A few important design principles are built into the inking system. Each of these helps to optimize the efficiency of the inking system for depositing an even film of ink across the entire plate image.
Length of ink train. The number of rollers and the diameter of the rollers affect the distance that the ink travels from the fountain to the plate. The length of the train serves two important purposes. First, the ink begins at the ductor roller as an uneven, thick layer of ink. As it moves through the system it becomes progressively thinner and more even. Second, the ink stored in the long ink train resists changes in ink film thickness, which could be brought on by two different sources. The ductor roller, which intermittently replenishes ink to the train, produces surges in ink thickness to rollers early in the system. The long ink train acts as a buffer to combat this surge of ink. Also, ink is constantly being drawn from the ink system by the plate, but in varying amounts. The length of the ink train assures that ink will be replenished to the form rollers as an even ink film.
Variations in roller diameters. The rollers in the inking system vary in diameter, with rider rollers having the smallest diameter and oscillators the largest. Because the diameters vary, the RPMs (revolutions per minute) of the rollers vary as well. This design principle helps eliminate repeat flaws. This can be understood by considering a series of rollers that have the same diameter, any flaw in the ink film would transfer from one roller to the next, moving throughout the system to the plate. The diameter variations, coupled with roller oscillation, eliminate any repeat flaws.
Alternation of hard and soft rollers. Rollers in the ink train generally alternate between hard nylon or copperplated steel rollers and soft, synthetic rubber rollers. This allows precise pressures to be set between rollers, with the soft rollers able to pivot on journals against the hard, stationary rollers. Accurately setting the pressures between rollers is critical, as it affects the even transfer of ink throughout the system.