Attached photo is a close-up of a 10 year old 'paper glazed' Kompac III form roll.
If your Kompacs' form roll 'reflects light', its' surface is to hard and to glazed to carry ink properly and should be replaced with a New Form Roll.
The primary cause of tone bars accross the sheet is from a miss-calibrated Kompac.
A metering roll bearing that is failing, and a 'very glazed' and to hard form roller will also cause it, and a very worn and slick/shiney metering roll will too, but the most common cause is the 'lack of milling pressure' between the metering and form roll!
Remember, the metering roll is powered by friction against the form roll.
If you do not have adequate nip pressure the metering roll will 'stall/slip' causing tone bars accross sheets.
To re-calibrate your Kompacs' nip pressure, clean it and loosen the excentric rings.
Use a .010" feeler gauge to detect metering roll parallel to the form inserting feeler gauge 2" in from roller ends (form roll's center is crowned).
Once you have achieved an even feeler gauge pull at both sides of Kompac with feeler gauge, lock set screws to set roller parallel.
Now, loosen set screws that secure indicator rings to excentric rings and move indicators to align the first indicator line.
Now, move both rings so they match up to 'center' indicator mark and you are set at what I call the 'midpoint' nip pressure setting.
From this setting (if your form roll durometer and surface finish is within specs) you can now run with the necessary moisture to print dense color.
If, you experience a 'too wet' condition at the center mark setting you can reduce moisture by increasing nip pressure, moving excentrics up further from 'center' mark.
If your Kompac runs too dry at center mark, chances are your form roller is too glazed or too hard.
If glazed, and hand scrubbing does not resolve the problem, replace form roll (also read PressTip on wet sanding metering roll and using Scotchbrite on form roll).
If glazed, hand scrub it with a good/strong ink deglazer until its surface develops a dull (not shiney) surface and the rubber offers resistance to the rub of your fingers.
As a preventive practice, I recommend re-calibrating your Kompac every year.
Re-calibration will assure you that your Kompac is in proper adjustment and insure optimum performance.
