What Is a Repeating Defect, and Which Roller Is It On?
A repeating defect is the same problem appearing again at a fixed distance. If the distance equals the circumference of a roller, the problem is on that roller. Circumference is diameter multiplied by 3.1416; for the plate roller, include the plate and double-sided tape. If it doesn't match any of them, it is not a roller on your machine.
A repeating defect is the same flaw appearing again at a fixed distance. If the distance equals the circumference of a roller, the flaw is on that roller. Circumference is diameter multiplied by 3.1416; for the plate cylinder, include the plate and double-sided tape. If none of the rollers match, it is not a roller on your machine.
How to match it to a specific roller
Measure the center-to-center distance between two defects of the same type in the web travel direction; this is the repeat length. List every roller on the machine that contacts substrate or ink: plate cylinder, blanket cylinder, anilox roller, impression cylinder, chill roller, guide roller. Calculate the circumference of each using its own working diameter. A difference of 2 to 3 mm can count as the same roller; a difference of an order of magnitude means it is another roller, or the repeat from the previous supplier of the incoming material.
Do not pair different types of spots together. A pinhole followed by a dirt spot—the distance is meaningless.
Common attributions
| Matched circumference | Common defects | Look first |
|---|---|---|
| Plate cylinder | Plate damage, double-sided tape bubbles | This set of plates |
| Anilox roller | Impact damage, dried ink | Roller surface, not the plate |
| Chill roller or guide roller | Indentations, scratches | Whether the roller surface has raised spots |
| None match | Incoming material | Unprinted film edge |
Do this first this round
- Match only the same type of defect.
- Multiply diameter by 3.1416, write it on paper, then compare.
- Only address the roller that matches.
