The following letter is in response to an article in our January issue that showcased a 1925 Lanchester 40HP Tourer that ran into car trouble involving its rear axle worm and wheel.
I enjoyed reading about the Lanchester repair in your January issue. Dr. W.F. Lanchester and his brother George built the first all-British automobile in 1897, which featured an epicyclic gearbox. It was also the first auto with a differential rear axle. The Lanchesters were gear pioneers and built hobbers, including the first British worm gear hobber in 1893. One of these hobbers can be seen in the Birmingham Museum in England. They also built a grinder for hardened steel roller bearings that was accurate to 0.0002 in.
In 1910, Dr. Lanchester designed a globoidal worm for use in the rear axle of his cars. The included angle varied as did the depth: Single threads were 29°, double and triple 35°, and quadruple 37.5°. Small, multiple-thread worms could have angles as high as 52°. The sides of the teeth sloped 1:2 and were considered the most efficient of the time. Efficiencies were tested at the National Physical Laboratory, Teddington, U.K., on a Daimler-Lanchester machine installed in 1912. Tests for the Daimler Company concluded that efficiency was dependent on the condition of the oil film. Full details with diagrams and photographs of Lanchester's test machine are in the book Mechanical Testing by R.G. Batson and J.H. Hyde, published in 1923 by E.P. Dutton & Co., New York.
William P. Crosher
Mt. Pleasant, S.C.