Rubber Hand Stamps and the Manipulation of Rubber / A practical treatise on the manufacture of India rubber hand stamps, small articles of India rubber, the hektograph, special inks, cements, and allied subjects

by T. O'Conor Sloane

Simple Vulcanizing Press for Rubber Stamps.

The first thing to be described is the mould, which includes the arrangements for pressing the sheet of india rubber while heated. A small press is needed for this purpose. It may be of the simplest description, and as an example of a home-made but perfectly efficient one the illustration may be referred to. The base of the press is a piece of iron, if heat is to be directly employed. Where a chamber vulcanizer is used both base and platen may be of wood. But from every point of view iron is the best. It lasts forever, admits of direct heating, and does not split, warp, or char. Through two holes drilled near its opposite sides two ordinary bolts are thrust. It is best to use flat headed bolts, and to countersink a recess for the heads in order to keep the bottom level. The heads may need to be filed off so as to reduce their thickness, in order to secure this object. The bolts may be soldered in place. One thing should be carefully watched for—the bolts should be set true so as to rise vertically from the plane of the base.

The platen is best made of iron, cut of the shape shown. This is an excellent disposition of the screw-bolt slots, as by swinging the right end of the platen back it can be taken off without removing the nuts and lifting it over the ends of the screws. Besides the two nuts fitting the thread of the screws it is well to have half a dozen extra ones larger than the others, which will slip easily over the bolts, so as to act as washers. The object of these is to adapt the press to objects of different thickness. The thread upon an ordinary bolt does not extend clear to the head, but by slipping on some loose nuts the plates can be forced together if desired.

This press can be simplified. Both base and platen can be made of wood, the platen being simply bored for the bolts, and the latter driven tightly through the holes in the base so as to retain their place. Even this can be improved on as regards simplicity. Two blocks of wood screwed together by two or more long wood screws may be made to do efficient work.

One trouble is apparent with all these devices, and that is the want of parallelism of the opposed planes. The base and platen may be true and parallel or they may not. Perhaps the simplest way of securing this is the best. It consists in placing across the base two distance pieces, which may be slips of wood. These must have perfectly parallel faces. As the press is screwed up they will be gripped between the platen and base and will not only ensure their parallelism but will keep them at an exact distance apart. Such distance pieces are shown in the same cut. Pieces of printers’ “furniture,” spaces, or “quads,” may be used for this purpose. They should not be fastened in place if there is need to adapt the press to more than one thickness of material and matrix.

The above described apparatus is a vulcanizing press. A further improvement in it may be effected by the use of spring pressure. Two strong spiral springs may be dropped over the bolts, the nuts being screwed on above them, or a powerful spring of flat brass or steel ribband bent into the shape of a shallow letter V may intervene between nuts and platen, the centre of the bend bearing against the centre of the platen.

As regards the strength of the springs there is this to be said. The distance pieces will prevent a spring that would ordinarily be too powerful from doing any harm. Such distance pieces should be used, as the springs must be based upon giving a pressure of many pounds per square inch of surface to be acted on. They should have a range of an eighth of an inch or more. The greater the range the more evenly will they work.

The next [cut] shows an excellent little screw press, that is made for the purpose of pressing vulcanizing flasks. This is so simple that it will suggest to the mechanical reader how he can make a single-screw press, which is by far the most convenient to use. In the stationery stores very small model cast iron copying presses designed for use as paper weights are sold. They are excellent for a limited amount of small sized work.