An Indirect but Important Danger.

Progress, Volume III, Issue 4, 1 February 1908, Page 125

An Indirect but Important Danger.

A dynamo driven from a car axle is the chief part of the apparatus used for lighting railway carriages in many countries. According to the Electrical Review, the positive danger of drilling holes in the axle when attaching the equipment has not been realised, though it is generally understood to be inadvisable. The fact that a drilled hole will prevent the spreading of an incipient crack is well known, and often taken advantage of. But it does not seem to be as widely known that sometimes a crack may be started by a drilled hole. In any material subjected to alternating stresses cracks may appear where there is an abrupt change of sections; or where a notch bas been made by a cutting tool in a turned suiface. In two recently fractured axles the break occurred through the centre of shallow holes, which had been drilled to recene the point of a set screw. The diameter of the axle fractured was in each case 3 J inches and the breaks occurred after running 15,380 and 13,900 miles respectively. The cracks were several inches from the key-seats, and at points where the stress would not be maximum. As a result of these breaks, set screws have been supeiseded by a pair of clamped plates gripping the axle and bolted to one another. Where axles have been drilled, however slightly, they should be carefully inspected from time to time, to discover any cracks as soon as they appear.

A patent has been granted in Germany for an invention for the manufacture of glass telephone and telegraph poles. A company has been organised and a factory for the manufacturing of glass poles has been built at Gross — Almerode, near Frankfurt. The glass mass of which the poles are made is strengthened by interlaying and intertwining with strong wire threads One of the principal advantages of these piles would be their use in tropical countries, where the wooden piles are soon destroyed by the ravages of insects and climatic influences. The poles are very cheap, costing 25s each pole of 23 feet in length. The Imperial Post Department of Germany has ordered a large supply.