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Setting the tolerances on rollers, be it platens or cylinders, is not difficult, but requires considerable care and attention when quality printing is paramount. There are quite a few different roller gauges available, for example the micrometric setting gauge (complete with dial indicator), the block gauge, the free-wheeling roller, and the simple fixed wheel type, seen below, which is my preference. Diameter of the cylindrical reading head is .918", or 'type-high'.
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PLATENS
NON-ADJUSTABLE
As most platens do not have the rolling power to fully cover the depth of a forme, it is essential the rollers contribute equally. Therefore all should share a common diameter with the roller runners [trucks], be perfectly circular and the stocks [cores or spindles] aligned true. This can be checked by placing each roller, runners attached, on a perfectly flat surface - a steel imposing surface or lithographer's stone for example, and turning the roller over slowly. A light source behind the roller will highlight any difference between runner-to-roller height, out-of-round stocks or lop-sided coverings.
Assuming the bearers are in good condition and free from oil/dirt, place the rollers in their correct saddle positions and run up ink to about normal coverage. Platen settings require that readings must be taken from both top and bottom, unlike cylinder machines, as bearers can be worn unevenly, especially on the older machinery. Eyeball the bottom roller so it is level with the bottom of the bed (but not beyond!) or where the base of the chase would normally be. Now slide the roller gauge in from the top along the bed flat side up, and push down underneath all the rollers. When beyond the last, turn the roller gauge 90 degrees so the rounded surface is up and drag up under the bottom roller, to obtain a reading. There should be a slight drag. Now turn the gauge back 90 degrees so that the inked reading won't be disturbed when gauge is removed. (If all the rollers are exactly the same dimensions then there is theoretically no need to check the others, but it doesn't take much effort to 'double-check'). Measure the ink strip and record it. Clean off the previous stripe and repeat the procedure with the rollers moved to the top of the bed. Standard width for 'composition' is from 10 to 12 points, less for plastic, polyurethane or rubber compounds.
Remember to keep turning the gauge after each ink transfer to avoid a misread!
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ADJUSTABLE
Many later platens, both hand-fed and automatic, incorporated simple means for adjusting roller height and included screw, wedge and cam devices. Gauge setting is done in the same way as non-adjustable platens but much quicker! Remember, adjusting one end can adversely affect the setting of the other end and also the opposite bearer, so double-check readings after each adjustment.
BEARER ADJUSTMENTS ON OLDER TYPES
Usually these need building up on old hand platens, due to wear, tear and misuse. Unfortunately no means for mechanical adjustment were built into the older makes, which all (when new) had a fixed bearer height slightly less than type-high. This difference gave the inkers a slight touch to the forme which would equate to the recommended ink stripe. Strips of card or plastic can be attached with suitable adhesive and magnetic tapes have also been suggested but this 'stop-gap' method will not last long as the materials will be pulverised away eventually.
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A simple solution is to attach thin steel tapes over the bearers - packaging strapping is ideal - by drilling, thread tapping and inserting a small mushroom-headed bolt into the area beyond the limit of the bottom roller, threading the tape up and around the 'lead-in' and connecting to a small turnbuckle, the other end of which can be fixed similarly to the top or even at the back of the casting. This allows the straps to be loosened or tightened up without any movement and also accommodates packing and 'makeready' in between, if bearers are worn unevenly, enabling an exact roller to bed height.
CYLINDERS
All forme rollers on flat-bed cylinder machines are individually mounted in adjustable bearings and usually driven by a steel rider geared to the bed rack. Therefore accurate settings both roller-to-type and roller-to-rider can be attained and negates the need for all inkers to have a common diameter.
Gauge readings are taken in much the same way as platens, the only difference being inkers also have to be adjusted laterally to the steel rider roller. Both require to be set at the one time, as for example, lowering a forme roller to it's correct setting may disengage it from contact with the rider or vice-versa. Usually a minor height adjustment won't cause a problem with the lateral one, however, when replacing old rollers with new, it is advisable to proceed one roller at a time, starting with the one closest to the cylinder. Run up ink then allow the press to sit for 30 seconds or so. Inching the press over a tad will allow the operator to see the width of the ink strip remaining on the steel rider and can be adjusted accordingly. Repeat this procedure for the others.
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