one of these instruments. It was invented in the 18th century but did not resemble the tool we use today. It was initially bulky and restricted to the tabletop for taking measurements. As time went on, newer models became more compact and portable and could still provide the accuracy required. It seems simple enough for us today, but where did the idea for this type of precision come from? We had the ruler, didn’t we? Well, that wasn’t enough. It was during the 17th century when it dawned on man that screw threads could be utilized to measure lengths of objects. DUH! 18 threads per inch, 24 threads per inch, etc. In 1638, the English astronomer, W. Gascoigne used the principle of threads to measure the distance of the stars at night. Obviously, he did not directly measure this distance, but he was able to use this principal to fine-adjust his telescope lenses. By using thread displacement, he invented the measuring gauge called the “caliper micrometer.” The principal hasn’t changed. The first patent for a torque
wrench was filed by John Shard of Chicago in 1931. This wrench was used more for measuring the existing torque on a bolt than for actual torqueing. It was similar to todays’ indicating (dial) torque wrench. In 1934 Conrad Bahr and George Pfefferie patented an adjustable- ratcheting torque wrench. Bahr worked for the New York City Water department and he blamed the inconsistent tightness of flange bolts for the water leaks he was required to fix. His wrench featured an audible click and restriction of back-ratcheting when the desired torque was reached. This clicker type wrench uses a clutch mechanism. A ball detent transmits force until the pre-set torque is reached, at which point the force exerted by the spring is overcome and the ball “clicks” out of its socket.
April | May 2020
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