The lithographic hand press
The flatbed hand press (sometimes called the hand transfer press) is the traditional machine for printing lithographs directly from stone and metal plates.
Hand presses of this type have not been manufactured or used commercially for the past fifty years. They were last used for commercial purposes in the transferring departments of the larger poster, decalcomania, and label printing establishments during the 1930s. With the rapid development of photo-reproduction techniques, motorized transfer presses, and highspeed offset presses, the slower hand presses were phased out of industrial use and often sold as scrap metal. A small number of presses were salvaged by schools and individual artists during the 1930s; many of these remain in excellent operating condition and perform dependably.
Today the discovery of old, unused hand presses is mostly a matter of luck, although a few may still exist in forgotten storage rooms of the older lithography firms. Despite their simple construction, they command exorbitant prices when they appear, infrequently, on the market. Until recently, the scarcity of these presses had been a serious detriment to the advancement of artistic lithography. Moreover, when damage occurred on existing presses, parts could not be replaced except through expcnsive custom fabrication. Fortunately, the current revival of interest in hand lithography has encouraged the manufacture of new presses, which will alleviate the shortage of adequate machinery.
Press construction and operating principles
The construction and operating principles of the traditional hand transfer press are essentially the same for all makes and sizes.
Two cast-iron frames are bolted together and held rigidly by cross bars at the front and back.
A cast arch is bolted between the uprights of the frame.
A screw that regulates pressure passes through the arch and is attached at its lower end to the scraper box. The screw is turned by a key or pin inserted through its top. This permits the regulation of pressure by raising or lowering the scraper box.
The scraper box is a heavy metal cross bar channeled along its underside for housing the scraper bar. A set screw for securing the scraper bar is positioned at the center point of the box. The box, free at each end, is self aligning to the stone when pressure is applied.
The scraper bar is a wooden blade with a beveled contour along its lower edge. A strip of leather is stretched tighly along this edge to serve as a resilient cushion when pressure is exerted between the scraper and the tympan sheet. The scraper is not a an integral part of the press.
The press bed (table) is constructed of heavy maple planks. A series of thin iron straps is screwed along the length of the bed on its underside to provide traction and to prevent frictional wear when the bed is moving. It is essential for the press bed to have a true plane without indentation or warp. A sheet of battleship linoleum is fastened on the upper side of the bed as a cushioning. Over this sheet, a thin sheet of zinc, aluminum, or galvanized metal is secured to provide a durable and easy-to-clean work surface. The long sides of the bed are protected by metal slides, which reduce friction as the bed moves within the rails of the press frame. Its movement is supported by a series of wheels called bed runners, which rotate in shafts that are an integral part of the frame.
The operating mechanism consists of three basic units : (a) the pressure lever, (b) the connecting rod and cams, and (c) the bed roller, gears, and handle.
- The pressure lever is a heavy steel rod connected to the cams. When the rod is lowered, it rotates the cams, thus raising the bed roller into contact with the press bed.
- The cams rest on bearing blocks which are seated in slots on the lower part of the frame uprights. The connecting rods rest on the cams, and the ends of the rods support the shaft of the bed roller. The bearing blocks are fitted with turn screws for adjusting the level of the bed roller and press bed.
- The bed roller is a steel cylinder of large diameter which carries the press bed forward and backward when the press is engaged. A turning handle, or crank, is attached on one end of the bed roller, and a gear train is attached on the other end. When the pressure lever is upright, the press is disengaged. In this position, the cams do not permit the bed roller to make contact with the press bed. This permits the bed to be pulled or pushed by hand along the bed runners. When the pressure lever is brought down, the actions of the cams and connecting rods raise the bed roller into contact with the bed.
Thus engaged, the bed may be cranked forward or backward by means of the handle and gears. The movement is produced by the friction of the bed roller turning against the metal strapping on the underside of the bed.Tympans were originally an integral part of the hand press; they consisted of an iron frame hinged to the leading edge of the bed. The frame was covered with a thin sheet of zinc or leather, lubricated on its top surface. The tympan frame was lowered over the printing stone and paper, serving as the bearing surface over which the scraper would glide when the press was in operation. This system was heavy and cumbersome, and was eventually replaced by simple, removable tympans that could be easily positioned by hand. These are no longer an integral part of the press.
