Patents: Pocket-Knife

The company Heinrich Kaufmann & Söhn in Solingen was established in 1856 and existed until 1995. The company made all kinds of cutlery, from pocket knives to surgical instruments. Shortly after 1900, Ernst Kaufmann (maybe Heinrichs grandson) patented a fascinating range of methods of locking rotatable blades, including the one presented here, protected by U.S. patent 736524, that was granted in August 1903.
Kaufmann’s idea was to make a knife with “a device for locking the blade of a knife in the open or closed position, consisting of a part which is so hidden in the knife or is formed externally in such a manner that persons not in the secret will be unable to discover the right way of using the same […]” .
This was achieved by the following construction:
The blade of the knife had at its lower end a notch (l) in which the spring (f) engages with its hooked end when the blade is open. The rear of the spring is attached to the knife handle and in its centre part it has a slot for a stud (p). This stud limits the movement of the spring. A small lever (h) is pinned to the front of the spring. The lever has a shoulder (r) at the rear. The lever folds down  flush with the back of the spring. To open the blade, the lever must be pulled out by means of the shoulder, lifting the spring from the notch. The same procedure applied to fold the blade.
Kaufmann suggested several varieties of this construction: “It is obvious that the lever h may be so formed as to impart to it the shape of a tool or of a manicuring implement or the like […] The lever may also be made of fork shape at the end where it is connected to the spring and the back of the spring may be recessed somewhat at that place, so that the lever in covering the spring may fit in well.”

The drawings from Ernst Kaufmann’s U.S. patent 736,524. The application was filed on 14 November
1902, the patent was granted on 18 August 1903. Figures 1, 3 and 4 show a side view of the knife
with the blade in different positions. Figure 2 is a view from the spine when the blade is opened,
and figures 5 and 6 show detail views of the lever.