Fig. 2.—Conical hoop flytrap, top view. Letters designate parts as in [Figure 1]
The construction of a cone of any given height or diameter is quite simple if the following method be observed. It is best to cut a pattern from a large piece of heavy paper, cardboard, or tin. [Figure 3] illustrates the method of laying out a cone of the proper dimensions for the above trap. An ordinary square is placed on the material from which the pattern is to be cut; a distance (22 inches) equal to the height of the cone is laid off on one leg of the square at A, and a distance (9 inches) equal to one-half of the diameter of the base of the cone is laid off on the other leg at B, and a line is drawn between the points A and B. With the distance between these points as a radius and with the point A as a center, the portion of a circle, CD, is drawn. With a pair of dividers, the legs of which are set 1 inch apart, or with the square, lay off as many inches on the arc CD, starting at C, as there are inches around the base of the cone, which in this case is about 56½ inches, reaching nearly to the point E. Then add one-half inch for the lapping of the edges of the cone, and one-half inch which is taken up when the cone is tacked in, thus making a total distance from C to E of 57½ inches. Draw a line from A to C and another from A to E, and cut out the pattern on these lines and on the arc from C to E, as shown in [Figure 3]. The edges AC and AE are then brought together, lapped one-half inch, and sewed with wire or soldered. After the aperture of the cone is formed by cutting off the apex, as previously described, it is ready for insertion in the trap.
Fig. 3.—Method of laying out a pattern for the construction of a cone. Cut out on curved line from C to E and on dotted lines from A to C and A to B
In order to figure the distance around the base of a cone of any given diameter, multiply the diameter by 3.1416 or 31⁄7.
The height of the legs of the trap, the height of the cone, and the size of the aperture in the top of the cone, each is of importance in securing the greatest efficiency.