ALLEN-BRADLEY TOWER CLOCK
According to the Guinness Book of World Records: "The largest four-faced clock is that on the research and office addition of the Allen-Bradley Company. Each face has a diameter of 40 feet, 3-1/2 inches." Dedicated on October 31, 1962, it rises 280 feet from the streets of Milwaukee, and requires 34.6 kilowatts of electricity for lighting and power. The glow comes from several hundred high-output fluorescent tubes, connected by a mile and a half of wire behind each clock face. The clock, pictured at the right, has been sighted from as far as forty-four miles out on Lake Michigan and from Holy Hill, thirty miles away
The minute hands are twenty feet long and twenty-two inches wide at the base, each weighing 550 pounds and using 610 rivets. The hour hands are 16 feet long and weigh 490 pounds each. The hour markings are 4 feet long and 3 feet wide at the base. Seventy-six individual pieces of glass compose each face, most of which are four feet square. Each section is made of two pieces of a glass separated by a thin plastic film. Assembled, each face includes 3,900 pounds of glass, and 1,600 pounds of aluminum border members.
Each face of the clock is independently operated with its own gearbox. Two motors power each gearbox, one for driving the clock and one for advancing or retarding the hands. The motors are connected to clock via a planetary gear system, with the larger motor driving the ring gear and the smaller, reversible squirrel cage motor with a magnetic brake able to keep the time accurate by adjusting the speed of the sun gear. Details of the mechanism are displayed in the original patent (pdf). By using a squirrel cage motor, the clock can be set either ahead or back at a rate of around one hour per minute, without disconnecting the clock from the main drive. The gear design also prevents backlash through the gear system, a vital need given the size of the clock hands.
A second patent (pdf) was directed to the clock hands, which describes the construction that was necessary because of the particular use and consequential size. The construction provides telescoping open-faced sheet metal members attached to one another as needed. The configuration permits considerable reduction in weight of the respective hands as well as providing a construction capable of withstanding considerable sidewise thrust during high winds.
The original plans for the clock tower date as far back as 1959, when it appears on early drawings for the proposed addition. Created by architect Fitzhugh Scott, the plans included several towers in its design, only one of which would house a clock. This was scaled back, however a smaller tower on an existing building was kept and modified to display the outdoor temperature using a large digital display. The interest in creating the tower was Harry Bradley, younger of the firm's two founding brothers. An inventor, Bradley including in his tinkering several of the clocks which he owned.
The patents for the clock tower, however, went to others. For the clockwork, the patent was awarded to Gerald W. Lohf, Philip F. Walker, and Alonzo Ray Ellsworth. That for the hands was awarded to Walter S. Freeberg and Mr. Ellsworth.