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November, 1909 'TAE Marine Review S. S. MAURETANIA AND COMPARISON OF RELATIVE SPACES REQUIRED FOR GEARED AND Direct-Drivinc TurBINES. an opening of contact of nearly 1/1000 in. Thus, even under the ex- treme gage errors shown at B, Fig. 6. Messrs. Melville and Macalpine claim that the disturbance of distri- bution of contact pressure is compara- tively slight, and at half. the gage error stated it would be insensib'e. They claim, therefore, that gage er- rors of sensible magnitude do _ not produce a sensible disturbance. Er- rors of erection will be exceedingly minute, so that the only errors to be avoided are those due to unequal wear of the bearings. Any unequal vertical wear will be compensated for by slight tilt of the floating frame. As the forces on the floating frame are inclined to the vertical at only a small angle, vertical wear will take place much more quickly than hori- zontal; and as the inequality of the wear will usually be 'but a_ small fraction of the total wear, it would be almost impossible for sensible angular, error in the 'horizon- tal alignment, such as assumed above, to creep in before the bearings were worn down a long way vertically, and ready for renewal. The case they State is very different if the floating frame is dispensed with, and all the bearings. are cast in one bedplate. any. vey - The worst styipposition is that there is an error of alignment of the axes in the vertical plane. Keeping all dimensions of the gear and bearings the same as in the gear 'built, the resulting "opening of 'contact' -- is, they find, shown by curve A C, Fig. 6. This exhibits extreme sensitive- ness to this error of alignment, as allowable limits will be passed before each vertical gage shows an_ error of 1/1000 in. Such an error would be so small as to be quite insensible to the eye, and would arise even from strongly screwing down one of the holding-down bolts, or from _ slight heating of the bearings, and could not be avoided by the most perfect work- manship. Hence the gear with rigid bearings they hold to be quite im- practicable. Involute teeth have been used, as they give the excellent results shown by the curve A B, Fig. 6. But they have also the well known property that if, through wear of the 'bearings or errors in the original setting up, the axes are somewhat farther apart than designed, the teeth still run true, and there is no "opening of con- tact.' This does not hold with any other form of feeth. » For instance, with epicycloidal teeth the action will not be true if the centers move apart, the axes remaining "parallel: and in these fine high-speed gears a recession of the centers not 1/1000 the designers be quite serious. With this form of teeth also, when the alignment is de- fective, an opening of comtact 6F 1/1000 in., supposing the teeth rigid, corresponds to an error of each end gage of 1/1000 in--that is, a. total error of alignment between the gages exceeding in. would, assert, of 1/50 in., which could hardly be detected. Besides, on account of the way in which openings of contacts occur with epicycloidal teeth, the limit of allowable opening of contact is, it is claimed, much under 1/1000 in. Hence this form of tooth is far in- ferior to the involute on account of its extreme sensitiveness to errors of alignment, and also from the fact that it will not run properly when the axes part even slightly, so that the stresses would be much intensified, and _ the action of the teeth would be noisy. The curve A B (Fig. 6) is tangential to the base-line at A, while for all other arrangements and forms of teeth the curve of opening of contact cuts this base-line at an angte. Hence the solution presented by the float- ,