GTO 52-2 Misregistration

We print cmyk on a two-colour gto52. We get the registration in on three corners. The fourth corner is out by about one millimeter. Please name possible causes, so I can check. Thank you.

 

registration one millimeter out on one corner of a GTO sized sheet is pretty bad. When does the registration show itself as being out? Is it out on the first pass between the first 2 colors? The second pass between the last 2 colors? Will the sheet print a single color in register on each of the 2 units? My guess without more detailed info would be that you've got an issue with sheet slipping in grippers either impression cylinder or transfer. Give us more info and perhaps we can narrow it down.

 

Here's a good test for you to try... Make 2 identical plates with a fine line grid, covering the entire area of the presses largest sheet size. With all register adjustments
(to include headstops, and cylinder tumbling) in the middle of their adjustability, print about 200 sheets of your most commonly run sheet, that shows the issue you describe, being sure to get the press up to production speed. Once youve printed 200 sheets take about 50 of these sheets, and put them back into the feeder for a second pass. Again be sure to get the press up to its production speed when printing them 50 sheets. This will show you how the 1st unit registers to itself. If the 1st unit registers to itself, then you can eliminate any misregistration from the infeed, and from the first unit impression cylinder grippers. If the second pass does NOT register to itself then you need to look at either the infeed or the 1st unit impression cylinder grippers. It should go without saying, but I will say it anyway, that the assumption here is that the press has been set up correctly with proper wheel pressures, feeder timing, side guide tension and dwell, and sheet smoothing into the press!!!
If the 1st unit does register to itself, then you will want to run them pre printed sheets through the 2nd unit. You want to be sure to lock off your rollers from dropping both ink and damper on the 1st unit but leave it on impression, when printing on 2nd unit. Then you will inspect how the pre printed sheets from the 1st unit printing registers to the 2nd unit. If the 1st unit registered to itself then you should see the misregistration when you put them sheets through again with the 2nd unit turned on. At this point it will be narrowed down to either transfer grippers, or 2nd unit impression cylinder grippers.
All of this testing assumes that you have all the cylinders rolling at the correct heights!!!

 

There was another thread with identical symptoms and went away when he changed impression jacket