The Imperial Press. Dr. Lardner thus describes this press: — In this beautiful and compact machine, the works upon which the power depends are almost wholly concealed within the head of the press, and are in themselves extremely few and simple. The leverage connected with the bar is similar in principle to that of the Stanhope press; and the distinguishing peculiarity of this press consists in the manner in which the lever, called the chill, is made to act upon the piston, as represented in the engraving of the working parts.
The stout cast-iron lever or chill terminates in a sort of polished toe or point. This last-mentioned projection of the lever is made to act on a cup or knuckle acting upon the head of a stout iron bolt, which simply drops down a perforation of the piston, so as to rest upon the uppermost of two steel wedges, one of which, by its connexion with a screw in the front, admits of being pushed forward or drawn back, so as to elevate or lower the bolt, and thus regulate, by altering the length of the piston, the bearing of the platen upon the types. The head-bolt passes through a hole perforated somewhat obliquely; by which ingenious contrivance, a side twist, which would otherwise be occasioned by the motion of the head gear is avoided. It will now easily be perceived how, by the operation of the bar, the toe is made to act upon the inside bolt, and thus force down the piston, which, after the impression has been taken, is carried back again, by means of two stout steel springs attached to the insides of the cheeks of the press, and thus on the return of the bar lift the platen from the face of the types and allow the carriage with the form to be run out. These springs, operating uniformly, cause the action of the piston to be very smooth. The Imperial press, is, I believe, in high estimation for easiness in the pull, which gives it speed in working, and for evenness of impression.
On the first introduction of this press the toe of the lever or chill worked on a flat surface on the top of the bolt; the introduction of the cup or knuckle is a subsequent improvement.
They are made of different sizes, from foolscap folio to double royal.