CONCLUSION

Illustration No. 33

Typical Bevel Gear Mounting

In 1910 only straight bevel gears were being manufactured. The highest ratio considered advisable was about 5 to 1 unless excessive numbers of teeth were used. Beyond that the number of teeth in the pinion become so small, and the carry-over from tooth to tooth so limited that satisfactory operation was extremely difficult to obtain. There were even serious limitations in machine range when the cutting of high ratios was attempted. With the advent of spiral bevels in 1913 the feature of increased overlap in tooth contact made it possible to use pinions of much smaller tooth numbers, and to obtain smooth action with ratios up to 8 or 9 to 1. A major change was made in cutting machine design as required for producing this type of gear, and at the same time alterations were made which removed the limitations in range for higher ratios, and thus the field of application was broadened. Tooth numbers as low as 5 in the pinion were used satisfactorily in quantity production, and still less were made experimentally. Then in 1925 came hypoid gears. In this type the pinion is usually larger in diameter, and stronger, than the corresponding spiral bevel pinion. This allows the use of still higher ratios without the pinion becoming too small for a bore or shank of adequate size. Ten to one ratios are in common use and higher values are possible. Once again machine design changes were required. Now in the last two years has come the "High Reduction Hypoid." This is a further modification of hypoid gear design, and requires still further range in cutting machines. Tooth numbers as low as two or even one, and ratios up to 100 to one or more can be obtained. Both members of such a pair can be hardened and ground, insuring a high degree of accuracy and very uniform tooth load distribution. Efficiency is high.

Illustration No. 34

A group of bevel gears and mating pinions showing straight, spiral and Zerol teeth

Thus in the period referred to the range of ratios of bevel or hypoid gears available for practical use has been increased from 5 to 1 to 100 or more to 1. In each of the several steps in this progression there were advances made in the type of gear, and corresponding changes in cutting machine design.

Illustration No. 35

Bevel gears as used in farm machinery are exemplified by this application of Revacycle straight bevel gears in a cotton picker.

A further example of this integrated effort is the very much increased rate of production that has resulted. In 1910 an average pair of passenger car rear axle bevel gears of four to one ratio took four or five times as long per pair for the rough and finish cutting operations as the equivalent hypoid gears used today. This is due to the gear design, using fewer teeth in the hypoid pair than in the straight tooth bevels of 1910, and making for a much faster finish cutting method in the case of the ring gear, better and faster operating cutting machines, and faster handling due to hydraulic chucking of the work piece. Much better quality and operating performance are also obtained. Other illustrations could be given of this sort of progress.

Illustration No. 36

Bevel gears have been widely used in variable pitch propellers. Shown here is a set of spiral bevel gears.

We recall a remark at the beginning of this period that the machines being built at that time (about 1910) had already reached their peak. Now as we look back we can see that that was only a starting point, and much more progress has been made since then than previously. We would indeed be lacking in imagination if we failed to recognize that the future offers much more opportunity than the past. We can speak with intimate knowledge only of our own segment of industry, but we believe that the view that we have is typical, and that wherever men with training, experience and skill join together in their attack on such problems it is certain that progress will follow.