One reason why the United States is unable to build a two-ocean navy very quickly is that it takes ten months to build merely the gears of the largest type naval ships, says the "Christan Science Monitor." The gears are the cog-wheels which take the 10,009 revolutions per minute of r ship's turbines and reduce this rotation to perhaps 400 revolutions of theship's propeller.
The length of time in manufacture is due to the fact that the cogs have to be machined to the precisions of a watch, and the big cog weighs about 35 tons. This one is known to sailors as the bull gear. It is nearly eighteen feet in diameter and may carry 600 "teeth."
Each tooth must be cut with a fineness much less than the thickness of tissue peper, with what the engineers call tolerances of 3/10,000ths of an inch.
How the great gears cre made is described by Mr. A. A. Ross of the gear engineering department of the General Electric Company, which is spending $3,000,000 to expand its cog-making works at Lynn, Mass. After the big bull gear is built end ready to have its teeth cut, it is first warmed for several hours to a temperature of 72 degrees Fahrenheit. The room for this warming also is fitted for cooling, in case the huge piece of metal happens io be even z fraction over 72.
After the temperature is right, the gear is moved into the room where the teeth are cut. This room is maintained at exactly 72. Even a slight variation in temperature, by the ex-pension or contraction it would cause in the metal, might throw the teeth-cutting out of true. The monster cog is laid flat on a slowly turning table, and a little device about the size of a bird cage starts clewing out the grooves which will become teeth.
Text read from the printed page and cleaned; old type leaves the occasional error.