Why setting matters more than compound choice
Accurate roller setting is one of the most vital functions a pressman performs. An improper setting wastes the entire efficiency of the inking unit — it damages plates expensively, wears rollers unevenly and degrades print quality — and no compound, however good, will compensate for it.
Settings have to be exact because ductors, distributors and form rollers are driven by roller surfaces, not by gears. All rollers except gear-driven steel rollers operate through contact friction, so an irregular surface adversely affects ink transfer directly.
Rollers should be set as lightly as possible to still accomplish their intended function, namely, to transfer ink to the plate.
Once locked, and unless the plate cylinder diameter changes or rollers are replaced, the adjustment requires no further modification.
How to test a setting
- Take a contact picture: wash the plate clean, lock inked rollers against it, then examine the stripe pattern at several points across the face
- Use paper strip testing — a narrow strip between two wider ones — to feel proper contact
- On flatbed presses, back off the sockets and bring them back individually until they just touch the roller shafts
- Confirm the lowest area of the roller touches the lowest area of the form
- Check that the fountain roller moves, so it does not stop in the same position each time
- Recheck the setting after a short running period and adjust if necessary
Streaks at the gripper edge
Most streaks occur at the gripper edge. Timing the inker to accommodate the cylinder gap addresses the majority of them. On an older press with accumulated wear, starting earlier on the back side of the plate takes up the excessive slack before the cylinder reaches the gripper.
Keeping settings honest
- Replace worn sockets and build up worn spindles — a setting cannot be better than the bearing it sits in
- Set every roller as lightly as possible: the 'kiss' setting
- Avoid jarring movements, which spring cores and cause runout
- Maintain uniform tension at both ends throughout
- High-speed newspaper work needs very light settings, especially for ROP colour
- Recheck and reset composition rollers more frequently — humidity and atmospheric conditions expand them
What a wrong setting produces
Set too high
- Partial squeezing, so insufficient ink or dampening solution transfers — bad printed image
- High energy consumption, heavy temperature rise and cooling problems
- Premature material fatigue, with burst danger and risk of core bonding separation
- Higher printing plate abrasion from form roller pressure
Set too low
- Irregular or interrupted ink and dampening solution transfer
- Ink–water balance disturbance, leading to scumming or smearing
- Excessive dampening application, causing faded printouts and smearing
- Bad transport and slippage — form rollers wipe ink beyond the dots and fill open plate areas
- Insufficient tolerance and vibration compensation
Set unevenly
- One side opens too wide while the other is over-squeezed — one-sided smearing and scumming
- Local overheating on the high side, with danger of cover or core bonding failure
- One-sided abrasion that destroys the cylinder form
Left at rest under load
- Lasting deformation and concentricity deviation of the cover
- Streaks in the print-out
