Setting the Register Rack
For perfect register it is essential that the impression cylinder should, from commencement to finish of printing, operate in complete harmony with the type bed, irrespective of possible disturbing factors such as backlash or play in the gears, the fall of the cylinder, etc. In effect the grip edges of the cylinder must be brought into correct relationship with the type bed, prior to commencement of printing, by positive means. This is achieved by means of the short segment and rack with which the cylinder and type bed are fitted.
The leading teeth of the segment rack are relieved in varying degree. This ensures, as the gear and rack run into mesh, that the engagement is gradually and smoothly brought about. The remaining teeth are of standard size and thickness. Before the cylinder is hard down on the type bearers, the rack should have performed its function, and prior to this the tapered ends of the type bed bearers in conjunction with the leading teeth of the segment rack enable the pressure of the cylinder to be taken up gradually and without shock.
A broad slur across the front edge of the impression cylinder will indicate the leading edge of the register rack is worn. (When machine is on printing stroke, the upper traverse rack is engaged.)
1. With the cylinder tripped for impression, turn the press over until the type bed register rack comes into mesh centrally with the first three teeth on the cylinder segment rack and then