A Simple Telegraph Key
by Arthur R. Nilson, McGraw-Hill, New York, 1942
A professional looking radio key can be made by the beginner or experimenter at a cost of a few cents for parts. This key is very satisfactory in every respect, as will be seen from Fig. 15. It is made of a short piece of 1-inch-square brass rod and a few other parts easily procurable. Its construction is clearly shown in the mechanical drawings, Fig. 16. As exact dimensions are shown in the drawings, no difficulty should be experienced in making this key.
FIG. 15. — A homemade key. This key is very inexpensive to make and utilizes tungsten contacts.
A unique way of providing contact points that may be easily renewed when necessary by the ingenious builder is to use ignition contact points. These points may be obtained from almost any automobile supply store or direct from Sears, Roebuck and Company by mail. These points are usually listed in the mail-order catalogue indexes as Contact points, auto.
The point mounted on the circular-ended spring is used for the bottom contact as shown in Fig. 15. The other contact is removed from its spring by filing off its back and is soldered to the upper contact screw which passes through the arm of the key. A slight indentation is provided in the end of this screw by marking it with a punch and drilling, first with a small drill (about No. 38) and later with a slightly larger drill. The stem of the contact should fit into this hole to provide a support for the contact. The screw is then screwed through the arm, turned over, and held in position for soldering the contact to it. First tin the screw, and then put a speck of soldering flux on the back of the contact. With a pair of tweezers, hold it in position on the end of the screw, and apply the tip of the soldering iron. In a few moments the solder applied to the screw will melt and hold the contact firmly. The contact may now be cleaned off around its edges with a file, a excess solder being thus removed. It is now ready for use.
FIG. 16. — Mechanical drawing of homemade key.
The side thrust screws are drilled out at their ends, as shown in the magnified view of these screws in Fig. 16. The bearing rod on which the key arm swings is pointed at both ends and thus fits snugly into the thrust screws. An easy way to bring the bearing-rod ends to a point is to fasten a hand drill in a vise so that it may be turned with the right hand. The bearing rod is then fastened in the drill chuck and the drill rotated by turning the crank. With the left hand, hold a flat file against the end of the rod to be pointed. In a short time the file will bring the rod end down to a point. The rod is then reversed and the opposite end pointed in the same manner.
An excellent key knob may be made from the top of an ink-bottle cork. This knob is shown in Fig. 15. Remove the cork from the composition top, and scrape it clean, leaving only a shell. Next, solder a l-inch 8-32 flathead machine screw to a piece of circular brass or copper just large enough to fit into the composition top. Turn the top upside down, place the screw assembly in position, pack the knob with a plastic cement such as plastic wood or Tilette , and allow to harden. The knob is now ready to be screwed into the key arm. If desired, a regulation key knob may be purchased.
The key base may be finished with mahogany-varnish stain or in some other suitable way to suit the taste of the builder. When the key is ready for final assembly, the brass parts should be carefully polished. If possible, these parts should be given a coat of clear lacquer which will keep the key always looking bright and clean. The constructional work required to make this key will become clear from studying Figs. 15 and 16.