Accurate registration is a must with today’s demanding quality requirements. If registration (especially “high-to-low” registration) is a problem on your Goss Urbanite press, the plate lock-up bars should be calibrated.

Calibrating your plate lock-ups will improve the quality and consistency of color registration in your printed products. Below is an outline of steps that can be followed to perform an accurate calibration of the plate lock-ups on an Urbanite press:

* Inspect the plate punch.

* Make sure the pins that position the plate punch both horizontally and vertically are not worn.

* Begin punching plates one at a time.

* Make sure that the punched holes in the plate are cleanly punched. Be sure there are no burs caused by a damaged punching die.

* As you are punching the plates, check that the plate punch is punching consistently by measuring, on several plates, the distance from the punched holes to the plate edge. Be sure that they are all the same so that the plate bend can be accurately measured.

* Inspect the plate bender.

Check the pins on the plate bender for wear and loose movement.

* Check that the plate bender is bending consistently. Use a dial caliper to measure the distance of the plate edge to the bend on several plates.

* Check the plate bend for a square/even bend. A consistently crooked bend will cause registration problems for the S-wrap/Direct color position.

If accessible, a plate verifier could be used to check the accuracy of the bend and image on all of the plates.

* Remove all of the lock-up bars.

* Clean the bars and remove all of the shims. Clean the cylinder gap. Thoroughly clean the lead edge slot on the lock-up bar. Be sure to reinstall the same lock-up into its original plate gap. This will help ensure that the side register will be close on the first grid test.

* Carefully burn several plates with a hairline grid. The hairlines on the grid (see Figure 1) should be separated by only .5-inch to 1-inch, both horizontally and vertically. Be sure that the plate burner pins are in good condition and the vacuum drawdown is correct before flipping the burner top. Use the same two negatives to make all of the plates. Do not tape the negatives together.  



Fig. 1

* Use two people to carefully install the plates on the press. Only prepare and print a test on one side of one color lead at a time. Be sure to mark the low plate for each color.

* Print three separate tests runs using new plates for each press run. Set the register on the top left side of page 1, on the Low plate position, for every test run.

Note: When setting the register, be sure that the image area is properly centered with the page margins and properly aligned with the half fold.

* Evaluate all three test runs and move the lock-ups accordingly for any position that is consistently misaligned. (See figures 2 to 4 for lock-up adjustments.)  



Fig. 2

Note: If any of the sidelays are near the end of their adjustment, move both the high and low lock-up bars accordingly to center the sidelay adjustment.

* Replate only where needed and print another test.

* Evaluate the grid and reposition the lock-ups that are not properly aligned.

Repeat steps 8 and 9 until the registration is acceptable to you. Acceptable copies should take into account any fan-out, sheet contraction, or any other condition that does not pertain to the lock-up itself.

To move the grid/lock-up toward the operator side, loosen the Allen setscrew (see Figure 2) on the operator side lock-up block and tighten the Allen setscrew on the drive side lock-up block.

To move the grid/lock-up away from the operator side, loosen the Allen setscrew on the drive side lock-up block and tighten the Allen setscrew on the operator side lock-up block. The jackscrews (see Figure 3) and register screws (see Figure 2) must be loosened before a horizontal adjustment can be made.  



Fig. 3

To make a vertical adjustment, both jackscrews must be loosened (turn them clockwise) and the register screws on the lock-up block must be adjusted so that shims can be placed under the lock-up. Mylar strips are normally used as the shim. Placing shims under the plate lock-up will advance the image toward the bottom of the printed page. The Mylar should be cut into approximately 10-inch strips so that they can be placed between the jackscrews. The Mylar strips can also be placed only under one side of the lock-up if the image is crooked.

Note:  After any lock-up bar adjustment is made, the jackscrews and register screws should be tightened to secure the bar to the bottom of the plate cylinder gap.  

Fig. 4

Accurate measurements of both horizontal and vertical alignment can be taken by using a microscope with a scale in thousands of an inch (see Figure 4). Knowing exactly how much to move a plate lock-up will save time, because fewer adjustments normally have to be made.  



Fig. 5

Horizontal adjustments made to the lock-up bar can be accurately measured by using a pin alignment tool and a dial indicator (see Figure 5). The alignment tool fits in the lead-edge gap and has a notch to fit securely to the lock-up pin. The dial rests against the frame of the press and will give an accurate measurement of horizontal movement as an adjustment is being made to the lock-up bar. This tool also saves time by taking the guesswork out.