The anvils are suitably supported from moving rearwardly at the bottom by toggle mechanism between the back of each anvil near the bottom thereof and a stationary bearing supported by the frame structure.Each toggle is normally a little off dead center with the central members of the toggles strongly pressed resiliently toward their dead center positions,gold mining machines whereby the crushing force applied to the front of either anvil if sufficient to cause any bending of its toggle must overcome an adjustably heavy retraction of a spring tending to straighten the toggle.
Until the force on the spring is relatively great, the toggle will maintain its position, but as soon as the spring begins to yield, further yielding will be quick and easy, as the proportion of the total force transmitted to the spring rapidly increases as the toggle bends, so that there is no yielding of the toggle unless or until the pressure upon the front of the anvil is to a predetermined extent above normal, when the toggle snaps into release to automatically reset under the action of the spring as soon as the rocker retracts, permitting the uncrushable object to pass downward from between the jaws.
As shown each toggle comprises an intermediate head 75' and toggle arms 76' and 77' along opposite sides of the head and respectively engaging at their other ends the back of the anvil and a stationary bearing. The ends of the toggle arms form convex rib-like pivots, as shown at 88, for example. The head 75' is provided with flat seats 78' at intervals along its upper side and is vertically bored and threaded at the middle of each seat to attach the lower ends of bolts 79.