The principal reason why the roller-feed finds more favour and is so frequently adopted by sheet metal workers in preference to other feeding devices is on account of it being the only type of feed that can deal satisfactorily with sheet metals of the thinner gauges. Such metals, when being handled or uncoiled by an operator, will buckle or break unless reasonable care is used in the handling. Further, the least obstacle will result in impeding its advancement, and care is necessary in dealing with a metal so delicate to manipulate. From this it follows that when a roller-feed is used the pressure of the rolls, with their length extending beyond the full width of the sheet, keeps the latter flat for a considerable distance before and behind the rolls; they also tend to keep the metal stiff by giving it additional support. The first essential of a good roller-feed is the uniformity of its intermittent progressive motion. When this is perfect, piercing and blanking can be done with precision at an exceedingly high rate of feed, two hundred to three hundred blanks per minute being a very common speed for small articles. It is only when a large quantity of any particular article is required that the roller-feed is adopted. For small lots it has little or no economical application on account of the time occupied by an operator in adjusting the tools with the feed rolls. But when a 50 or 60 feet coil of metal can be started and cut up entirely, and while this is being done the attendant can be fixing up a second coil in an adjacent press, it will be readily understood that the rate of production is greatly increased, and the cost considerably reduced.

Fig. 185.

As a rule, feed-rolls (especially if they are double) will be in the way when tools are being re-set. It is therefore desirable that their construction be such as to make it possible for them to be readily removed for the purpose of tool-setting. This is effectively accomplished in the arrangement of the roller-feed, as shown in fig. 185, in which the feed rollers are hinged out of the way, the bed of the press being quite clear for setting the tools. The advantage in using a double set of feed-rollers is that whilst the front pair advance the sheet over the tools, the second pair serve to take the scrap or perforated sheet away and to deliver the last remnant of the sheet between the tools. Another important feature is that both pairs of feed-rollers should be capable of simultaneous opening, so that the metal sheet between them can be readily liberated and adjusted in relation to the tools and their gauges. This is accomplished by means of an eccentric lifter, thereby saving time.

The gear should be accurate machine-cut, and the crank-pin used to give motion to the rollers should be provided with a fine screw adjustment, so that the correct amount of advance can be given to the rolls. There is also usually added a device for automatically coiling up the scrap strip as it comes from the press. Small presses of this kind are especially suitable for making the covers of safety pins, glove fasteners, buttons, stud coverings, chain-links, small cups, and other similar small articles, of which a number may go together and be assembled to build up larger articles. In brief, it may be noted that for thin sheet-metal there is no feed-motion which gives better general results than the roller-feed motion when properly constructed. For thicker metals that will stand some degree of thrust without ready deflection, particularly if in narrow strips, the device known as the grip-feed, or monkey-feed, claims its place, whilst with wider metal the greater the claim of the roller-feed.

Fig. 186.

The purpose of the dial-feed motion is twofold. Firstly, and most important, it is a device that reduces the risk to a minimum of feeding or the laying under of the work. The great number of accidents in the way of operators' fingers being continually mutilated, would be materially reduced, if not altogether avoided, were the dial and other feed-motions more generally adopted. The second advantage is that the operator can feed the work at an exceedingly quick rate. The chief drawback to the use of the dial-feed motion is its cost, especially when applied to small quantities of work. Fig. 186 shows the dial-feed motion fitted to a power press.

Fig. 188.

Fig. 187.

The function of the dial-feed is to transfer the work from the hand that feeds it, into the tools that are used to pierce, bend, or reduce the article. Dial-feed motions are made in various forms; the one shown at figs. 187 to 191, is arranged for cupping-blanks that have been previously cut out on another machine. It usually consists of two circular plates about 12 in. diameter, the top plate T P having any number of holes an equal distance apart; the under plate B P is a fixture and has one hole only, this being exactly over that in the lower tool bed or die; this second or bottom plate B P forms a bottom or lower portion to all the holes in the top plate, see fig. 189. The t<>p plate T P is caused to rotate intermitently in one direction by a crank motion, usually on the end of the main shaft of the press, fig. 188, where it is shown in side elevation. A section of the crank motion showing the screw adjustment is also given at fig. 186. The advance of the plate T P occurs only during the upper half of the ascent and descent of the punch and during the lower half the upper plate holds the work to be cupped, drawn, or pierced, over the lower tool bed or die, while the punch descends and does its work. As the crank disc C D rotates, it gives motion to the connecting rod C R, which in turn transmits motion through the bell-crank lever B C L to the feeding-rod F R. On the rod is fixed a pawl P1, and this pawl moves the top dial-plate forward in its revolution, the small spring S keeps the pawl pressed up against the notches in the dial-plate. The function of the locking pawl L P, fig. 190, is to keep the top dial-plate steady in position. The blanks are placed in the cast-iron tray and pushed forward into that hole nearest the centre of the tray-each time the dial-plate comes to rest-they are then carried towards the tools as the dial-plate travels round in its revolution. By this arrangement the hands of the operator never need go near the tools. A rear elevation of the locking pawl is seen at fig. 191. The usual speed of the machine is from 100 to 130 revolutions per minute. Fig. 186, is the kind of press generally employed for making brass balls, knobs, cups, boxes, lamp burners, cartridge cases, and for accurately piercing any kind of blanks. The smaller the size of the work, the greater is the speed desirable, and in consequence the greater the risk to the fingers of the operator.