Disappearing dot gains?

Alith7

Well-known member
I'm hoping some of you brilliant people might be able to help me.

About a month ago, our dot gains on our sheetfed press disappeared. I mean gone. I have been compensating with a manual curve adjustment of +15% (!!!!!) at the 50 and tapered down on ALL 4 colors. I don't need any lecture on why that's a horrible plan, went through probably all of them and then some already with the owner and head pressman. As you can see, I lost that battle.

My problem is that the general consensus is "what does it matter, we're printing fine now". So I am getting NO help from either the owner, the head pressman or the operator to figure out what happened to the press. All plates have been checked and verified that they are burning correctly, and nothing has changed in the RIP. Oh, and on top of that, i'm being told that we are not reprofiling, everything is fine. -:cautious:

Aside from it being winter which makes the humidity and temp drop (but it's never been an issue like this in 20 years) any other ideas on what could cause ALL the units to lose their dot gain?

The impression pressure is controlled digitally through the console, and my thought is that something went wonky with the positioning of the cylinders, but I'm told "that's not possible".

Any help will be MUCH appreciated.
 

chriscozi

Well-known member
First blush, the profiles/settings at/going to the RIP have changed.
That can swing things dramatically.
Which RIP is resident?
 

Alith7

Well-known member
First blush, the profiles/settings at/going to the RIP have changed.
That can swing things dramatically.
Which RIP is resident?
I have gone through all the profiling in the RIP and made sure that nothing changed unexpectedly, and it all looks to be in order. This is also only affecting one of my two 4-color presses. We are using Xitron Sierra RIP.
 

Alith7

Well-known member
one is a 750 the other is a 520 so can't really do that, but it is the same plate thickness & manufacturer, same burn profile, same plate linearization curve. Different characterization profiles because different presses though. but they've historically not been much different.

For the most part over the last 10+ years, even over different plates and different presses, we've run essentially linear with a few % tweaks to adjust for grey balance and bring into G7 spec. Right now though, my characterization curve for my 750 is ridiculous! MYK are pushed 15% at 50 over where I normally am, and C is pushed almost 20%. I'm really at a loss here. I've never seen anything like this.
 

chriscozi

Well-known member
Can only be the rip or the press.
If you have the ripped tif from a previous known good job you could re-plate and see where the change happens.
If you don't have known good files you have to confirm them some other way to rule out the RIP as the culprit.
Try running the same set of calibration screen tints on the two (press) sizes of plates.
If they measure the same seems like it would be the press, no matter what anyone else says.

When you have eliminated the impossible, whatever remains, however improbable, must be the truth,
Sherlock Holmes - Sir Arthur Conan Doyle
 

Alois Senefelder

Well-known member
Hello Alith,

So you are happy that the Plates are imaged correctly (Checked via the Imaging control strip)?

Next - have you checked the Print Control Strips (Star Targets, etc. ) on the Press Sheet???

Regards, Alois
 

Alois Senefelder

Well-known member
Again Alith,

It's OK the Printers tell you that the "Impression Pressure setting are OK - BUT have they checked via Cylinder Stripe Test?

What you see on the Press Console is NOT always correct.

Regards, Alois
 

Alith7

Well-known member
Chris~
Not a bad idea on burning an old TIF, I'll give that a try. Love the quote BTW.

Alois~
I have checked the plates and yes, I'm happy with the reading, luckily i'm running processed plates right now that I CAN check.

I don't believe they have checked cylinder stripes. (pretty sure they haven't)
when I really pushed, I did get them to admit that they set the console to what it "should" be, which I guess is consistently light, and then increase pressure until it "looks good", their words. When I asked about increasing more I'm told that they then have fit problems as the image stretches. I pointed out that they have fit problems anyways (which is another battle i've been having) and the answer was "well there you go".

I'm going to give Chris's suggestion a try and burn an old set of TIF's and try that.
 

SteveSuffRIT

Well-known member
What device and settings are you using to measure the dot gain (TVI) on the plate and press sheet?
Will a different device measure the same results?
For example, if the press has a scanner what does it say?
 

Alith7

Well-known member
What device and settings are you using to measure the dot gain (TVI) on the plate and press sheet?
Will a different device measure the same results?
For example, if the press has a scanner what does it say?

for the plates, I have an old Ihara plate reader, but it's what I used to set the plate linearization in the first place, and it's saying the plate is imaging linear.

for on press, I have a handheld SpectroDens, and the in-line PDS (Techkon with Ryobi software), both are reading the same within a few points of variance, but nothing drastic.

Also ran ISO-check on my inks with the SpectroDens and everything is within tolerance.

