SPLITTING HAIRS

Sun (Auckland), Volume I, Issue 154, 20 September 1927, Page 7

SPLITTING HAIRS

ERRORS NOT ALLOWED MARVELLOUS MACHINES A hair’s breath. To most people this denotes the extremity of thinness, although in reality it is twice as thick as a cigarette paper, which measures a 2-1000th part of an inch. A visiting card is quite a bulky affair in comparison, as it is no less than 25-1000ths of an inch thick. Thinness, however, is merely a matter of comparison, and to the engineer aiming at extreme accuracy the splitting of a hair or even a cigarette paper is quite an every-day affair. For instance, an error of l-1000th part of an inch is all the margin allowed in many of the larger and clumsier parts of a modern motor-car, this fine limit accounting for the long life of the better-class cars. "When it comes to other and more vital parts, such as the gear wheels, being registered in such up-to-date works as Morris Motors (1926), Ltd., an error only 2-10ths of a l-1000ths part of an inch is allowed, the amount at Cowley, England, for instance, by an instrument that can read to l-10th of a l-1000th. In otner words, the degree of thinness measured by this marvellous instrument is equal to the splitting of a cigarette paper into 20 layers! Another aspect of the case is presented by the fact that the ordinary film of oil that separates, say, the crankshaft and its bearings is quite a fat affair measuring some 3-1000ths of an inch. To attain these extraordinary fine limits grinding and lapping machines are employed. In some cases, despite their marvellous dexterity, they are automatic in action, the operator has only to set the machine to take off material up to a few thousandths of an inch. The machine not only performs this work, but stops itself when the job is completed. FINED FOR MUD SPLASHES Motorists of Montreal, Canada, are fined for splashing mud on pedestrians while passing through _t>ools of water at a high rate of speed. The bigger the splash the larger the tee- ;