during a complete revolution of the shaft is the eccentricity measured in thousandths or ten thousandths, as the case may be. There are bearings of all degrees of tolerances on the market from poorest grade bearing, such as is used in baby carriage wheels, to the highly specialized bearing, such as is used in gyroscopic wheels. The degree of perfection is also an indication of the price, so that it behoves the designer to get the proper bearing for the work; i. e., be satisfied when he gets a bearing that runs smoothly and does not wear out quickly. BEARING TO BE TESTED MASTER BEARING ECCENTRICITY-ZERO MEASURING GAGE SKETCH 16. In determining the tolerances of ball bearings for a certain machine, bear in mind the following: 1. Avoid vibration, as it shortens life of bearing. 2. Vibration is caused by inaccuracies of races or balls. 4. That perfect bearings will vibrate with load dynamically unbalanced. 5. With inaccurate bearings, the higher the speed the greater the vibration. 6. That the proof of the selection is a smooth running bearing. 7. The life of a bearing depends on the quality of the races, balls and retainer-a breakdown in any one of which will destroy the bearing. KIND OF LUBRICANT Oil is the greatest friend, and dirt the greatest enemy of the ball bearing. The lubrication of a ball bearing is absolutely necessary. A thin film of oil has by practice given the best results. Too much oil causes friction, but the heat is carried off by the oil and immediate bad results do not arise from this source. The main objection to too much oil is that the oil becomes broken down. rapidly, thus losing its lubricating qualities, which entails loss. of money and labor. Too little oil results in friction and damage to bearing by over heating. Two general kinds of lubricant are used: Grease and oil. It is necessary that either kind be chemically neutral, to prevent rusting of bearing. Grease is used where it is necessary to close in bearing with no chance of oiling. This method is used in high-speed grinding machines of 30,000 r. p. m. Oil is probably the best lubricant. A light grade oil, such as Arctic engine oil, has proven successful in medium and highspeed machines. It has good chemical qualities and can stand temperatures to 400° F. One thing that must always be kept in mind is that the lubricant must be kept clean, as dirt reduces life of bearing. METHODS OF LUBRICATION There are many methods of lubrication. With grease in use the bearing is packed in grease. With oil lubrication the lubricant is transferred to the bearing by surface attraction (wick method), by splash or by oil rings. The wick method is the most efficient, as the oil flow can be accurately determined by the number of strands in the wick and all oil reaching the bearings is filtered. The wick should not touch the moving parts of the bearing, otherwise the filtering feature is destroyed, as lint would be carried into the bearing. Oiling rings and splash system have two disadvantages: Firstly, they break up the oil, thus shortening its life; and secondly, they do not filter the oil and tend to flood bearings with oil sediment and chips from oil rings. SUMMARY In summation, the points to be borne in mind in reference to choice and use of bearings are: 1. A ball bearing has less friction than ordinary bearing. 2. Two-point contact bearing best. 3. For high speed use retainer type bearing. 4. For low speed, heavy load, use full ball type bearing. 5, Slotted type bearing objectionable where there is end thrust. 6. Double or multiple row bearings not so satisfactory as 7. Use bearings with 300 or 400 per cent safety factor. 10. Long life for high-speed bearings depends on load and accuracy of bearing. II. Radial bearings should not be subjected to more end thrust than 10 per cent of designed load capacity. 12. Use self-aligning bearings where perfect alignment is not essential. 13. Lubrication of ball bearings is necessary. 14. Too much oil is better than too little oil. 15. Wick oiling best. [COPYRIGHTED] U. S. NAVAL INSTITUTE, ANNAPOLIS, MD. THE ELECTRICAL DIVISION ABOARD SHIP By LIEUT. COMMANDER ALEX. M. CHARLTON, U. S. Navy The electrical division aboard ship has grown, like Topsy, without much fathering or mothering until very recent years. It is the purpose of this article to trace the growth of the electrical personnel aboard ship from its beginning to its present organization, which is believed to be the logical and ideal one for the proper performance and upkeep of the electric plant. Electricity for lighting purposes was first introduced on a man-of-war in 1883, when the U. S. S. Trenton was equipped with an Edison lighting plant. Before this time electricity supplied by batteries had been used for call bells and annunciators, and small hand-generating sets for the firing of torpedoes (mines) and guns. The power of these devices was, of course, negligible. The dynamo of the Trenton was installed at the navy yard, New York, under the cognizance of the Bureau of Navigation, although the Bureau of Ordnance agreed to pay half the cost of the labor and material to fit the dynamo engine with steam and exhaust piping. The cognizance of the Bureau of Navigation over electrical apparatus was established even before electric lighting had been installed on any naval vessel. It (the Bureau of Navigation) shall furnish signal lights, running lights and standing lights on board vessels, including electric apparatus for lighting purposes.-General Order 293, March 30, 1882. The rating of electrician was established in November, 1883, shortly after the Trenton's plant was completed, at a rate of pay of $50 per month. (General Order 310, November 17, 1883.) After being in existence two months, however, the rating was abolished (General Order 315, January 5, 1884). As men trained for seamen gunners at this time received instructions at the torpedo station, Newport, in electrical matters, it was apparently decided that a special rating was not necessary for the upkeep of the plant on the Trenton. The engine and dynamo of this plant were very ruggedly built and required little attention. Reports made during the year following their installation say nothing of engine or dynamo trouble. The office of Naval Inspector of Electric Lighting was established in January, 1887. Lieut. Commander R. B. Bradford was the first inspector. He had performed much the same duty for some time previous, and as executive officer of the Trenton had supervised her installation. During this early period, while dynamos were being installed for lighting purposes by the Bureau of Navigation, the Bureau of Ordnance was also installing dynamos for use with searchlights. The searchlights were operated from series-wound machines giving about 50 volts, and the incandescent lamps from shunt-wound machines giving various voltages from 70 to 110. With the introduction of the compound-wound dynamo, both searchlights and lamps could be operated from the same machine. The divided cognizance (ordnance and navigation) brought in various types of dynamos, engines and appurtenances, and it soon became apparent that one bureau should have the cognizance of all electrical material. This was done in 1889 when the Bureau of Equipment and Recruiting was given cognizance of all electric appliances aboard ship. The responsibility for the care, preservation, efficiency and working of all electric apparatus on board ship rested with the navigator. He had seaman gunners and gunners' mates to stand watch on the dynamos and repair the circuits. These men were given a certain amount of instruction in electricity at Newport, but they did not specialize in that subject. The need for specially trained men became apparent as electricity was extended to other uses besides lighting, such as signal sets, interior communication and telephone. On account of the steadily increasing demands upon the electric plant of a ship and its consequent extension to meet the requirements, the care and attention necessary for efficiency is also growing. In view of this fact, it is respectfully recommended that the rate of electrical machinist be |