How can you cut glass under water?
Using scissors to cut glass; by K. Karmarsch.
It has long been known that thin sheet glass can be cut with ordinary paper scissors if it is kept a little deep under water. The water obviously has the purpose and use of softening the vibrations or shocks of the glass and thus preventing it from shattering. I have tried the procedure several times, but convinced myself that the cutting edge is always very rough and jagged, and that one | 233 | is not completely secured before the glass panel cracks in two. Serious, i.e. practical-technical application has therefore hardly ever been made of the little feat. It goes without saying that the pieces of glass can only be trimmed and not cut along arbitrary lines: the glazier, however, can achieve the former much better and more safely with a tool that is common in his workshop, namely the cracking iron.
Recently, however, I received a pair of scissors from Paris which are excellently suited for trimming table glass, free in the hand without the aid of water. After my various experiments, all commonly occurring types of window glass, from the thinnest to handle the thickest, so lightly, conveniently, quickly, and safely that it is more of a game than a work. For longer straight cuts, the diamond is always preferred; indeed he maintains an exclusive applicability when dividing the tables, where both separate parts must remain intact. Just to cut corners, like to represent round and oval plates, etc., or even to adjust the edge of the glass to outwardly curved outlines, I can highly recommend the mentioned scissors from experience. It produces a cut edge of such good fine and blunt-jagged quality that it can remain in most cases (e.g. when the glass is placed in a frame) without further adjustment; If necessary, however, it is sufficiently smoothed by very slight regrinding on a sandstone. The superfluous pieces of glass that have been cut off shatter, but there is almost never the slightest disgusting crack towards the inside of the glass surface; and the trimming goes on almost as quickly as if one had a thin sheet of brass in one's hands. The small roughness of the edge can be almost completely removed afterwards by means of the scissors, by using them in such a way that they almost only remove dust. With the cracking iron, you work neither as cleanly nor as quickly. One only has to make sure that the scissors are always opened very little and that every pressure is little pushed forward; the opening and closing movements, however, may follow one another as swiftly as the hand is at all able to produce them. It is unnecessary to remark that - if one does not want to trust a sense of proportion but rather to follow a prescribed crooked line - the best thing to do is to temporarily glue a properly formed sheet of paper to the glass.
Now to the description of the scissors: the same looks like a hand-held tin snips in general, but is equipped with large oval rings for inserting the hands. On my specimen the total length, from the tip of the leaves to the end of the rings, is 11 1/4 inches (hannov.); of that, 2 3/4 inches is the distance between the tip and the center of the rivet. The opening of each ring measures 3 5/8 inches in length and 1 3/8 inches in width. The length of the cutting edges is 2 1/8 inches. - The most important peculiarity of these glass scissors lies in the sharpening of the cutting edges. The blades, which are almost a quarter of an inch thick, are ground a little hollow on the inner surface like other scissors, are sharpened from the outside by a single flat facet 5/16 inch wide so that the edge angle at the cutting edges is very close to 45 ° . This is a very significant deviation from tin snips, which have a similar wide and inclined facet, but whose cutting edges are broken by grinding a second, very narrow facet in such a way that the actual cutting angle is approximately 80 ° .
Since when the glass is cut, it is grasped between two thin, sharp cutting edges, pressure is created only on the narrow lines touched by the same, and the breaking off or breaking off of the glass particles occurs with as little action as possible on the parts of the surface lying next to them, which is why also no tension that could create an improper jump.
Very good hardening of the shear blades is, as it goes without saying, an essential condition. With the present scissors, there seems to have been no, or at most only a very slight, decrease after hardening. As could hardly be expected otherwise, through continued use it received a number of extremely fine nicks (only recognizable on closer inspection) in the cutting edges; this | 234 | but do not harm their effect. If, however, a weak burr should be erected sideways on the cutting edges, it would have to be rubbed off with a fine hand whetstone, just as the scissors must be properly maintained if they are to serve their purpose sufficiently. The price of these glass scissors is 15 francs in Paris. (Communications from the Hanover Trade Association, 1855, issue 1.)
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