SILENT ROAD DRILL

Wairarapa Times-Age, 6 May 1940, Page 2

SILENT ROAD DRILL

AN ENGLISHMAN'S DISCOVERY. The work of Mr Walter Pettit, a consulting engineer of London, will soon be seen in the city’s streets. Everyone hopes that it will not be heard. Deafened and annoyed by pneumatic drills operating below his office window nearly three years ago, Mr Pettit decided that the time to rid the world of their terrible noise, ' had come. He discovered that the noise made by the pneumatic drill was 117 phons, and decided that it should not be more than 90 phons, or about the same as loud music.

His experiments cost him £2,500 before he achieved success. He encased the drill in a double sleeve of steel something like a vacuum flask, the space between the two walls stuffed with shredded wood four inches thick. Holes like those in a colander were made in the inner wall, the noise of the internal mechanism of the drill and the noise of the exhaust passing through them'into the shredded wood were to a great extent absorbed.

The handle and the point projected at each end, but the drill still made much noise as it sank into the ground. After many fruitless attempts at eliminating this nuisance, the inventor decided to let the casing stand firmly on the ground, keeping in all the sound, while the drill inside slides up and down so that it can move downwards as it drills. The outer shell thus stands on the ground, a rubber edge making it almost sound proof. This new drill is completely inaudible above the noise of traffic at a distance of thirty yards, and people on the ground floor with the drill just outside their windows are able to talk and work.