dot gain sm102 vp- pre drupa

We have an older model Hberg press here and are putting some pleasing color work on it 4/c . While this press has some years on it she can still print nice.
Recently had a 4/c job on and the yellow(4th unit) really showed some dot gain. Pulled job and ran it on a 6/c same plates and paper and job looked good.

Now I am leaning toward a packing issue because the press we ran it on has same ink and blankets. I would like to start here and work back up the unit, but the knucklehead running it is a prima dona and just may learn something.

Any feed back at all would be interesting to say the least and will certainly bve appreciated.
tx

 

You're right, start with the packing. Do you have a packing guage to measure the height of the blanket after it's mounted and torqued down, 42 lbs, retorque after 150 sheets. New blankets I'll pack to .001 under and by the end of the first M.R. it will measure .002 under bearer height, used blanket just go for .002 under, no need to compensate for drop. So you need packing behind the plate too, are you using perma packing or paper? Take the packing guage and measure the height of the plate now, looking for .004 over the bearer height. Passes all that then you can start looking at other issues like roller setting, grippers that are slipping, camfollers etc. Good luck with prima dona, been there.

 

I got perma pack under the plates and am sitting at .004, I tried to get him to take packing out don't just rely on the guage. Got to start experimenting. Must have listened today was uneventful so he tried something along the way. I was glad to hear you go the way of cam follower, we just put new rollers in 3rd and 4th units and settings are nice so I kind of ruled out rollers. I hope I can zero in on something, been doing this for 40 years and know a bit of what to try. Just good to bounce things off someone else once in awhile to double check. Thanks much for your reply.

 

although it would be nice to be able to pack press to manufacturers specs sometimes it just doest work out that way. at times you need to be able to fit printing length to other presses running in the shop. More important to me than packing exactly to specs is to maintain .004" to .005" squeeze between plate and blanket when running compressable blankets. Good to see that your using a packing guage to measure. If your mounted plate is printing .004" over the bearer with permapacks installed then i would just pack the blanket either even with the bearer or .001" over bearer to arrive at the recomended plate to blanket pressure. Then pull some dry break away solids on each unit to see how your back cylinder pressures are. The scales for back cylinder pressure can always be moved if needed!!!

 

If there was a problem with the blanket packing then the previously printed colours would have been affected also to a degree.
What were the dot gains like on the previously printed colours (KCM)?
If these were fine then the issue lies with a variable that would affect the yellow only, such as yellow ink water/ balance (this is a major one), damper and roller settings, plate to blanket cylinder setting.

If the KCM were affected also then another common issue is that the blanket is not tensioned to the correct setting i.e 55 Newtons dependant on blanket type and size. We once had a blanket tensioner which was seizing, this gave the torque wrench the impression it was at the correct tension.

 

You may have a look at the ink. Some process sets run well on one press but not on another.