To procure variable blows, the operation is as follows:—
Pressure upon the treadle connected to the lever which operates the upright rod communicates itself to the treadle that opens the clamps, and the hammer falls; a locking device (not shown in cut) keeps this treadle down, and on completion of the variable blows wanted, removal of the foot from the treadle disconnects the locking device, and the hammer goes up to its original position, and is there held by the clamps.
When the work is such that the operator requires an assistant, variable blows may be obtained by the use of the hand lever by this assistant.
A gentle pressure upon the treadle will allow the hammer to go down slowly, but it will stop and remain suspended at any point as soon as the pressure is removed. The hammer can also be arrested at any point on its way up, by bringing into action the hand lever, so that the next blow can be given from a state of rest at a less height than the collar is set for. The clamps in holding up the hammer keep the board from touching either roll, and prevent the same from being worn uneven when not in use.
The back roll is made adjustable to different thicknesses of lifting board, as are also the clamps.
Fig. 3052.
