Good-bye to Misfeeds With a
By Fred Williams
Editor-Publisher, Type & Press
Published Summer 1984
Any platen press equipped with a mechanical feeder, properly adjusted & manned by an experienced pressman, is a marvel as it clanks along hour after hour, with scarcely a misfeed –depositing each sheet gently right up to the gauge pins. But the average novice, hand feeding, will after a few hundred impressions, become bored and will likely become careless in the placing of the sheets on the platen. But if each sheet is not placed in the exactly the same position and held there while the type "bites" into the paper, the job will be out of register.
A print job is said to "register" when each impression is made in exactly the same spot on every sheet. This is absolutely essential if equal margins are to be maintained and a must if the paper is to be run through the press more than once –to print more than one color or be perforated, embossed, numbered, die cut, creased, etc.
The accuracy of registration on a press can be checked by feeding about 15 or so sheets through the press, twice to the same gauge (or guide) pins. When the sheets are examined with a magnifying class they should reveal that every line and halftone dot has printed in exactly the same spot during both printings. If the result is a double image, the cause may be one or more of the following:
The most common causes of mis-register are: inaccurate feeding; movement of guides, form elements or chase; press not level, static electricity, changes in paper stock, variations in press speed or maladjustment of the grippers.
IS PRESS LEVEL?–Check by using a small carpenter's level on the shaft. If the press is low on the gear side the action of the cam may cause the sheets to jerk away from the end (side) guide. To remedy, raise right side until the shaft is level.
Old platens often have a jerky side action and some country shops had their platen presses set up with the gear side raised 1/8- to 1/4-inch higher than the flywheel side. Then any jerky cam action would cause the sheet to slide against the side guide pin rather than away from it.
INACCURATE FEEDING–Guides should be placed to facilitate easy feeding, the ones for the lower edge of the sheet, not too close to the corners. The end one should be placed about in the center of the sheet, up and down. Large sheets may require two side guides. Sheets to be printed should be fed first to the two bottom ones, about 1/2-inch from the side guide and then slid gently over to the side guide. Never should they be jabbed at all pins simultaneously. The paper should be placed lightly to the guides to prevent the sheet from springing back or moving of the guides.
Even if the sheet has been placed lightly against guides, static electricity may cause the paper to cling to the pressman's hand as it is with drawn. Therefore, the fingers should be slightly twisted just before releasing the sheet to break this adherence.
The novice may fantasize that he wants to be a "speed merchant," dreaming of feeding 1800 or so sheets per hour. Forget it! Never run a press at a speed that is difficult to keep up with. A slow speed, allowing sufficient time for the careful placing of each sheet lightly against the guides will prevent getting rattled, overworking the throw-off and printing crooked on the paper. The finished print will speak for itself. No one cares how fast or how slow a job was fed. Strive for a good, even unfailing "motion' as that possessed by a competent hand compositor.
MOVING OF GUIDES–After print is positioned on top sheet, points of guides should be tapped down into tympan and anchored with a few drops of sealing wax that overlap guides and the top sheet. Candle wax can be substituted. Guides may move during run if secured only with Scotch tape. The repeated pressure of sheets being placed against them may cause guides to "walk" if not anchored.
If guide pin tongues are not correctly adjusted they may allow vertical play in the sheet, causing misregister. A small wooden wedge inserted on the top of the tongues will force them against the top sheet thereby eliminating up and down movement.
SHIFTING OF FORM ELEMENTS–If necessary to unlock form during the run, re-lock with exactly the same pressure. Before unlocking, mark quoins with chalk on opposite teeth (Hempels), key slot and case (Wickersham). Numbers on Hi Speeds denote points of expansion.
If guides or form elements move in any way duringthe first run of a multi-color job, nothing can be done to rectify it during succeeding runs. The job will have to be re-run. To keep a constant check, before starting a run, feed a set of trial sheets through the press and insert them into the unprinted lift at intervals of about every 100 or so sheets. In this way the pressman can be positive that registration is being maintained throughout the run by examining each trial sheet as it is printed. At the first sign of a misregister, corrective measures can be instituted.
PLAY IN CHASE–Horizontal play between the chases and roller tracks can be eliminated by sliding chase to the left and forcing a wooden wedge between the right end of the chase and the tracks.
PAPER CHANGES–Large sheets of paper may shrink or swell due to variations in the humidity. This can result in subsequent runs that won't register. Store paper in pressroom until allchanges take place prior to printing.
ADJUSTMENT OF GRIPPERS–If grippers or fingers are set too tight, they may move the sheet away from the guides. These striping devices must be sete so they will lay flat on the top sheet and "freeze" during the moment of impression.
VARIATION IN PRESS SPEED–Speeding up or slowing down the speed of the press during a run can affect registration. Try to maintain a uniform speed throughout the entire run.
But,if in spite of all these precautions, the paper fails to remain motionless during printing here is an old time pressman's "secret" that porbably will solve these problems. The use of a "Flying Dutchman" will prevent kicking, bouncing or movement of the sheet before, during and after impression. One can be used on any job—easily.
The "Dutchman," only requires the cutting of two small slits in the top sheet, opposite the side guide, along the right edge where the stock rests (See illustration below). Place a sheet of the stock to be printed tight up against all guides and cut along the right edge of the stock (A to B and B to C). The points (A and C) will be folded up about 1/8" above the top sheet. This will form a triangle tab about 1x1/4." Size is not important.
The Dutchman will depress as the unprinted sheet is set over it. When the paper is tight to the side guide, it will fly up and hold the sheet securely as the grippers close against the sheet. It will be impossible for sheet to move from guides.
The printed sheet can be removed from the tight clutch of the Dutchman by grasping it in its center and pulling straight out.