Patents: A folding knife with a one-piece handle

How do you make a folding pocket knife with a spring and a one-piece handle? Johann W. Bierenbach from Solingen, Germany, found a rather ingenious solution for which he was granted German patent 360311 in June, 1921.
Johann W. Bierenbach is something of a mystery. His patent says he lived in Solingen, but there is no mention of him in J. Anthony Carter’s ‘German Knife and Sword Makers’. His folding pocket knife with a one-piece handle is the only patent we have found in his name, so that side of the story is a dead end. Which leaves us with the invention itself.
Bierenbach’s basic idea was to have a slip-joint folding knife with a one-piece handle, which could be manufactured cheaply. The handle could be made of wood, horn, metal or any other suitable material. The handle would have a slot with two short liners, to accommodate the folded blade. The upper part of this slot contained the spring, which would provide the necessary friction to prevent accidental opening or closure of the blade. The rear part of the handle had a longitudinal bore, in which the round tail part of the spring would be inserted, which was then riveted to the rear end of the handle. The blade would be attached to the handle in the usual manner, by means of a pin.
As an extra support, Bierenbach had supplied the liners with two lateral sheet metal extensions, which were bent outwards around the handle. These extensions were fastened to the handle and the spring by a rivet (i), so that all parts of the knife were held firmly together. According to the patent description, the pocket knife could have one or more blades, with or without a corkscrew or other pocket tools. It could also be made as a bread knife or butcher's knife. Bierenbach even included a production sequence:
“The metal liners c are inserted into the finished handle a, then the spring d is inserted and the rivets f and i attached. Then the knife blade b is hinged and fastened. […] The whole pocket knife therefore consists of only a few parts and can be manufactured in a simple and inexpensive manner.”

The drawings with German patent 360311, for Johann Bierenbach’s folding pocket knife with a
one-piece handle.A. Handle; b. Blade; c. Liners; d. Spring; e. Handle bore; f. Rivet; g. Blade pin;
h. Liner extensions; i. Rivet; k. Support plate.