Automatic centre punch

An automatic center punch is a hand tool used to produce a dimple in a workpiece (for example, a piece of metal). It performs the same function as an ordinary center punch but without the need for a hammer. When pressed against the workpiece, it stores energy in a spring, eventually releasing it as an impulse that drives the punch, producing the dimple. The impulse provided to the point of the punch is quite repeatable, allowing for uniform impressions to be made.

The patent history of automatic punches indicates two principal goals for the development of the tool: repeatability of impact, and convenience of operation. Other desirable properties include low recoil when triggered, ease of adjustment, and reliability.

A number of designs for automatic center punches have been developed since the late 19th century as improvements over punches requiring the use of a striking tool. The earliest types were not fully automatic, using a captive weight lifted by the user or a spring and weight drawn by the user to provide the striking impulse. A number of patents have been issued for these designs, and they continue to be referenced in patents into the 21st century. There are also a number of examples of hammer and punch combinations intended for one-handed use, but being modeled upon a conventional hammer striking a separate punch tool.

The earliest US patents for the modern automatic center punch were filed during 1904 by Hartley and Stryhal for designs using a leaf spring catch to release the hammer, both assigned to Brown and Sharpe. In 1905, Seitz patented a manually triggered punch that has many of the internal structural elements of some later fully automatic models, and Spalding was granted a patent in 1908 on an application filed in 1904 for a different design of leaf spring controlled fully automatic punch that included easy adjustment of blow as well as interchangeable, threaded on points.

Adell and Baltzer, of L. S Starrett Co., patented a design with concentric shells and pins in cam slots as the triggering mechanism, and Adell and Starrett received a 1907 patent for a design using a sliding block actuated by a tapered bore in the body to hold back the hammer.

Some of the modifications introduced in the Seiler patent of 1923 saw substantial manufacture in the United States, and this patent has been referenced by other patents into the 21st century. This design uses a sliding block similar in concept to the Adell and Starrett patent, but with a coil spring to return the sliding block rather than a leaf spring, but a more involved scheme to slide the block to release the hammer.

...
Wikipedia