Fig. 162.

A type of press called single-acting is shown at fig. 163, this pattern being used extensively. It3 chief defect is the form of stop motion, that tends to stop the motion of the slide the moment the operator's foot is taken off the treadle. This is sometimes with the slide up at, or near the top of its stroke, and at others with it down at, or near the bottom; and it frequently requires some considerable practice] on the part of the operator to get into the way of stopping the slide in the right place. Even when this type of press is operated by a competent attendant, it is subjected to the great knocking and hammering at the clutch, as was mentioned when figs. 43 and 44 were being described. This defect is, however, overcome by the substitution of the special stop motion, described and illustrated at fig. 172, which disengages and leaves the slide at the top of its stroke, and avoids the unpleasant shock. It is also much easier to work the treadle than when the ordinary clutch is used, as with the special stop motion, fig. 172, there is little or no shock to the foot of the operator; whereas, with the claw-clutch stop motion, the operator feels an unpleasant jerk or shock each time the press is started

Fig. 163.

The single-acting press has its chief application in light work, or that of medium strength, say up to 14 B.W.G. in iron or steel, and to about 10 B.W.G. in brass, and even thicker in copper. But when any of these metals exceed the thicknesses here mentioned, then a geared press is to be preferred, for the reason that more time is allowed to do the actual cutting, and the press is saved those sudden jerky strains that so frequently break the main casting or the end of the crank shaft. In the steel trades the number of breakdowns that arise from this one cause is notorious, especially when cutting thick steel, and it is of a hard nature, and sheared cold; whereas a geared press of the same strength would do the same, if not heavier and harder work, with less strain, all because the work is done gradually, and therefore with less shock.

In the case of heavy work in single-acting presses at a high velocity, the almost instantaneous manner by which it dashes the tool through the metal, or forces out the blank, is liable to break the main casting or shaft; and one of the functions of gearing should be the avoidance of this sudden imposition of great strain on the main casting. For cutting out hot work, or for bending, squeezing, and forging, the gearing is not so important, so long as the thickness is not too great. All forging and squeezing should be done as rapidly as possible, as in the Ryder forging machine, for which the single-acting press is a cheap substitute.

The single-acting open-back upright press, shown at fig. 164, is of the long-slide series, having long slides and guides. it is, therefore, best suited to work requiring a long stroke. The connecting rod has screw adjustment, and at the base of the rod there is a wedge adjustment to take up future wear. There is a loose gland or cap on the base of the slide, handy for the ready removal of the punch or top tool, without removing or even disturbing the bottom tool or die. The many advantages of this arrangement will be apparent to those who have had experience in press-tool setting. Fig. 164 also shows a loose bedplate, that can be removed or replaced with others of various thicknesses or styles to meet great ranges or varieties of work. It will also be seen that a rod is placed in one of the holes of the bottom nut of the connecting-rod adjustment, ready to raise or lower the slide. A press of similar construction is shown at fig. 165, with the exception that this press is geared with helical wheel and pinion.

Fig. 164.

In fig. 165 it will be noticed that a rod is placed in a hole of a cast-iron disc. This disc serves the double purpose of assisting the tool-setter by enabling him to raise or lower the slide by means of the rod, and the disc having one point in its circumference standing higher than any other, this high 12wp point comes against a piece of hard wood, thereby acting as a brake to stop the press bolt or slide when it has reached the top of its stroke.

The cutting-out and raising press, fig. 166, is of an older design than fig. 167. In the case of the design, fig. 166, there are the usual cams on either side of the crank operating on hardened steel rollers carried by crossbars, which are secured to the square frame. Over the cams are another pair of rollers connected to the upper part of the same frame. This gives a positive lift to the pressure plate; this is of importance when the pressure plate is required to carry a cutting-out tool-that is, to cut out and then immediately secure its blank and prevent wrinkles forming whilst the forcer punch sends it into the die. The springs shown are for the purpose of balancing the pressure-plate framings.

Fig. 165.

In the case of a drawing press being used for cutting out the blank previous to drawing or raising it into some deep-formed article, it is much better for the pressure plate to have a positive lift, because sometimes the top tool will jam or bind in the bed, or the metal may get between and cause it to bind, and then the springs by themselves (see fig. 166) would not lift it out, on account of the springs not being sufficiently powerful.

Fig. 166.

There is another form of pressure plate used for drawing extra deep work. This type has a nozzle fitting inside the die which presses the work against the inside of the die, thereby keeping the wrinkles out of the metal whilst the drawing process is further continued. In this kind of work the positive lift to the pressure plate is very desirable.

In the case of feed rolls and feed motions being used in drawing presses, the positive lift to pressure plate is essential, because the work is usually cut and raised at the same time, so that in case the blanking tool was not lifted out of the metal, the rolls or feed motion could not work, and the resulting derangement would lead to waste of material, loss of time, and a necessity for entire re-adjustment.

The press, fig. 167, combines the advantage of a cutting-out, raising, and drawing press. The pressure plate descends by gravity until it rests on the lower die, then the continued descent of the forcer slide (by means of the central rollers) acting upon the incline expands the inverted toggles under the adjustable rollers, which are secured on to the side of the main frame of the machine. This transfers the pressure required to hold down the blank on to the main casting, and thereby relieves the crank of this duty, the crank having to only sustain the pressure of raising the blank.

Fig. 167.

Fig. 168 shows the change in the position of the parts when the crank is at the bottom of its stroke. There are toggles and adjustable rollers at the back and front of the slide, the pressure plate being held down at four points, the adjustments are positive, the effect being that the work done in this press would be of an exceedingly uniform quality. A press of this type, figs. 167 and 168, would be specially suitable for such articles as lock-furniture knobs, bedstead knobs and mounts, chandelier weights, drinking cups, lamp bodies, cones, burners, fox The pressure plate may be removed from the press in a few moments, when the press immediately becomes available, either for cutting out blanks, drawing, extending, and reducing work (that has been previously raised by the aid of the pressure plate). This form of press, with the pressure plate removed, is shown at fig. 169. In presses of this type the crank and its load should be effectively balanced during descent. and this can be done by having a disc within the spur wheel, which is heaviest on the opposite side to the crank.

Fig. 168.

The double-crank, double-sided geared press, tig. 170, is a special design for cutting large blanks for baths, two or three thicknesses of metal being cut at one stroke. Such a press would l>e about six tons weight, and could pass a blank through its base measuring about 43 in. by 19 in. The slide has a vertical adjustment effected by eccentrics caused to rotate by a tangent screw projecting in front of the slide. This means of adjustment always keeps the base of the slide parallel with the bed or table of the press. The slide is also balanced, thereby preventing any tendency for the slide to overrun in its downward stroke, or unexpected falling of the slide due to its great weight. This feature of balancing the slides secures safety to the operator. The double-helical gearing is driven by a friction clutch, which is automatically disengaged as the press slide reaches the top of its stroke; pressure on the front treadle allows the clutch to engage and thereby stare the machine in motion. The speed of a large press, such as fig. 170, is usually about 30 strokes per minute, and the cutting-out tools would have waved cutting edges, giving shear to the tools, thereby enabling two or more complete bath bodies to be cut out at each stroke of the press.

Fig. 160.

Fig. 170.