Patent GB-475986-A (GB)
Title: Improvements in collapsible screw threading taps for pipe couplings
IPC: B23G1/22
Filed: 1936-10-28
Abstract: 475,986. Taps. FAIRWEATHER, H. G. C. (National Acme Co.) Oct. 28, 1936, No. 29375. [Class 83 (iii)] A collapsable taperthreading tap has circular chasers mounted for radial movement on the body and an adjustable member slidable on the body for engaging the end of the work to cause a wedge core to remain stationary during the axial travel of the body for producing the taper thread. The body 1 has radial undercut grooves 5, Fig. 1, to receive carriers 6 for circular chasers 15. - Springs 9, Fig. 5, located in pockets in the body engage lateral pins 7 on the carriers to maintain axial surfaces 11 thereon in contact with wedge and cam surfaces 28 on a central core 2. Movement of the carriers along the wedge surfaces causes a taper thread to be cut, and rotation of the core adjusts the diameter of cut through the cam formation of the surfaces, as shown in Fig. 5. The core 2 is connected by a transverse pin 39, Fig. 1, passing through axial slots 40 in the body 1, to a ring 42 axially slidable on the body and also capable of slight rotation to adjust the diameter. This rotation is caused by tangential screws 45, Figs.1 and 3, engaging pins 50 projecting axially from the ring 42 through arcuate slots in a ring 35 which is slidably keyed to the body by keys 48, Fig. 3. A ball thrust race 52, Fig. 1, is placed between the ring 42 and an adjustable work-stop 43, axial motion between the stop and ring 42 being prevented by a yoke ring 51. In operation, with the core 2 fully advanced from the position shown in Fig. 1, the stop 43 engages the end of the work C and remains stationary at the same time as the chasers 15 commence to cut, thereby preventing further advance of the rings 42, 35 and the core 2. As the carriers 6 move along the core they recede and cut a tapered thread and when the desired length of thread has been cut, bevelled portions 13 on the carriers ride over the bevelled end 44 of the core and allow the tap to collapse. The core is exchangeable to provide different degrees of taper and different lengths of thread, Sliding movement is imparted to the ring 35. in order to reset the core 2 after a tapping operation, by means of a ring 30 rotatable by a radial handle 31. and carrying radial rollers 36 engaging helical cam grooves 37 in the body 1, the rings 30, 35 being connected by screws 33, Fig. 3, and arcuate slots 32 to allow rotation of the ring 30. When the tap is used in a vertical position, the weight of the core and rings &c. is partly balanced by a spring 52". The chasers 15 have annular grooves 14 without lead, and are inclined to the axis of the tap at the thread angle by making the forward face 6<1> of each carrier inclined. The outer periphery of each chaser is conical, as shown in Fig. 1, so that the first grooves cut the thread whilst the final grooves act as a guide and all the chasers are identical except in height, which is reduced from one chaser to the next by a portion of the pitch of the thread depending on the number of chasers in the tap. Each chaser is located on its carrier by a cylindrical pilot 19, Fig. 7, and is adjusted angularly about the axis of the pilot, after grinding, by means of a bushing 22 having serrated portions 21, 24 engaging respectively with serrations on the carrier and chaser. The serrations 21, 24 are of different pitch so that a differential adjustment may be effected, and the chasers are secured by central screws 26. Each chaser has a segmental portion 15<1>, Fig. 5, removed to form a cutting edge 16 which is intersected by an end recess 27<1> serving for chip clearance. Shanks.-The tap is floatingly supported by means of flanges 53, 54, Fig. 1, and an intermediate plate 55, the assembly being loosely held together by three screws 56 and the plate being connected to the flanges by pairs of rollers on pins attached to the flanges engaging radial opposed slots in the plate.