In presses equipped with adjustable beds, the steel slab that is the bed of the flatbed cylinder press is connected to a wedge system that raises and lowers the bed of the press, with accuracy to a thousandth of an inch.
Benefits of an Adjustable Bed
An adjustable bed makes easy work of printing type on galleys (simply lower the bed to .968), or directly on the bed (.918), but it also allows for wood type and blocks that are far from type-height (either short or tall). It also facilitates the printing of non-American-height type, including Dutch (.978) and French (.933).
Where the bed comes in very handy is that a change in press sheet thickness doesn’t require changing packing: the difference in paper thickness can be adjusted by raising or lowering the bed (although if you’re changing paper, you’re probably also changing the printing surface [type or block], and thus it’s probably a good idea to change your packing anyway).
To set up a non-standard bed height, pack the cylinder to the standard depth (stamped on the cylinder on Vandercooks, normally .040), and set the rollers with the bed set to standard .918. Then lock up the non-.918 type or block, lower the bed past the printing surface threshold (after gauging the type or block with a micrometer to determine the height), and gradually raise the bed until an impression is achieved. Continue to raise the bed until the desired impression in the paper is achieved (without ink), then lower the rollers to begin printing. Because the roller height is set with the bed at standard .918, the contact between roller and printing surface will provide good ink transfer, because the bed has been set to position the printing surface relative to the roller and cylinder.
The height adjustment is a simple matter of releasing the locking bolt on the adjustment spindle, turning the spindle counter-clockwise to lower the bed, then turning it clockwise to raise it back to the desired height. It’s important to always lower the bed beyond your printing threshold and then raise it to the desired height in order to eliminate any play in the spindle/lever system.