Patent GB-496776-A (GB)
Title: Improvements in or relating to locks for doors
IPC: E05B63/16
Filed: 1937-12-02
Abstract: 496,776. Latches. BACKHOUSE, H. T. Dec. 2, 1937, No. 33407. [Class 44] A latch comprises a bolt normally held projected and two independently operable handles each of which can be moved in one direction to retract the bolt and moved in the other direction to place a positive stop in the way of the bolt to lock it in the projected position. A bolt 4, Fig. 1, is resiliently held projected by opposed springs 16, 18, mounted on the bolt tail on opposite sides of a fixed abutment 21. Handles 5 and cranks 10 are fixed to sleeves 7 mounted on fixed spindles 9. Turning a handle in one direction retracts the bolt and turning it in the other direction locks the bolt in the projected position by bringing the crank 10 to the dead-centre. The cam recess in the bolt is so shaped that during movement of the handle to the locking position the bolt is pressed outwards beyond its normal projected position against the action of the spring 18 until the crank 10 snaps into a recess 17. To prevent locking of the bolt from both sides of the door at the same time, the sleeves 7 are mounted on the spindles 9 by means of quickpitch threads, and, when a handle is turned to lock the bolt, the sleeve 7 moves axially inwards to place one crank 10 in the path of the other crank, so that if an attempt be made to move the latter to the locking position, it cannot reach that position, and is returned to its normal position when the first handle is moved to release the bolt. The spring 18 and recess 17 may be dispensed with, the bolt recess being provided with a spring-pressed ball or a bowed leaf spring past which the crank 10 must be forced as it approaches the deadcentre position. In a modification, the sleeves 7 are fixed, the handles 5 being attached to the spindles 9, which are free to rotate in the sleeves 7 and have square ends engaging square holes in the cranks 10. The boss of one of the cranks 10 and the abutting end of the sleeve 7 are formed with cam faces to move the crank axially as it is turned to the locking position, it being only necessary to provide one pair of cam faces to prevent simultaneous locking by both handles. A compression spring mounted between the inner bosses of the cranks 10 keeps them in contact with the adjacent ends of the sleeves 7. In another modification, there is no axial movement of the cranks 10, a two-armed lever being mounted in the bolt recess to swing horizontally near the end of the cam surface. As a handle reaches the looking position, its crank displaces one end of the lever and turns the other end into the path of the other crank. In a further modification, Fig. 10, a pivoted pawl 54, common to both followers 50, is rotated when either follower is turned to the locking position. The upper end 55 of the pawl then prevents a similar movement by the other follower. A locating pin extends into bores 57 in the ends of the spindles 52, a washer being interposed between the ends of the spindles to prevent the spindle of one follower from engaging the other follower. The pin may extend into one spindle only, the washer, which in this case is integral with the pin, being secured to the end of the other spindle. Simultaneous locking by both handles may be prevented bv a ball housed in a transverse groove in the bolt 4, the end of the follower 50, in the locking position, displacing the ball, which moves to the other end of the groove where it blocks the path of the other follower. In cases where it is desired to lock the bolt from one side of the door only, a grubscrew may be inserted in the wall of the casing, its end projecting in front of the crank to prevent it being moved to the locking position.