Patent GB-448922-A (GB)
Title: Improvements in screw threading taps
IPC: B23G1/22
Filed: 1935-09-16
Abstract: 448,922. Taps. FAIRWEATHER, H. G. C., 65, Chancery Lane, London.- (National Acme Co. ; 131st Street, Cleveland, Ohio, U.S.A.) Sept. 16, 1935, No. 25615. [Class 83 (iii)] In a collapsable taperthreading tap, chasers are carried in radial slides in a body and are positively connected to a taper core which is movable relatively to the body during threading by means of a lever pivoted to an outer sleeve which abuts against the end of the work and having an adjustable pivotal connection with the core. The body 2 has radial guides 9 for carriers 8 to which circular chasers 10 are attached by screws 22, and which have hooked ends 6 engaging undercut recesses 5 on the tapered head 4 attached to the core 3. The lever 26, which passes freely through a slot in the core, has a recess 40 at the upper end receiving a head 39 on a pin 39a freely rotatable in a block 34 which is adjustably secured in a recess in the outer sleeve 1 by means of screws 36 and slots 38. The lower end of the lever 26 is freely slidable in a disc 25 which is freely rotatable in a yoke 24 secured to an inner sleeve 1<1> slidable on the body 2. Two bars 30, one on each side of the lever 26, are rigidly attached to recesses in the core 3 by means of straps 31 and are provided with two holes 27A, 27B corresponding in position with similar holes in the lever 26. A pin 28 may be inserted through either set of holes to connect the lever with the core. In operation, the tap is fed towards the work and when an exchangeable ring 41 on the sleeve 1 engages the work x further motion of the sleeve is prevented. The chasers continue to feed forward the body 2, the sleeve 1<1> and the yoke 24 and disc 25, the sleeve 1<1> abutting through an adjusting ring 53 thereon against a stop 44, Fig. 6, on the body 2. This motion swings the lever 26 about the stationary pin 39, the pin 28 moving slightly more slowly than the disc 25 due to its being nearer to the pin 39, and hence the core 3 connected to the pin 28 will move more slowly than the body 2, causing the carriers 8 to travel along the head 4 and withdraw the chasers gradually to cut a tapered thread. By transferring the pin 28 from the holes 27B to the holes 27A, which are midway between the holes 27B and the centre C of the disc 25, the degree of taper may be halved. A fine adjustment of the taper is obtained by adjusting the block 34 radially, by means of the slots 38, in order to vary the distance of the pin 39 from the disc 25 and pin 28. The core 3, sleeve 1<1> and yoke 24 are normally drawn in a rearward direction, with the ring 53 abutting the stop 44, by means of a spring 54 attached to the core and body 2, and adjustment of the diameter of the tap is effected by screwing the ring 53 axially on the sleeve 1<1> and locking by a nut 57. The ring 41 and tapered head 4 may be changed for others in order to operate on work of widely different diameter or to accommodate different numbers of chasers, and the head is located by a spigot and socket 12 and is secured by a screw 11 and pins 12a. For collapsing the tap after completion of a threading operation, a dog 42, Fig. 6, is adjustable along a slot 43<1> in the sleeve 1 and remains stationary whilst the ring 41 is against the end of the work. As the body 2 and sleeve 1<1> move forwards, a stop 49 attached to a slide 47 within the body is carried against the dog whereby the slide is moved rearwardly in the sleeve and its bevelled end 52 acts on a roller 45 on the stop 44 to depress the stop against springs out of the path of the ring 53 and thus allow the spring 54 to draw the core 3, sleeve 1<1> and yoke 24 rearwards relatively to the body 2, thereby collapsing the tap. To re-set the tap a yoke &c. on the machine may engage a ring 58 on the sleeve 1 as the tap is retracted, thereby drawing forward the sleeve 1<1> through stops thereon (not shown), until the stop 44 snaps out to lock behind the ring 53. Alternatively a hand lever may be inserted through slots in the sleeves 1, 1<1> to engage a pin on the body 2, whereupon oscillation of the lever in an axial plane will move the sleeve 1<1> forwards. The circular chasers 10, which are shaped to correspond with the taper of the work, as shown in Fig. 1, have circular thread grooves 10<11> without lead and the faces 8<1>, Fig. 16, of the carriers 8 are inclined to give the grooves the correct helical angle and clearance for the thread being cut. All the chasers in the tap are identical except that the rear faces 10a are spaced from the first groove according to the position around the tap so as to position the successive chasers along a helix. Each chaser is secured to its carrier 8 by a left-hand screw 22 and is angularly adjusted to position the radial cutting edge 10<1> after grinding by means of a pilot bush 18 entering recesses in the chaser and carrier. Serrations 19, 20 of different pitches on the bush 18 engage similar serrations in the carrier and chaser respectively in order to provide accurate angular adjustment, the front face of the bush being graduated to facilitate the adjustment The outer periphery of the boss 14 on the carrier is an accurate fit in the serrated recess of the chaser. For cutting left-hand threads carriers 8 having faces 8<1> of opposite inclination are used. The tap may be rotary or non-rotary.