Patent GB-622440-A (GB)
Title: Device for cutting screw-threads in tapered holes
IPC: B23G5/14
Filed: 1947-03-25
Abstract: 622,440. Taps. NICOLAI, A. F. A. March 25, 1947, No. 8166. [Class 83 (iii)] A taper-threading tap comprises chasers 1 slidable in a rotary head 2 by means of a wedge core provided on an axially-movable feed-bar 3, an outer sleeve 4 attached to the head 2 and gripped by a driving chuck, an actuating piston 6 coupled to the feed bar 3 and axially movable in an inner sleeve 5, one end of which penetrates a hollow piston 7 slidable in the outer sleeve 4, the piston 6 being slotted at 8 and 9, the inner sleeve 5 at 10 and 11, and the piston 7 being formed with a slot 12, bridged by a pin 13, and a slot 14, a coupling pin 15 penetrating the slots 9, 10, and 14, a compression spring 23 which urges the piston 7 away from the head 2, a detent 16 mounted on the outer sleeve 4 and engaging the pin 13, the detent being moved out of engagement with the pin 13 by the engagement of a bar 22 with a lever 17, a hook 19 then engaging the face of the piston adjacent the spring 23, an actuating sleeve 20 to which is fastened a pin 21 extending through a slot in the outer sleeve 4, through the slot 11 in the inner sleeve 5, and through the slot 8 in the piston 6, and a linkage 26, 28, 30 so connecting the end of the spring 23 to the pin 21 that the latter, and hence the sleeve 20, is urged towards the head 2. In operation, the tap is entered in the hole to be screw-threaded and as the thread is being cut, the sleeve 20 is moved axially away from the chasers 1 and the pin 21 traverses the slot in the outer sleeve and the slot 8 in the piston 6, and carries the inner sleeve 5 along with it. The pin 15 is forced to traverse the slot 14 in the piston 7 and as the latter is restrained from axial movement, an axial movement is imparted to the piston 6 and hence to the feed-bar 3, which progressively retracts the chasers 1 to conform with the taper of the hole. When the head 2 reaches the bottom of the hole, the bar 22 engages the lever 17 which moves the detent 16 out of engagement with the pin 13 and allows the spring 23 to move the piston 7 away from the head 2. The pin 15 is moved along with the piston 7 and imparts an additional movement to the piston 6 and thus to the feed-bar 3, this additional movement of the feed-bar withdrawing the chasers 1 entirely from the screw-thread in the hole. The movement of the detent 16 away from the pin 13 brings the hook 19 into engagement with the face of the piston 7 and prevents the latter from moving back to its initial position, thus holding the chasers 1 clear of the thread in the hole while the tap is withdrawn, during which operation the spring 23, by means of the linkage 26, 28, 30, moves the pin 21, and thereby the sleeve S, piston 6, and feed-bar 3, towards the chasers 1, thus causing the latter to move radially outwards. The pin 15 traverses the slot 14 in the piston 7 and the slot 9 in the piston 6, but as the piston 7 is held from moving back to its initial position, the pin 15 prevents the piston 6 and feed bar 3 from returning to their initial positions, and the chasers 1 are thus held out of engagement with the thread formed in the hole. To re-set the chasers, the lever 17 is moved to its initial position, thus drawing the. hook 19 out of engagement with the piston 7 and bringing the detent 16 into engagement with the pin 13 and forcing the piston 7 back to its initial position. The pin 15 moves back with the piston 7 and allows the piston 6 and feed-bar to complete their return movement, thereby extending the chasers 1 to their initial position. In a modification, Fig. 2 (not shown), for adjusting the initial projection of the chasers from the rotary head, the coupling connecting the feed-bar and the actuating piston comprises two adjusting sleeves, screw-threaded with right and left hand threads respectively, the feed-bar being entrained by one sleeve and the actuating piston by the other sleeve, and a coupling ring screw-threaded internally with right and left threads mating with the screwthreads on the adjusting sleeves.