All gears are to be key-seated and finished in accordance with the practice of the best machine-shops. All pinions gearing into the rack and into the large spur-wheels are to be shrouded on top, and the extra strength obtained by this shrouding is not to be counted upon in proportioning the size of the teeth of the pinion.

All shafting is to be of cold-rolled steel, and is to be provided with couplings, collars, and keys for gears.

All couplings must be strong enough to develop the full strength of the shafting, and must be keyed to the same, flange-couplings being preferred. All couplings are to be placed as near the bearings as practicable.

Suitable collars are to be used wherever they are necessary to hold the shafting from moving longitudinally.

The greatest allowable length of any shaft between centres of bearings is to be determined by the formula

where L = the unsupported length in inches, and d = diameter of shaft in inches.

The diameter required for any shaft is to be determined by the following formula:

where d = diameter required, H.P. = the horse-power to be transmitted, and N = the number of revolutions per minute. This will allow for all bending that will come on any well-designed and properly supported shaft under ordinary conditions, and provides for an extreme fibre-stress of about twelve thousand (12,000) pounds per square inch, under the assumption that the twisting moment and the bending moment are about equal.

Every shaft, however, after being designed by the preceding formula must be checked as follows, and if found weak must be strengthened properly either by increasing the diameter or by reducing the lever arm or arms of the bending moment.