plate 34, Fig. 10, is adjustably mounted on a lever 113, which is pivotally mounted on frame 21, and a scale is provided for indicating the position of the lever, and therefore the relief angle of land 10. Lever 113 is mounted on a carriage 119 which is adjustable by a spindle 119a. In a modification, Figs. 21, 22, both the drive unit 120 and a grinder unit 122 are vertically mounted on base plate 20, and unit 122 is pivotable about axis 22a and is set by bolts 121a-121c, two of which are located in a part circular track 123, thus allowing swinging of the unit in direction q 1 -q 2  about axis 22a. Grinding wheel 23 can be advanced in direction I by a handwheel 125, and a diamond 128 can be pivoted down about shaft 129 to engage a stop and dress the wheel.