Fig. 1832.
Fig. 1833.
The connection between the die ring b and the clutch ring c is shown in [Figs. 1832] and [1833], the former being also a longitudinal sectional view of the head, but taken in a different plane from that in [Fig. 1830]. The barrel or body a a of the head is provided with two diametrically opposite curved rocking levers which are pivoted in recesses in a a. The clutch ring c envelops body a and passes between the curved ends of these rocking levers. The upper of the two rocker levers shown in the engraving connects with a lever e, which connects to a stud or plunger p, threaded to receive the adjusting screw i, which is threaded into the die ring b. Obviously when c is moved to the right along a it operates the rocking lever and causes b to move to the right and to close the dies upon the work. The amount of die closure, and therefore the diameter to which the dies will thread the work, is adjustable by means of the adjusting screw i, which has a coarse thread in b and a finer one in p, hence screwing up i draws b to the left and farther over the plunger p, thus shortening the distance between the centre of the curved lever and limiting the motion of b to the right. On the other hand, unscrewing i moves b to the right, and it is obvious that in doing this the cap t in [Fig. 1830] is forced down by the groove in b and the dies are moved endwise towards the axis a a, or in other words, closed.
It will be clear that a greater amount of power will be necessary to hold the dies to their cut than to release them from it, and on that account the lower curved rocking arm d connects through e to a solid plunger g, the screw h abutting against the end of g and not threading into it, because g is only operative in pushing b forward in conjunction with p, while p pulls b backward, the duty being light. It is obvious, however, that after the adjustment screw i is operated to set the dies to cut to the proper diameter, adjustment screw h must be operated to bring the ring b fair and true upon a a and prevent any lateral strain that might otherwise ensue.
These two adjustments being made the clutch ring c is operated to the left to its full limit of motion to open the dies and to its full limit to the right to close them.
It will be seen, by the lines that are marked to pass through the pivoting pins of the rocking lever d, that the joints marked 2 in [Fig. 1832] are below these lines, and as a result the links e form in effect a toggle joint locking firmer in proportion as the strain upon them is greater.