In the August issue of Motion System Design, we presented the mystery of the centrifugal mercury clutch. The design was patented in 1950 by Automatic Steel Products Inc. of Delaware, and featured in the 1959 advertisement pictured at right. In the clutches, heavy liquid metal swings into a chamber to apply force for consistent torque. These are no longer sold commercially.

Reader Donald Hesprich, senior project engineer at the Salisbury Machinery Div. of Oliver Rubber Co., has provided some clues as to the eventual fate of mercury and other centrifugal clutches:

“When I was a kid in the 1960s, I had a minibike that had a Mercury Automatic Clutch. I don't know whether it had mercury in it or not, because I never took it apart. But it was a centrifugal clutch, and was manufactured by Mercury.” Hesprich reports that the neighborhood kids all detested the centrifugal clutches, as they would often slip. “We wanted the spring-held clutches of motorcycles or cars.”

He got his wish eventually: “When I got older, I had a car that I dragraced, which had a clutch in it that caused my left leg to grow strong because of all the force it took to push the pedal down. It took a big spring force to transfer all the power from that big block. I often wondered how the Top Fuel and Funny Car guys managed to push down the clutches that restrained their 5,000-hp beasts.”

Lo and behold, they were using multi-disc centrifugal clutches. “Now we see six and seven-disc centrifugal clutches controlling the 8,000-hp fuel cars in the National Hot Rod Association,” says Hesprich. “I would have never thought it.” In short, the centrifugal clutch shaft connects to the motor; as that motor increases speed, attached weights swing outward and push friction pads into an engaging surface. Then the two parts spin as one.

Next mystery: Abart Gear and Machine

Featured in our October 1959 issue of Motion System Design is a company called Abart Gear and Machine. What we know: The operation was acquired by Cleveland Gear Co. in 1984. Some of Abart's designs are featured in later patents, and one of Abart's CEOs, Robert Bergmann, later became president of the American Gear Manufacturers Association. Do you have any other information on the company or how its gears are still used? If so, email us at msdeditor@penton.com, and we'll send you a copy of The Universe in a Nutshell by Stephen Hawking.