GB432666A - Improvements in and relating to method of and machine for hobbing threading tools - Google Patents

Abstract

432,666. Making screw-cutting taps or dies. TRIGGS, W. W., 57, Lincoln's Inn Fields, London.-(Greenfield Tap & Die Corporation ; Sanderson Street, Greenfield, Massachusetts, U.S.A.) Oct. 12, 1934, No. 29247. [Class 83 (iii)] In a method of making a thread-cutting tap or die having a number of circumferential lands separated by longitudinal flutes the teeth along a land 1 are first cut so that they lie to one side of a normal helix line P to provide clearance on the side a<1> of the teeth and the teeth of the next land 2 are then cut so that they lie on the opposite side of said helix line, to provide clearance on the opposite side b<1>. The teeth of the lands 3 and 4 of a four-flute tap are in helical alignment with those of the lands 1, 2 respectively, clearance being thus provided at c<1> and d<1>. For making a tap T the work is mounted on a spindle 10 and all the teeth of a land are cut simultaneously by a hob H having parallel rings of teeth and moved axially by a cam 33 to the required pitch, the cam being driven by gearing 36. The hob is driven from a flexible shaft 25. In order to produce the alternate off-setting of the teeth the cam groove has stepped portions as shown in Fig. 2, the portions a, b, c and d being operative to produce the teeth on lands 1 .. 4 respectively, and the cam rotating at the same speed as the work. The amount of offset may be about À003". In the application to the three-land tap the axial shift between the first and second lands may be half of that between the second and third lands.