Patent GB-824824-A (GB)
Title: Improvements in or relating to machines for grinding twist-drills
IPC: B24B3/24
Filed: 1957-12-17
Abstract: 824,824. Grinding twist drills. TATAR, A. Dec. 17, 1957 [Dec. 18, 1956], No. 39200/57. Class 60. A machine for grinding twist drills 13, particularly four-faced twist drills, comprises a multi-part support system by which the drill can be supported in various angular positions, a transparent abutment 23 disposed in the working plane 4 of a grinding wheel 3, and an optical device which forms an image of the point of the drill when in contact with the transparent abutment enabling the operator to adjust the support system until the drill can be seen to have a particular angular position about its own axis, whereafter by actuation of the support system, the point of the drill can be moved in the working plane onto the face of the grinding wheel. The grinding wheel is driven by an electric motor in a housing 2 carried on a base 1 and is axially adjustable by means of an adjusting screw 5 to position its working face 4 in the same plane as the transparent abutment in the form of a plate 23. The drill 13 to be ground is held in a chuck 14 adjustably carried on one arm of an L-shaped member 11, the other arm of which is adjustablysecured to a second L-shaped member 9 rotatably adjustable on a drum 7 pivotable about a pin 6 disposed with its axis parallel to the axis of the grinding wheel in lugs 1a on the base 1. The point of the drill when in contact with the plate 23 is illuminated by a light 24, Fig. 5, provided with a truncated conical mirror 25 and its image is formed on a matt screen 29 carrying a reticle 30, Fig. 6, by means of a lens 26, diaphragm 27 and prism 28. Other optical systems using an eyepiece and/or a mirror may be used, the reticle carried on the mirror or plate 23, and the print illuminated by one or more sources of light placed behind the screen. In case, the body of the drill is gripped by the mandrel of the chuck and the lands by the jaws of the chuck which is angularly and axially adjusted on the member 11 until the drill is positioned relative to the reticle as shown in Fig. 6, a locking screw 22 securing the chuck in its adjusted position. The angle at which the point is to be ground can be set by a graduated scale 18 and index mark 17 on the member 9 and drum 7, respectively, means being provided to lock the member and drum together. The cutting and clearance angles of the drill can be set by a graduated scale 19 and index mark 20 on the members 9 and 11, respectively, an adjusting screw 21, when locked in position, permitting the member 11 to move relative to the member 9 between a pair of abutments, the distance apart of which can be adjusted to determine the dihedral angle between the cutting and clearance faces. The support is swung about the pin 6 with the member 11 against one abutment so that the drill moves from the screen to the working face 4 of the grinding wheel to grind, say a cutting face on the drill and, with the member 11 against the other abutment, to grind a clearance face on the drill. The chuck is then rotated 180 degrees to grind the other two faces on the drill. After grinding, the drill point can be brought into contact with the plate 23 for visual inspection with the optical device. Right and left hand drills can be ground by swinging the member 9 through 90 degrees and the member 11 through 180 degrees.