uneven print

Hi, I am hoping for some assistance with getting good ink coverage on my press. I seem to face this issue often and I am at a loss as to what is not right. There is a patch across the page where the print is too heavy (i.e. too much ink) and a patch that’s much lighter. The patch runs horizontal to the lay so it’s in line with the roller. My rollers are less than 6 months old so they should not be at fault. I have also spent much time working with the roller height and this is set correctly and I do not think this is at fault either. I am starting to wonder if my magnetic base is not flat?

Please note that I am largely self taught so there may be something very basic that i am missing here. please point out the obvious!

Also note - I am printing on a 10x15 heidelberg windmill.

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Are the flaws always in the same place or do they shift?
Turn the base 180 degrees and see if the flaw moves with it (or 90 degrees if you have enough room).
Eccentric trucks wcould cause such a problem but the flaw would move up and down through the run.

Hi there-

What is your base make?

Additionally, what are your plates like? Do they seem like the flatten out perfectly on the base?

You bought new rollers- but are they quality/from a reputable source that would have machined them flat? The base rotation suggestion above would certainly show if this was an issue, once you rotate the base (NOT the plate, the entire base), you’ll be able to see if there is a roller issue or a base issue because it will either stay in the same place or move with the base.

Are your trucks durable? (The plastic can sometimes be of a poor quality and this can cause it to wear quite quickly; this would potentially stay in the same spot if it built up on the rails of the machine. If it turns into a deposit on the rails it can make a bump, for example.)

Your base- is it 100% clean before mounting plates? Are the backs of the plates 100% clean? Even a little schmutz under there can cause a headache, so you must be absolutely certain of this.

It does sound like either a base or roller problem; in the case that you rotate your base and the problem stays in the same spot, I would also rotate the rollers and see if the spot moves as well. In either case, you should eliminate pressure/press packing as a variable, inspect your platen if the problem stays in the same spot whether base or rollers rotate. Either way, mark up one corner of your base, and mark up the ends of your rollers on one side with red paint (nail polish), and blue paint, so you can tell which is which. Put it somewhere that doesn’t receive wear, like the space between the truck and the roller. This will help you distinguishing between the two rollers so you can ID which is problematic, should the rollers be the actual cause.

Good luck.

Thanks parallel_imp and HavenPress, really helpful advice.

I think I may have solved this issue. Reading through another post on here regarding uneven print someone made mention of the trucks slipping rather than rolling and mentioned adding some sort of tack to make sure the trucks turned on the rails. From there I checked my rails and they were both smooth and slightly oily so i cleaned them off and roughed the surface ever so slightly with some sand paper and this seems to have fixed the issue. Obviously the rollers were ‘smearing’ over the plate as the trucks skidded rather than just touching it.

Interesting. I am glad you found the source of your ire.

Also, thank you for posting your solution; too often questions wind up being answered but no answer is confirmed- even when the OP finds it themselves :-)