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° 16 THE MARINE ing units for the battleship NEVADA which have been in service for some time and shown good results. Among the ship equipments not yet completed are included the propelling machinery for Destroyer No. 69, built at Mare Island, and new propelling machinery for the scout cruiser SALEM. In all of this practical experience no case of trouble with gearing has developed and no appreciable deterioration of gears has been observed. One of the important reasons for adopting this type of gearing was that its design tended to afford a distribu- Section A-A Loohirg 117 Divectior? of Arrows in this gearing is simple. The gear is built up of a number of plates ma- chined to a form which gives them the desired degree of lateral flexibil- ity. These plates are put together, engaging solidly at the hub and also engaging on a narrow edge at the periphery. When so built together they form a solid cylinder which can be spirally cut in the ordinary man- ner. After cutting, the edge engage- ments are relieved with a small divid- ing tool so that each disc operates independently and is free to deflect laterally under the side pressure which a8 Seta PENS Nsom sheet 9 {SSE Nw REVIEW January, 1917 place, where gears are inflexible there must always be a tendency to increase strain at the loaded end of the pinion through torsional deflection of the pinion. There is also a tendency to inequality of strain on different parts of the surface through the la- teral deflection of the pinion un- der load. These inequalities can be partially compensated by elevating the bearings or evening the pressure on the bearings, but this compensa- tion can only be partial because the correction applies only to the two ends and not to the middle. Further- Section BB Loonirg iin Direction of Arrows FIG. 3—ASSEMBLY DIAGRAM OF CURTIS GEARED TURBINE ONE-PLANE TYPE FOR MARINE PROPULSION tion of strains and means by which excessive strains would not be im- posed upon any part through slight imperfections, distortions or inaccura- cies. The uniform success which has been accomplished with an entirely new product shows that this expecta- tion has been amply justified. Some of the gears which have been used have been very imperfect, both in the matter of material and workmanship, and have been used under extremely trying conditions. That they have not failed has afforded the strongest evidence of the general reliability of the method. The character of construction used results from its diagonal engagement with the pinion. The parts are so pro- portioned that this lateral deflection can at no time involve fiber strains which could possibly cause destructive fatigue. A very small amount of this lateral deflection is sufficient to afford the desired distribution of load and this amount can easily be given with- out approaching dangerous periodic strains. Inequality of Strain To appreciate the value of this flex- ibility and load distribution, various peculiarities of solid and spiral gear- ing must be considered. In the first more, the momentary and _ periodic . Strains on different points of solid spiral gearing may be seriously af- fected by vibrations of supporting structures, irregularities of machine work or gear cutting and other causes. If for any reason such conditions cause any tooth or part of a tooth to receive periodically excessive strains, fatigue may result and a broken tooth may destroy the whole gear. To obviate the possibility of break- age under such conditions, it is often desirable in solid gearing to use rela- tively large teeth in order that these possible irregular strains on teeth or pote onl b= oe aa