Giant Testimony

Perennial sculpture exceeds 12-million cycles

Outside the Seattle art museum stands a 48-foot high hollow steel sculpture, designed by artist Jonathan Borofsky to represent “the worker.” Since 1991, between the hours of 7 am and 10 pm, this statue has been in daily operation at a rate of 4 hammer strokes per minute, except a single day’s respite per year — Labor Day, of course — with nary a missed beat. That’s more than 12 million strokes accumulated over the past eleven plus years without any problems from the gearbox.

Jim Virmala from Cone Drive, a division of Textron Power Transmission, Traverse City, MI, dealt with the original installation in 1991. He explains, “The designers wanted a gearbox that would operate in a quiet and smooth manner, but would be rugged and durable as well. A double enveloping worm design, where the worm and gear wrap around each other, was a clear favorite due to its high torque capacity and ability to handle heavy loads.” The double enveloping design increases the gearbox’s load carrying capacity, providing concomitant increases in tooth area contact and number of teeth in mesh as compared to other worm gear designs. Thus, the design provides higher torque capacity without an increase in size, high shock resistance and the ability to withstand heavy starting and stopping loads. There is low backlash, owing to the inherent precision of the double-enveloping design. All of which contribute to increased durability and longer gear life. Simply stated, a Cone Drive speed reducer is a small machine doing the work of a big one.

For this particular application, a gearbox with a ratio of 450:1 was provided with special breathers to cope with the outdoor environment. The Hammering Man’s Brobdingnagian proportions required that the arm be tested whilst he was lying down, thereby forcing the reducer to be capable of operating in both horizontal and vertical positions.

There was a near disaster during installation in which one of the support slings snapped, causing all 20,000 lbs of steel to fall several feet to the ground. A few bolts on the linkage sheared, but there was minimal damage to the reducer itself. The sculpture has been operating since without a hitch.