Patent GB-676162-A (GB)
Title: Improvements in or relating to a threading machine and method of making an interrupted thread tap
IPC: B24B3/18
Filed: 1950-06-19
Abstract: 676,162. Milling screw-threads making screw-taps. SHEFFIELD CORPORATION. June 19, 1950 [June 28, 1949], No. 15251/50. Classes 83 (ii) and 83 (iii). [Also in Group XXIII] A machine for making helically - interrupted threads, comprises a base 10, Fig. 1, means for mounting the workpiece, a grinding wheel or cutter 18, Fig. 4, having a thread - forming groove and a generally cylindrical portion extending axially to each side of the groove for a distance sufficient to accommodate a further thread - forming groove, means for supporting the tool 18 for transverse movement relatively to the axis of the work and for periodically temporarily removing it from the work for predetermined parts of a revolution of the work, and means for rotating the work and for moving it and the tool 18 relatively in a direction axially of the work. A tap blank 4 having an odd number of lands a, b, c is mounted between headstock and tailstock centres 12, 13 supported on a table 11 traversable along the base 10 through a lead screw, (not shown), driven by a motor 16 also arranged to rotate the headstock face-plate 15. The headstock drive is coupled through gears 50, 51, Fig. 2, to a mechanism connected by a screw 22 to a slide 19 carrying the grinding wheel so that the latter is caused to jump alternate lands during rotation of the blank. The screw 22 is fixed to a sleeve 23 which bears within a further sleeve 24. A cam surface 35 on the end of the sleeve 24 co-operates with a cam-sleeve 34 having a handle 28 so that upon rotation of the handle it is caused to move axially away from the sleeve 24 and displace the screw 22 through engagement with a flange 25 on the sleeve 23. This rotation of the handle 28 produces rapid advance of the grinding wheel to the work against a weighted cable or chain. Fine adjustment of the grinding wheel is effected by rotating the screw 22 through a wheel 30 connected by springs 32 to the flange 25. A lever 38 is rocked about a pivot 39 on a slide 57 which is supported between ways 58 on the base 10 to produce automatic oscillation of the grinding wheel and, if desired, thread relief. A bifurcated end of the lever 38 is received in recess 36 in the sleeve 24 to engage the sides thereof and react against the weighted slide 19. The other end of the lever 38 engages the wall of a recess in a slide-block 42 which is oscillated in a housing 43 by a cam 41 in engagement with the slide-block and rotated through a shaft 49 carrying the gear 50. The automatic oscillating mechanism may be disengaged by a lever 52 which can be turned to move the slide-block 42 into a position beyond the reach of the cam 41. Taper-threads may be cut by traversing the pivot 39 by means of a cam 55 on the slide 57 which is displaced by a pin 60 carried along in engagement with the cam 55 and a part 61 of the base 10 by a part 62 of the table 11. The cam 55 may be rendered inoperative by drawing the slide 57 away from the pin 60 and clamping a block 64, normally secured to the base by a screw 65, between a post 63 on the slide and the front wall of the base by means of a screw 65a. The grinding wheel 18, Fig. 4, which is driven by a motor 20, has preferably a number of thread grooves therein separated by generally cylindrical surfaces of width equal to that of the grooves so that upon grinding alternate lands in a blank having an odd number of lands, a thread may be formed after two complete rotations of the blank which is interrupted helically on alternate lands. Tap blanks may be used which have previously been formed with a rough thread.