Patent GB-551554-A (GB)
Title: Improvements in screw thread cutting mechanism
IPC: B23G7/00
Filed: 1941-07-25
Abstract: 551,554. Screw-cutting dies and taps. LANDIS MACHINE CO. July 25, 1941, No. 9461. Convention date, Aug. 2, 1940. [Class 83 (iii)] A screw-threading tap or die comprises cutting elements 24 positively adjustable in the body 20 by lever mechanism actuated during operation to produce tapered threads, the lever being pivoted to a normally stationary member and having spaced camming contacts with members slidable relatively to the body. The head 21 of the body carries chaser assemblies 24 arranged for a tapping operation and are moved radially by a sliding cam 27 having cam grooves 28. The cam is secured to a plunger 26 which can slide within a collapsing sleeve 25 sliding in the body. A slot 31 accommodates a pivot assembly 32 which comprises a lever 33 sliding through a split trunnion assembly 82, mounted in the plunger 26 and also through a trunnion 35 mounted in the control collar 36. The latter is secured to an oil shroud 38 and to a work-engaging ring 37 by which the collar is moved back during operation, the collar then acting on the lever 33 and imparting reduced movement to the plunger 26 and cam 27 to produce a tapered thread. The lever assembly includes a support 51 secured to the sleeve 25 and carrying a slidable taperadjusting member 54 which can be locked by a screw adjusted wedge 63. The member 54 has a threaded portion 57 coacting with a nut 59 which may also be externally threaded into the support 51. The lever 33 is in two parts 72, 73 connected by the pivot pin 75 of the member 54. so that when the control collar is moved back, a reduced movement is imparted to the cam 27 through the trunnions 82 as the lever turns on pivot 75. The taper may be altered by adjustment of the pivot by nut 59, this adjustment having no effect on the setting of the chasers. An indicating device is associated with the screw 57 for showing the amount of taper. The pivot 75 may be adjusted so that it is coaxial with the trunnions 82 in which case movement of the collar has no effect on the position of the plunger and a parallel thread is produced. To adjust the chasers for size the cam 27 is recessed to receive the head of a bolt 92 screwing into a sliding connector 104 which also receives a bolt 97 axially fixed to the plunger and rotatable by a wrench to move members 104 and cam 27 to set the chasers. To remove the chasers the bolt 92 is rotated until the cam grooves are moved outwardly clear of the chasers. The collapsing sleeve 25 is urged rearwardly by a spring 96 and is normally locked by a latch 125 engaging a face 120 of end member 45. A length-determining member 121, Fig. 9, is adjustably secured to the collar 36 and carries a roller 123 which, at the end of the required travel, engages a plunger 124 to disengage the latch and allow the spring to move back the collapsing ring. The plunger 26 and cam 27 are also moved back thus collapsing the tap. To reset the tap the collar 36 is returned by hand-actuated pinion-gearing operated from a crank, thus entraining the pivot assembly and collapsing-sleeve until latch 125 engages behind the shoulder 120. The lever 33 during its movement operates a sliding cover-plate 133 to protect the body slot 132 against the ingress of dirt &c. Specifications 343,834 and 498,779, and U.S.A. Specification 2,024,278 are referred to.