Troubleshooting: Fixing Set-Off and Scuffing on Offset Presses

Recognizing the Defect

Set-off scuffing shows up as faint marks, ghost images, or smears on the printed sheet. The defect is easy to spot on glossy stock because the paper surface is smooth and reflective. It is harder to see on uncoated board, where the paper fibers absorb ink and mask the smudge.

Two main types of this defect exist. First, there is short-term set-off, which happens when ink from one impression transfers to another impression on the same sheet. Second, there is long-term set-off, which occurs when ink from one printed sheet transfers to the next sheet in the stack. Engineers often confuse the two because the visual result looks similar. The difference lies in the timing and the location of the mark.

When you see the issue, stop the press immediately. Continuing to run a press with set-off scuffing creates a backlog of defective sheets. You will spend more time sorting and reworking than you would have spent by pausing the machine for a quick diagnosis.

Common Symptoms and Their Causes

The table below maps the most common symptoms of set-off scuffing to their likely causes and the immediate actions needed to stop the defect.

Symptom	Likely cause	What to do
Faint mark on the reverse side of a single sheet	Ink tack is too high, or drying time between impressions is too short	Reduce ink volume, add a release agent, or slow the press speed
Dark smudge on the next sheet in the stack	Long-term set-off due to under-dried ink or high paper tack	Increase drying time, use a lower tack ink, or apply a release agent to the stack
Scuffing that follows the registration mark	Impression pressure is uneven, causing the blanket to press too hard on the ink film	Check the blanket and impression cylinder pressure; adjust the pressure knobs on the unit
Scuffing that appears only on specific colors	One ink unit is running with too much ink or the wrong ink viscosity	Check the ink feed for that unit; adjust the ink key or change the ink to a lower tack formula
Defect appears after changing paper stock	The new paper has a different surface finish or sizing that changes ink transfer	Re-run a make-ready test with the new stock; adjust the ink volume to match the paper absorbency
Scuffing on all sheets after a long run	Drying systems are not working, or the shop air is too humid	Check the ink drying system; verify that the humidity and temperature in the room are within the manufacturer’s recommended range

Diagnosing the Source

Start by identifying which impression is causing the transfer. If the mark appears on the side of the paper that has not yet passed through the press, it is short-term set-off. If the mark appears on the next sheet in the stack, it is long-term set-off.

Short-term set-off is usually a pressure or ink volume issue. Check the impression pressure on the unit that is creating the mark. If the pressure is too high, the blanket presses the wet ink into the paper surface too hard, and that ink transfers to the next impression on the same sheet. Lower the pressure until the mark disappears. Do not lower the pressure to zero. You need enough pressure for a clean transfer from the plate to the blanket.

Long-term set-off is usually a drying or ink tack issue. If the ink is still wet when the next sheet is pulled from the stack, it will transfer to the paper on the bottom of the stack. Check the ink tack with a tack ball or a similar tool. If the ink is too sticky, it will not dry properly and will hold onto the paper surface. Switch to a lower tack ink or add a drying agent if the process requires it.

Fixing Impression Pressure

Impression pressure is one of the most common causes of set-off scuffing on sheetfed offset presses. The pressure must be high enough to transfer ink from the plate to the blanket, but low enough to avoid pushing wet ink into the paper.

Check the pressure on each unit individually. Use the pressure gauge or the indicator on the press. If the gauge is not available, use a feeler gauge or a strip of thin paper to check the gap between the blanket and the impression cylinder. The gap should be consistent across the width of the unit.

If one side of the unit has higher pressure than the other, the mark will appear on that side. Adjust the pressure knob or the wedge on the low-pressure side until the gap is even. Run a test sheet after each adjustment. Do not make large changes at once. A small adjustment of a fraction of a millimeter can make a big difference in the quality of the print.

Also check the blanket itself. A worn or damaged blanket can hold ink unevenly. If the blanket has a rough surface or a thin spot, it will transfer ink unevenly and cause scuffing. Replace the blanket if it shows signs of wear. A new blanket can often fix a pressure issue that seems to be a mechanical problem.

Adjusting Ink Volume and Tack

Ink volume and tack are directly linked to set-off scuffing. If the ink volume is too high, there is more wet ink on the blanket. That excess ink has a higher chance of transferring to the next impression or the next sheet.

Check the ink feed for each unit. Make sure the ink is flowing smoothly and that there are no air bubbles in the system. Air bubbles can cause the ink volume to fluctuate, leading to uneven ink films.

If the ink volume is too high, reduce the ink key or the feed rod. Do not cut the volume so low that the print becomes light or the registration shifts. Aim for a balanced ink film that covers the plate area without overflowing onto the non-image area.

Tack is the stickiness of the ink. High tack ink holds onto the paper surface after the impression. That is why it transfers easily to the next sheet. Low tack ink releases more easily and dries faster. If you are using a high tack ink for a job that requires fast drying, switch to a lower tack ink. If you cannot change the ink, add a drying agent to the ink or adjust the press speed to allow more drying time.

Checking the Drying System

The drying system on an offset press helps the ink set before the next impression or before the sheet leaves the press. If the drying system is not working correctly, the ink remains wet longer than expected, and set-off scuffing becomes more likely.

Check the ink drying system first. Make sure the ink is the correct type for the drying method being used. For example, if you are using a waterless ink, it must be compatible with the waterless drying system. If you are using a conventional ink, it must be compatible with the ink drying agent or the heat drying system.

Check the heat drying system if the press uses it. Make sure the heater is reaching the correct temperature. A heater that is too cold will not dry the ink fast enough. A heater that is too hot can cause the ink to dry too quickly on the plate, which can lead to other defects like scratching or poor transfer.

Also check the shop environment. High humidity slows the drying of water-based inks and waterless inks. Low humidity can cause the ink to dry too fast on the plate. Keep the shop temperature and humidity within the range recommended by the ink manufacturer.

Prevention Tips for Long-Term Quality

Preventing set-off scuffing is easier than fixing it after the fact. Build a routine into your make-ready process that checks for these issues before you start a large run.

Run a test sheet at the start of each job. Run a test sheet after changing ink, paper, or press speed. Run a test sheet after a long run, because the press conditions can change over time. Keep the test sheets in a log so you can compare the quality of the first impression to the last impression.

Use the correct ink for the job. Match the ink tack to the paper stock and the drying system. If you are printing on uncoated paper, use an ink that is designed for uncoated stock. If you are printing on glossy paper, use an ink that has a lower tack and dries faster.

Keep the press clean. Ink residue on the blanket, the plate, or the impression cylinder can cause uneven transfer. Wipe down the blanket and the plate at the end of each run. A clean press runs more consistently and produces fewer defects.

Train your operators to recognize the early signs of set-off scuffing. If an operator sees a faint mark on a test sheet, they should stop the press and check the pressure and the ink volume before the defect spreads to the entire run.

When to Call for Help

If you have checked the pressure, the ink volume, the ink tack, and the drying system, and the defect persists, there may be a mechanical issue. The blanket cylinder or the impression cylinder may be out of alignment. The press frame may be loose. The bearings may be worn.

Contact your press service technician if the defect continues after a thorough make-ready. Do not keep running the press with a defect that you cannot fix. Running a press with a mechanical issue can cause more damage to the press and to the printed sheets.

A technician can check the press frame, the cylinder alignment, and the pressure mechanisms. They can also inspect the blanket and the plate for damage. A quick service visit can save you from losing a large run of defective sheets.