The Nail Clipper: Spring Jaws and a Cam Lever

Their device "consists, essentially, of a pair of nipping-jaws composed of a single plate of spring-steel so formed and bent as to bring its cutting-edges in opposition and nearly in contact", with "a yoke secured to one jaw" giving a pivot to "a cam-headed lever, whose operation presses the jaws forcibly together." Plate A is bent to a U so the jaws "stand normally some distance asunder". On the yoke B pivots the lever C, whose depression forces the jaws together until they meet; on release, "the resilience of the jaws causes their automatic separation". Part of the lever's back is grooved or roughened "to constitute a file or rasp"; its end G is a hook "suitable for buttoning gloves"; a clasp E holds the lever closed and a bail F hangs it from a watch-chain. They note earlier trimmers with two hinged jaws held open by a spring and closed by the thumb and finger, "and we therefore disclaim invention, broadly"; they claim the one-piece jaws closed by a cam-headed lever.

Take a lever-type nail clipper apart by pulling out its pin. Identify the U-shaped jaws, the lever and the part of it that acts as a cam, and the pin that is the pivot. Measure with the caliper the lever length from the pivot, how far the jaws close, and how far the lever's end travels, and work out the ratio. Reassemble it. Hang weights from the lever's end over a strip of card in the jaws until it cuts, and compare the force with the notebook. Check the jaw edges under a hand lens: they must meet along their whole length.

**Eugene Heim and Celestin Matz** of Cincinnati filed US 244,891 on 9 June 1881; it is dated 26 July 1881. They claim jaws of a single integral piece of steel, held open by their resilience and closed by a cam-headed lever. **Honest limits.** The nail-cutting force, jaw stiffness and friction efficiency in the notebook are assumptions; the patent gives no dimensions.