“I can’t get my folding machine score (or perforation) to run straight." It’s a question we hear from operators of folding machines and scoring machines on a regular basis. We’ve seen the problem stump the experienced bindery pro as well as the novice.
The crooked score or perf will probably take one of the three forms illustrated below. Fig. 1 illustrates a score line that is itself straight, but not perpendicular to the lead edge. Fig. 2 shows a line that ‘tails off’ at the trailing edge of the sheet. Fig. 3 shows a score that is bouncing back and forth. It might also be a combination of any two or three, just to make it more interesting.
First and most importantly, don’t forget to check all the basic items. We get so accustomed to moving from one folding job to another without having to adjust ‘basic’ items that it’s easy to overlook them when a new problem appears. It’s the 80-20 rule at work. 80% of your problems will come from 20% of all possible causes and in our experience these are usually basic in nature.
So what’s a ‘basic’ item to include on your folding machine checklist?
- The sheet itself. Is it square? Are all the sheets cut the same? Is curl causing a problem?
- Is the side guide square to the first roller? When in doubt, start with the side guide squared up to fold roller #1. Or if you are running a scoring machine, be sure the infeed guides are squared up to the shafts or the register table, if so equipped.
- Sheet registration going in to fold roller #1. It must be consistent. If not, check the feeding, register marbles and register table belts.
- Fold roller tension.
- Deflector blades. To start with, be sure they are pushed in, that they are free of dings or burrs, and that they are not bent.
- Fold roller cleanliness and condition.
- Folding quality. If you are folding the sheet prior to scoring or perfing, be sure the fold is perfect. If it’s not, you’ll never be satisfied with the subsequent score or perf.
If you’ve checked these items and the problem persists, determine whether the problem is consistent or inconsistent. In other words, is every score in the same position or does it change position on the sheet?
In the case of inconsistent registration, you may want to take a look at how you have the pull out wheels set up. The article here on slitter shaft setup goes into more detail on why pull out wheels (gripper rollers) affect scoring and perf registration and offers tips on improving your results. You’ll also want to check out the article Get More Use from Folding Machine Pull Out Wheels for additional info and options. The symptoms you see in Fig. 2 above usually indicate a problem with pull out wheels and/or other tools being used on the shaft.
In the case of consistent registration, where every sheet is identical but just in the wrong position, the solution is a simple one. One side of the sheet is traveling too slowly through the fold rollers. You can speed that side up by cocking a fold plate (with closed deflector) on the opposite (fast) side. Usually plate 3 or 4 is used. Unlock the fold plate on the fast side, (left hand side in our drawing) and pull it out about 1/16", then re-lock. Repeat the process until the score is straight. For severe problems, use two fold plates and make smaller adjustments in each rather than one large adjustment in a single plate.
By pulling the deflector away from the fold rollers in this manner, you’re making this side of the sheet travel farther than the opposite side. Since this takes longer, it effectively slows that side down.
The idea is illustrated here in this pdf about how to straighten perforations on 16pp signatures. The job is slightly different but the concept is the same.
Of course if you continue to struggle despite all these basic efforts, you may want to have a mechanic give your folding or scoring machine a quick checkup. Worn items such as bushings, bearings, gears, drive belts and shafts will also contribute to crooked scores and perfs.