| This audiovisual, Cylinder Alignment and Adjustments, is directed to the offset press operator who has considerable experience in press operation. A clear understanding of alignment and adjustments procedures is vitally important to quality press reproduction. |  |
| Due to the stress and strain to which cylinders of an offset press are subjected, the alignment of the cylinders must be occasionally checked and readjusted. |  |
| To help better understand the alignment and adjustment procedures of the printing unit, this section will refer to presses that have plate and blanket cylinders which run with bearer-to-bearer contact. This is often described as "running on bearers." |  |
| With the exception of small duplicators, metal decorating, and some European presses, all offset press blanket and plate cylinders have bearer-to-bearer contact when running on impression. The intended purpose of these cylinders riding on bearers is to smooth out the flow of power to prevent "gear streaks," |  |
| Presses with plate and blanket cylinders that run on bearers are designed to run with firm, specific bearer-to-bearer pressure. If this pressure is not maintained--because of worn journals or bearings--the transfer-squeeze pressure developed through overpacking would force the cylinders apart and lead to probable printing problems and premature press wear. |  |
| Gears work best and with least wear when the pitch lines of each gear exactly coincide. |  |
| Therefore, if the cylinder bearers are forced apart by the transfer-squeeze pressure, the pitch lines of the gears are also held apart and no longer coincide, causing a slipping, irregular drive. This may cause slurs and streaks, shortened plate life, and premature gear wear. |  |
| A press operator should be able to check the cylinder alignment and bearer pressures on the press. There are several methods of checking cylinder alignment and bearer pressures. In addition to the ones described in the AV, other methods may be found in press manufacturer's instruction and maintenance manuals. |  |
| A periodic, quick-check method to determine whether alignment adjustment is necessary can be used on small- and medium-size presses. First, put on a plate and blanket and pack to bearer height plus .002" to .005", depending upon the type of blanket, size of press, and manufacturers' recommendations. |  |
| Make certain that the plate is gummed up. Ink up the entire plate by running the press with the ink form rollers on and dampener forms off. When the plate is fully inked, lift the ink form rollers and stop the press in a position where the cylinder gaps are not facing each other. Following the manufacturers' instruction for the particular press, manually throw the plate and blanket cylinder on impression then off again. |  |
| This will leave a inked stripe across the blanket cylinder. If the cylinders are parallel, the width of the stripe will be equal from one side to the other. If the stripe is not the same width all the way across, the cylinders must be realigned. |  |
| The same procedure can be used to determine the parallel alignment between the blanket cylinder and the impression cylinder. When making this check, first increase the distance between the blanket and plate cylinder so they will not touch when the press is run on impression. |  |
| The blanket cylinder is then inked solid and an inked stripe transferred to the impression cylinder by manually contacting the blanket and impression cylinder after the press is stopped. |  |
| Parallel alignment of the blanket and impression cylinder can also be checked with roll solder. To do this, manually put the press on impression. Then feed strips of roll solder between the blanket and impression cylinder bearers. This is done on both ends of the cylinders at the same time. Jog the press forward several inches. As the solder is fed in, it compresses to a thickness equal to the distance between the bearers. |  |
| After several inches of solder have passed through the nip of the bearers, reverse the press, remove the compressed solder strips, and "mike" their thicknesses. If the cylinders are parallel, the thickness of both strips of compressed solder will be the same. |  |
| Next, a test for recommended bearer pressures should be made. The transfer of inked thumb prints from the blanket cylinder bearers to the plate cylinder bearers, when the press is on impression, is used to determine bearer-to-bearer pressure and cylinder alignment. The cylinders should be over packed a bit beyond the normal transfer-squeeze pressure. The amount of overpacking depends on the make and size of the press: .002" to .003" may be sufficient on a 26: press. On some of the very large presses, as much as .008" is required. |  |
| This method is only valid if thumb prints are applied properly to the blanket cylinder bearers. The thumb print must be clear, with definite print lines without fill-ins or smears caused by excessive ink or poor application. Shown here are examples of good and poor thumb prints. The bearers must be spotlessly clean and free of any oil film in order to get an undistorted transfer. |  |
| Some press operators prefer to use stenciled images such as diamonds or circles. Instead of thinned ink, they may use machinists' red lead or even lipstick. Under good bearer-to-bearer pressure, the stenciled images will transfer and also show definite spread that is identical on all the bearers. Once again, to be a valid test, the ink must be tapped down as thin as possible. |  |
| Prepare the press for this test by overpacking, for example, an additional .004" bringing the total packing to .006" above bearers. This is best done with a new blanket mounted on the blanket cylinder. To repeat, the exact amount of overpacking depends on the make and size of press. |  |
| Next, put four thumb prints or stenciled images around the blanket cylinder bearers in the area of the cylinder gap, 3" beyond the lead edge of the cylinder body, opposite the cylinder gap, and 3" before the trailing edge of the cylinder body. |  |
| Run the press on impression for just one revolution. Stop and check the image transfer on the bearers. If there is proper bearer pressure and cylinder alignment, the images should transfer uniformly from the blanket cylinder bearers to the plate cylinder bearers in the area of the gap as well as the other three points. |  |
| If bearer-to-bearer pressure is insufficient, the additional overpacking will force the cylinder bearers apart, causing a poor image transfer at the image checkpoints around the cylinder bearer in the area of plate and blanket contact. At the gap of the cylinders, there may be a good image transfer since there is no plate-blanket contact that would force the cylinders apart. Also, if the cylinders are not parallel, the corresponding images at opposite ends of the cylinders will appear weaker on one side than on the other. |  |
| Once again, it is strongly recommended that the press operator check the manufacturer's manual before attempting to realign press cylinders. Manufacturers usually recommend that a qualified press machinist do this type of work. |  |
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To realign the plate and blanket cylinders and adjust bearer-to-bearer pressures, the following method can be used.
