GB1484016A - Manufacture of screw-thread forming dies - Google Patents

Abstract

1484016 Grinding; rolling; making screw threads ALFRED HERBERT Ltd 15 Nov 1974 [17 Nov 1973] 53473/73 Headings B3D B3A and B3M A method of making a thread-forming die comprises the steps of making a rotary forming tool by forming on a cylindrical surface of a tool blank first and second groups of alternating parallel ridges and grooves of the same pitch by applying forming means to the blank, the forming means being applied in such a manner as to form between the first and second groups a further ridge or groove 9, Fig. 5, of a different pitch, and using the tool so formed to form a thread-forming die 10, Fig. 6, or an intermediate for forming the die. In order to produce the forming means, which is in the form of a crusher roller, a first grinding wheel, Fig. 1, is conventionally diamond dressed to have ridges 1 and grooves 2 of a pitch Pc which has a correction to accommodate, in the forming of a screw, the helix angle for a screw having a pitch P. The ends of the wheel have half grooves 3. The first grinding wheel 4, Fig. 3, is fed into the crusher roller to form a first group of ridges 5 and a half-ridge 6. The grinding wheel is then moved axially a distance equal to the number of ridges multiplied by the pitch Pc plus a distance X and then forms a second group of ridges with one ridge 7 of greater or lesser pitch. The ridge 7 is treated to remove a protruding portion and so as to form, as shown in Fig. 5, a broad ridge 9. The crusher thus formed is used to form a second grinding wheel which, in turn, is used to produce the die 10, Fig. 6, having a broadened ridge 9 between ridges and grooves of normal pitch. The crusher roller may, alternatively, be produced by a turning or electrolytic grinding, or a hob may be ground and used to cut the die directly. A pair of dies so produced is used to produce a screw thread having a portion of different pitch between portions of the same pitch for locking engagement with a nut, one of the dies being fixed and the other relatively movable in the longitudinal direction of the dies to form the screw thread on a blank fed between the dies.