An Improved Form of Worm Gear.
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WEhave recently received details of an .improved type of worm gear, the product of Messrs. Bostock and Brantley, of Netherton, Huddersfield, in association with Joshua Buckton and Co., Ltd., Well House Foundry, Leeds.
Mr. F. J. Bostock will be remembered 'by many of our readers as the inventor
of that well-known type of parallel worm gear .known as the F.,T.; in which • the teeth of the wheel ware conjugate • to the threads of the worm, not only on the central plane,but on all adjacent parallel planes, thus ensuring correct uniform velocity between the worm and wheel at all points of tooth contact.
This was obtained by means of a, straight-line system of zutomatic generation, as the threads of the worm, instead of being straight-sided on the een. teal plane, are straight-sided on lines drawn from the root to the crest, these lines being tangential to the pitch cylinder and parafle to the lead angle.
Tthe only drawback with this type of worm is its short arc of contact, owing to the fact that the teeth of the wheel rapidly diverge from the threads of the worm, and this can only be remedied by designing the worm with a hollow face shaped to follow the circumference of the wheel and allowing some threads to make simultaneous engagement. with the worm-wheel teeth. Unfortunately, like the ordinary ty-pe of parallel-worm gear, the tooth form of the globoidal
type is theoretically incorrect. To avoid this wrong tooth form, the matheonatical investigation which led up to the construction of the F.J. gear has now been applied to the• globoidal type, and has resulted in the development of what is known by the inventors as the enveloping worm gear, Which is also designed on a straight-lime system of automatic generation.
The illustrations which we publish show the difference between the ordiu
ary F.J. type and the new design, and it has been fomid that the improved teeth contact gives great durability and long life.
Further details of this new gear can be obtained from the inventors, and we shall await with interest any tests which may be conducted either on the road or in the laboratory. Only practical experience can show whether this new type of gearing will stand the test of time over a protracted period.