The Quest for the Perfect Print!
The Setting of Platen
By Fred Williams
Editor-Publisher, Type & Press
Amateur printer Joe Novice is frustrated and cussing a blue steak. He has had his composition rollers recast, leveled his platen, makeready by "the book," using mint foundry type and a compatible ink/paper. But the resultant print is a disaster. Parts of the print are over inked while other parts refuse to print. Where did Joe go wrong? Possibly it could be that his rollers are incorrectly set.
First, consider the movement of the ink rollers on a typical platen press. Composition rollers are soft cylinderical surfaces cast from animal glue, molasses, wax, glycerine, vinegar, etc. Attached to steel shafts (cores) they are held in place with hooks (saddles) fastened over each end. These hooks are kept taught by springs which exert a constant tension on the cores to hold the rollers firmly against the printing surface. The roller trucks (wheels, gudgeons, trunnions) are round metal bearings and one is slipped on to each end of a core. These shafts have pins which engage slots in the trucks to keep the rollers turning.
Starting about one-quarter from the top of the ink disc, the trucks, riding on two rails, turn the inking rollers over the ink plate and down over the type form, depositing just a thin, even film of ink. The inkers make two passes over the type between each impression.
Rubber or synthetic rollers offer a number of advantages such as: (1) They are tough and resist damage or flattening. (2) They are little affected by changes in temperature or humidity and retain their original diameters. (3) They do not melt from ordinary heat or harden when cold. (4) They do not attract insects or rodents.
But because of their natural affinity for ink, compos transfer ink better than other rollers, therefore are still popular with Letterpressmen. They are tacky and exert a strong surface suction. Additionally they are reasonably priced and may be recast when their condition deteriorates.
Composition rollers are hygroscopic-meaning they are affected by too much or too little moisture in the air and by the temperature. They may shrink in size with decreasing humidity and swell when it increases. They may harden when the temperature drops and soften when it goes up. Excessive moisture will prevent the transfer of ink to the type form. Frictional heat or high temperatures may cause them to melt.
ComPos may swell so much they rub against each other and/or skid as they pass over the type. They may shrink so much that they fail to touch the type form.
If there is too much of a difference between the diameter of the trucks and the ink rollers, the two cannot roll in unison as they revolve over the type form.
Even if the trucks and rollers are the same diameter the rollers will persist in skidding if the roller tracks are worn.
Most presses, when new, have roller tracks that are type high (.918) above the bed. But after many years of destructive service the tracks may be worn down as much as six points–or more!
The ideal relationship is to have the roller just a tad bigger than the trucks. But no more than 1/16-inch. This will allow the type to drive the rollers so they do not skid on the type.
Swollen, moisture laden rollers, being larger than the trucks will hit the typeform hard and wipe away the ink instead of depositing it. This will damage the soft rollers as they contact sharp elements in the form. Damp rollers may repel the ink and an excessive amount may be required to get the form to print.
Shrunken rollers may have low spots. To get all parts of the form to print extra ink will have to be carried, resulting in excessive inking which causes offsetting. The tip off to this condition is a type form which prints O.K. when press is turned over slowly while making ready but goes light in spots just after run begins. You can see the impression of the type on the paper–but no ink on the form.
Achieving correct pressures on composition rollers presents a reappearing problem on a platen press. Fine printing demands that the rollers just lightly "kiss" the type with sufficient pressure to obtain full color without driving ink down into the counters or body of the type.
Because of this constant change in roller size some simple method is needed to check the diameters and some means to adjust the rollers and the type form so they will be the correct distance apart.
A few presses such as the Heidelberg and later models of some C&Ps came equipped with roller tracks having adjustable screws to solve this problem.
For presses without this feature, Expansion Roller Trucks* may be installed easily on most Gordon and similar open presses and will simplify -the adjustment of rollers. These "expanders" replace the regular trucks, fitting snuggly over roller core keys. They are equipped with rubber tires, which may be expanded or contracted to the required roller diameter by turning a locking nut.
But if adjustable trucks are not available, a number of temporary adjustments can made to raise or lower the inking rollers to their proper heigths.
To raise the rollers off the typeforms, strips of cardboard or leads may be cut and attached to the roller tracks. Or cellulose, medical or electricians' tape can be wound around the trucks which will increase their diameter.
Shrunken rollers can be brought into contact with the type by underlaying the entire form. That is by placing a sheet or two of oiled tympan paper or in extreme cases, a piece of thin sheet metal between the bottom of the type form and the bed of the press.
Check the diameter of the rollers daily with an accurate caliper. In lieu of one, wrap a piece of string around the inkers to determine the circumference. The diameter then can be computed.
There are a number of methods to check the pressure of the rollers on the type. The Paper Strip and Ink Band check, are two of the simplest ones.
Strip Method – Cut two Strips of 20 lb. paper 2 inches wide and one strip one-inch wide. Sandwich the small strip between the two wide ones and insert all three between one end of a roller and the type form. Then grasp the small strip and pull it out. If it slips out too easily, pressure is insufficient and roller diameter should be decreased. Remove any tape from the trucks or place material behind the typeform.
If the middle strip refuses to come out, there is too much pressure and tape should be wrapped around the trucks or material attached to the tracks. If only a firm tug is required to dislodge the center strip, pressure is correct. Cheek both ends of all rollers.
Ink Band Method –This test involves measuring the width of a band of ink produced by each roller at rest.
This cheek can be easily made if one has a roller gauge. This tool consists of a short section of round rod with a diameter of type high (.918) and mounted on an 8- to 12inch handle. To cheek rollers, hold the gauge by the handle and insert the head between the inked roller and the press bed. The ink smear left on the rod will determine the height of the rollers. Rollers then can be adjusted until they make the correct bandwidth on the gauge. The band should be identical on all rollers at both ends.
If a roller gauge is not available, the test can be made by holding a 60 point or larger type character face down on the bed of the press. Without moving the press, lift one end of a roller truck and slip the type beneath the roller. Carefully place the truck on the track fora moment then lift it back up. Remove type and measure the band of ink on the base of the piece of type. Repeat this test on each end of each roller.
The correct band of ink is determined by the diameter of the rollers.
Roughly if the roller has a diameter up to 2 1/2", the band should measure between 1/8" to 3/16". If the rollers caliper larger than 2 1/2" the ink band should measure uniformly from 1/4" to 5/16," wide. An ink band measuring outside these limits denotes too much or insufficient roller pressure.
A more precise way to determine the correct width of an ink band the following formula may be used: 1/16 (d) equals W, where d is roller diameter in inches and W is the correct band width. The width of the band should measure 1/16"" for every inch of roller diameter.