1. Field of the Invention
The present invention relates to an eyeglass frame having metal-and-string rims.
2. Description of Related Art
An eyeglass frame having metal-and-string rims is well known as one type of eyeglass frame. As shown in FIG. 9, it has two upper half-rims of arc-shaped metal wires "a" and two lower half-rims of high-tension strings "b" to encircle and hold associated lenses "c". The upper half-rims of arc-shaped metal wires "a" are connected by an intervenient bridge "d", and each upper half-rim "a" has a temple hinged thereto via an associated temple-joint "e".
The upper half-rim "a" is made of a possible thinnest wire, say 0.6 millimeters in diameter, in the hope of making the upper rim least noticeable and, at the same time, expanding the visual field to the possible extensive limit. In almost all cases the rim wire is contained completely in the circumferential groove of the lens. Likewise, the string "b" is contained completely in the circumferential groove of the lens, and this requires that the diameter of the rim wire be equal to that of the string "b". Such a thinnest rim wire, however, can have no sufficient strength for the eyeglass frame. Also, disadvantageously the intervenient bridge and the opposite temple-joints cannot be soldered directly to the rim wire because it is not exposed from the circumferential groove of the lens "c".
The upper half-rim "a", therefore, has reinforcement pieces "f" soldered to its opposite ends, and the bridge "d" and the temple are soldered to the opposite outer-reinforcement pieces "f" of the upper half-rim "a", which opposite outer-reinforcement pieces "f" are curved and laid on the circumference of the lens "c". The reinforcement pieces "f" have an increased strength compared with the rim wire, and therefore, the force applied to the frame is liable to be concentrated to the boundary "g" between the reinforcement piece "f" and the upper half-rim "a". As a result, the frame is often broken at the rim-to-reinforcement joint boundary "g". The rim wire portion lying under the rim-to-reinforcement joint boundary "g" was heated and softened in soldering, and therefore its strength was lost significantly. Sometimes the lens is so badly stressed at the rim-to-reinforcement joint boundary "g" that it may get a crack there.
As for the high-tension string "b" each reinforcement piece "f" has two small apertures made on its lower end, and one or the other end of the string "b" threads these apertures as seen from FIG. 10 before being fixed to the reinforcement piece "f". The string "b" is stretched to allow the aperture edges "h" to somewhat bite the string "b", thereby preventing the slipping-off of the string "b" from the apertures. As a result, however, the string "b" is likely to be cut there sooner or later (see FIG. 10, "h").
Such an eyeglass frame having metal-and-string rims is displayed for sale with dummy lenses fitted therein, and when sold, the dummy lenses are replaced by real lenses. At the same time, the strings "b", which are supposed to have scars made by the aperture edges "h" of the reinforcement pieces "f", must be replaced by new strings. The breaking strength of the string "b" is measured to be approximately 3.6 kilograms when the string is bent around the aperture edge "h", thereby allowing it to bite the string "b".