By reviewing the action of the fly press, it will be interesting to see how the work accumulated in a moving body is applied to overcome the resistance offered when punching holes in metal plates. In this machine, fig. 282, a screw S of rapid pitch is attached to the fly lever F, which terminates at two massive cast-iron balls B, Bl, and on the lever is welded a rod E ending in a handle H. The operator exerts a certain pull-"quantity unknown"-upon the handle, which transmits motion to the fly lever F, and gives considerable velocity-"quantity unknown"-to the two balls, thereby causing work to be accumulated, this energy being available when required to punch the metal M.

"When calculating the work that can be performed in a fly press, neither the pitch of the screw, the length of the lever, or the pull applied at the handle are considered in the question."The screw is made of rapid pitch for several reasons, the two principal being-First, to enable the operator to raise or lower the punch P quickly by a small movement of the handle H, thereby allowing the various thicknesses of metal plate, or depth of articles, to be placed between the tools; also enabling the punch P to be raised up to the stripper S, F, without necessitating much movement of the operator. Second, the rapid pitch of screw assists the operator in giving velocity to the hills, and at same time the velocity is maintained. The effect of the descending weights of the balls is, however, disregarded when calculating the power of the fly press.

The work available for overcoming the resistance offered by the metal plate is that which is accumulated in the heavy balls B, B1 at the moment of impact. Let the resistance of the plate (which is supposed to be a constant or uniform resistance throughout its whole thickness), be denoted by R, let W be the combined weight of the two balls, v the velocity of the balls at the moment of impact, and let y feet equal the distance through which the resistance is overcome-i.e., y feet equal the thickness of metal plate. The accumulated work in the balls

=Wv2/2q also the work of the resistance = Ry, and by the principle of work

Wv2/2g = Ry; therefore

R = Wv2/2gy

Example.-Two balls, each weighing 301b., are placed at the ends of a horizontal fly lever 3 ft. long from centre to centre of the balls The lever imparts motion to a vertical screw of 2 in. pitch. What resistance will the punch overcome, if the balls have a velocity of 30 ft. per second at the moment of impact, and the punch is brought to rest after traversing a distance of 1/12th of an inch; also what energy is stored up in the balls. • Accumulated work or energy in balls

This 372.67 foot-pounds will be absorbed in punching the 1/12th inch plate, or through a space of 1/12 x 1/12= 1/144th of 1 ft.: therefore

. 53664.59 lb. is the mean resistance to the punch, when brought to rest in a space of 1/12th of an inch.

Fly Press Compared with Copying Press, Now let us see why the massive cast-iron balls are used upon the fly lever of a screw press. In the case of the copying press a certain pressure is applied to the letter book-so long as the hands are exerting the pull and the push-by working with a comparatively fine-pitch screw and a lever worked by both hands, and, where this lever has to be moved through the circumference of the circle described by P, several revolutions before the actual pressure is applied to the letter book; whereas the fly press has to be worked under entirely different conditions. The screw must necessarily be of rapid pitch, so that by the slight movement of the fly-lever handle, which is grasped by the operator's one hand, the punch may be quickly raised or lowered, leaving the operator's left-hand free to feed the metal articles on to the tools.

Suppose, for example, that the fly press, fig. 282, has a lever haudle H, upon which the operator exerts a pull of 501b., the radius of circle described by the handle H is 15 in., and the pitch of the screw is 2 in. Find the pressure applied at the punch P.

Here the pressure =50 x 2 π r / 2 = 2356.2 lb. In cutting-out or punching blanks, raising, drawing, and similar work in the fly press, the distance y feet through which the resistance is offered varies considerably, and the nature of this resistance is such that a continual pressure is required at the punch during the whole time that the work is being performed. The pressure of 2356.2 lb. which has been found by calculation, though useful for copying letters, would be absolutely useless in the fly press for punching holes through metal plate-unless the work was indeed very light Further, an operator could not exert a pull of 50 lb. at the lever handle H for very long, without becoming thoroughly exhausted, thereby loosing all his available energy, probably over cutting one thin blank.

Suppose the fly press is punching holes 1 in. diameter through a steel plate 1/8 in. thickness. By the shearing and punching formula we have

P = DxTxπxC; P = 1 x .125 x 3.1416 x 26.7 = 10.485 tons = 23486.4 lb.

Here is therefore a resistance of 23486.4 1b. offered by the steel plate whilst the 1 in. hole is being punched, and the screw-press calculation only resulted in a pressure of 2356.2 lb. Now, placing two balls upon the fly lever, each ball weighing 30 lb., considerably alters the conditions. The operator pushes the fly handle as far back as possible; then, when he comes to pull the handle H, the velocity attained by his hand is very great, and at the moment or instant of impact the operator throws the upper portion of his body back by a quick movement, thereby considerably increasing the velocity of the balls. The screw and the lever have greatly assisted him to attain the high velocity, but the energy given out by him has been accumulated in the balls, which in the previous example works out at 5366459 lb. at the punch, when the velocity was assumed to be 20 ft. per second.

Fig. 282.

By adding to the fly press the two cast-iron balls, the accumulated work is 372.67 foot-pounds, which enables the fly press to overcome a resistance of 53664.59 lb. at the punch.

The fact of adding the balls has made available over double the energy that is actually required to deal with the work the machine has in hand.

The great value of the stamp was mentioned in a previous article, and attention was drawn to its simplicity and cheapness as a means of storing energy, which could be given out again in doing the work of raising, stamping, and forging.