This week’s cover shows a circular saw which has no teeth at all and which, moreover, cuts its way through steel much more rapidly than a toothed saw. This saw, in the Swansea works of Sir William Arrol & Co Ltd, is what is known as a friction saw. The steel disk spins round with a peripheral speed of 20,000 feet a minute. The resulting friction of the disk against the work is so great that the metal is burnt away, the saw being fed in as the cut is made. Friction saws are suitable only for work which is not thick, as, for instance, the joist shown in the illustration. For thicker work a toothed saw revolving comparatively slowly is used. The disk of a friction saw is sometimes made of abrasive material.
LINKING NEW YORK AND NEW JERSEY, the George Washington Bridge across the Hudson River was opened for traffic in 1932. Each of the two towers is 559 ft 6 in high from the top of its pier to the summit of the steelwork. The two great piers have their centres 3,500 feet apart. The anchor span on the Manhattan side is 650 feet long, that on the New Jersey side is 610 feet long. The total length of the bridge, with its approach ramps, is 8,716 feet. The headway in the middle is 213 feet above the river. The two towers contain 41,000 tons of steel.