First, remove the blanket and clean the bearers. |
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| If the press has an antibacklash (split) gear, loosen and align the narrow backlash gear with the drive portion of the gear. Now, manually put the press on impression. |  |
| Second, loosen the lock nuts on the plate-to-blanket tie-rods located on both sides of the press. |  |
| Third, manually put the press on impression and turn the adjusting nuts or turnbuckles until a .006" thickness gauge fits snugly between the bearers on both sides of the cylinder. Tighten the lock nuts. If the adjustments have been properly done, a .007" gauge will not fit and a .005" gauge will be loose. |  |
| Fourth, remove the .006" thickness gauge and insert a .002" thickness gauge. Loosen the locknuts and tighten the nut or turnbuckles, carefully counting the number of nut faces, or holes, until the drag or pull on the .002" gauge is the same as the drag was on the .006" gauge. From this you can not determine the number of faces that must be turned to move the blanket cylinder .001". Caution: This does not apply to presses whose adjustment is accomplished by means of eccentrics, which is true for some of the duplicators and small presses. |  |
| At this point, you may be asking, "What are faces, and how are they counted." All adjusting nuts or turnbuckles have either six flat sides or holes for a pin wrench. These flats or holes are called faces. |  |
| By marking the position of one face, then turning the nut, each succeeding face that passes this mark is counted, and specific calculations can be made from this. |  |
| For instance, if you have found that 12 faces were turned while going from .006" to .002", you would then know that a turn of three faces is equivalent to .001" movement of the cylinders. |  |
| With this calculation, it is now possible to set the bearer-to-bearer "pre-loaded pressure" that is recommended by the press manufacturer. The pre-loaded pressure is the extra pressure that must be applied between the plate and blanket cylinder bearers to hold them in firm contact when the cylinders are over packed for transfer-squeeze pressure to insure good reproduction. This pressure is generally equivalent to additional turns of the adjusting nut beyond the point at which the bearers are just touching. Using our example, if the pre-loading pressure is .004" and the bearers are .002" apart, the faces must be turned enough to move the blanket cylinder bearer a total of .006". Therefore, the nut or turnbuckle must be turned 18 faces--3 faces for each .001" movement of the blanket cylinder. |  |
| After adjustments have been made, tighten the lock nuts by holding the adjusting nut or turnbuckle firmly with one wrench and the locknut with another. It is important to retighten the lock nuts every time an adjustment is made on the nut or turnbuckle, and before checking the result of the adjustment. |  |
| Check the bearer pressures again. Overpack the blanket cylinder as before, put new thumb prints or images on the blanket cylinder bearers and run the press with impression on, for one revolution, to transfer the images. |  |
| If all the images transferred properly, it can be assumed that the desired pressure has been set. |  |
| If only the image in the gap area transferred properly, the cylinders have separated due to bearing wear. |  |
| Additional pressure can be added by turning the adjusting nut or turnbuckle, turning the faces on both sides equally, until the bearer pressure transfers the images properly around the cylinder. If the amount of turns is excessive, this indicates the bearings are badly worn and should be replaced by a qualified press machinist. |  |
| After the final adjustment has been made and the lock nuts tightened, take out the extra overpacking and run the press on impression to check for excessive pressure. If pressure is excessive, the press will slow down and strain when coming "on impression." If this occurs, the pressure must be decreased to prevent undue wear. |  |
| Once the pressures have been set, the split gear must be realigned. It is imperative to check the manufacturer's manual for its recommendations. In general, loosen the retaining bolts, shift the backlash gear--the narrow gear--away from the drive direction slightly more than the amount necessary to prevent backlash. Snug-up the bolts, but do not tighten them. |  |
| Next, run the press on impression; this will push the backlash gear into proper alignment. Stop the press and tighten the retaining bolts. Most presses equipped with helical gears do not have backlash gears. |  |
| Finally, check the alignment and distance between the blanket and impression cylinders. To do this, set the blanket-to-impression-cylinder indicator at zero and put the press on impression. |  |
| Since the impression cylinder bearers are cut below the surface of the cylinder body, there will be a gap between the blanket cylinder bearers and the impression cylinder bearers. If the distance between the cylinders is correct and parallel, thickness gauges equal to the impression-cylinder bearer undercut will fit snugly between the bearers. |  |
| If the gaps are not correct or equal, loosen the blanket-to-impression-cylinder tie-rod on one side and adjust until the gaps are equal to the bearer undercut on both sides of the cylinder. |  |
| This method of cylinder alignment can also be used on presses that run without bearer-to-bearer contact or "off bearers." These presses have cylinder bearers but they are cut below the pitch line of the cylinder gears. |  |
| Using thickness gauges to determine the distances between the bearers, cylinder parallel checks plus additional squeeze pressure can be made according to manufacturer's specifications. |  |
| When done properly, this will assure good alignment at the gear pitch lines when on impression--preventing gear streaks--and will also assure good plate-to-blanket pressure when both are packed to recommended height. |  |
| The End. |  |