A difficulty often experienced with double-crank presses, is the adjustment of the two connecting-rods, so as to ensure that the punch or top die (as the case may be) will come down on to the bottom die and be perfectly level. This is very important when a press has to be used on a variety of work requiring connecting-rod adjustments. A worm adjustment is used in connection with some double-crank power-presses, and has the advantage that it enables the adjusting links to be securely locked at the top and bottom. In many makes of presses, particularly those of American design, there is no proper means of locking these adjusting links or couplings, and the adjustment is therefore liable to be altered during the working of the press. One tpye of worm adjustment is seen at fig. 201, fitted to a cutting-out, stamping, and embossing press, capable of exerting a working pressure on the dies up to 100 tons.

Fig. 201

Fig. 202.

Fig. 203.

There are instances, where a small adjustment only is necessary to meet the slight variation in setting the tools; such a press as is shown in fig. 202, where a pair of wheels are attached, one of which is provided with an eccentric brass-bush, and by this means an adjustment of 1 in. is provided. Such a machine is suitable for cutting out heavy blanks in sheet iron and steel-for armature discs, blanks for bottoms of buckets, baths, and similar work, and is fitted with a treadle motion, by means of which the ram makes one descent and stops automatically at the highest point.

A geared press of somewhat similar design is usually employed for such work as pannelling or embossing trunk bodies and covers, by means of dies, a class of work that has usually been done by means of a hand-swaging machine with rollers.

A geared machine known as a toggle drawing press is shown at fig. 203 with its slides up. This tpye of press is employed upon all kinds of seamless articles, such as basins and other kitchen utensils. The special toggle movement is provided for application to the blank holder, and by this mechanism the pressure put upon the blank under operation is borne by the framework of the machine, thereby reducing the strain and friction upon the crank shaft.

A perforating machine suitable for dealing with heavy sheets and fitted up with automatic feed-table to ensure accurate work is also made. The machine may be employed for punching heavy blanks from the sheet, and which, owing to the machine being automatic, enables the work to be done rapidly and permits one operator attending to two or three machines. It is fitted with hand-lever clutch, by which means the operator can stop the machine instantly if required.

Fig. 204.

Fig. 205.

The armature disc-notching machine, fig. 204, is a type of machine specially built for the electrical trades. It will be noticed that the machine consists of an ordinary cutting press, fitted to a suitable bed casting which is truly planed to receive the powerful automatic and adjustable stop mechanism which controls the action of the horizontal rotating movements, ensuring thereby uniformity in the discs that are notched in the press. A positive clutch is provided by means of which punching is automatically stopped after one complete revolution of the disc under operation.

In some instances, as in the case of chamfering, marking, piercing, and burnishing cycle chain links, and similar blanks, it is convenient to pass the blanks on to the tools automatically. Fig. 205 shows a press fitted up for this purpose. Vertical hoppers or tubes of suitable size are provided to receive the blanks, and from these tubes the blanks are automatically conveyed to the dies to be chamfered, marked, or pierced, and after being operated upon fall through the bed into a box placed for their reception.