I can say that the colorbar dot gain patches are slightly ify. On my old Heidelberg we had the Techkon retro-fit with their PDS and their software, and I can honestly say I miss that so much! Ryobi's version of the software, well frankly, it sucks. I miss being able to set up my colorbar the way I want it and being able to functionally read everything. Having dot gain patches spaced across the sheet and being able to read slur targets is something that I miss a LOT! Ryobi only lets me put one dot gain patch for each color on the whole strip, and it's way off on the ends, so if I have a light coverage job, or a smaller sheet, sometimes I don't even get to see them. I do put other control patches on the sheet (when I can) but more often than not, I don't have any room.

But, regardless of those frustrations, I have been running this press for almost 7 years, and this is the first time i've anything like this happen.
 

SteveSuffRIT

Well-known member
Out of curiosity, what are your press sheet dot gains measuring?
They should be about 16%
Paper = Gloss Coated
Ink Density = in tolerance to ISO (G7)
Screen Ruling = 175 lpi
Reference Screen Tint = 50% (AM, Linear on plate)
 

Ulrich

Well-known member
...This is also only affecting one of my two 4-color presses.
is this not a proof that in prepress everything is unchanged and well okay?

everything is fine
ask them exactly this again when a customer will confront them with a green 50(!)-0-100-0 in file on a periodically brochure which is now printed in another green or - because you had fixed it already with a correction about +15% - a gradient is involved... ;-)

I remember: We struggled once a time quite simulary in understanding when somebody in the office had bought new (cheaper of course...) rubber blankets and in another case the pressman had taken two sheets (or one thicker?) between the cylinder and the rubber blanket...

(So in your case the pressman has fixed the rubber blankets whithout any sheet on the cylinder?)

In the other direction - also comparizing two different machines - we had once much more points (about 5-7% up) caused by different fountain solutions on both machines.
 
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Alith7

Well-known member
Out of curiosity, what are your press sheet dot gains measuring?
They should be about 16%
Paper = Gloss Coated
Ink Density = in tolerance to ISO (G7)
Screen Ruling = 175 lpi
Reference Screen Tint = 50% (AM, Linear on plate)
Prior to my pushing the curves on the profile, we actually had negative dot gains. down around upper 40's.
 

Alith7

Well-known member
is this not a proof that in prepress everything is unchanged and well okay?

I remember: We struggled once a time quite simulary in understanding when somebody in the office had bought new (cheaper of course...) rubber blankets and in another case the pressman had taken two sheets (or one thicker?) between the cylinder and the rubber blanket...

(So in your case the pressman has fixed the rubber blankets whithout any sheet on the cylinder?)

In the other direction - also comparizing two different machines - we had once much more points (about 5-7% up) caused by different fountain solutions on both machines.
I would agree with you on the prepress part, but it's always guilty until proven innocent with prepress.

I asked about blankets, they say packing is normal, and it's the same blankets we've been running for a while.

we haven't changed fountain solution, but normally when I've seen that be the issue it affects one color more than another. magenta being the most sensitive, black & yellow usually the most resistant.
 

chriscozi

Well-known member
Chris~
Not a bad idea on burning an old TIF, I'll give that a try. Love the quote BTW.
That has been one of my favorites for a long time now.
Since at least the teenage years.

And another quote described as Hanlon's Razor comes to mind (not neccessarily in this case)
"Never attribute to malice that which is adequately explained by stupidity,"
anytime that I am frustrated by evidence of intransigence, lack of motivation, or incomplete communication.
I regularly remind myself I need to PROVE malice. Sigh.
:)
 

Alith7

Well-known member
And another quote described as Hanlon's Razor comes to mind (not neccessarily in this case)
"Never attribute to malice that which is adequately explained by stupidity,"
anytime that I am frustrated by evidence of intransigence, lack of motivation, or incomplete communication.
I regularly remind myself I need to PROVE malice. Sigh.
:)
Too true! No quote to reference, but I have often found that most people can't admit ignorance, they would rather bluster, deflect, and out-right lie to not have to admit they don't know something. I find this the MOST frustrating thing someone can do!
 

danremaley

Well-known member
I'm hoping some of you brilliant people might be able to help me.

About a month ago, our dot gains on our sheetfed press disappeared. I mean gone. I have been compensating with a manual curve adjustment of +15% (!!!!!) at the 50 and tapered down on ALL 4 colors. I don't need any lecture on why that's a horrible plan, went through probably all of them and then some already with the owner and head pressman. As you can see, I lost that battle.

My problem is that the general consensus is "what does it matter, we're printing fine now". So I am getting NO help from either the owner, the head pressman or the operator to figure out what happened to the press. All plates have been checked and verified that they are burning correctly, and nothing has changed in the RIP. Oh, and on top of that, i'm being told that we are not reprofiling, everything is fine. -:cautious:

Aside from it being winter which makes the humidity and temp drop (but it's never been an issue like this in 20 years) any other ideas on what could cause ALL the units to lose their dot gain?

The impression pressure is controlled digitally through the console, and my thought is that something went wonky with the positioning of the cylinders, but I'm told "that's not possible".

Any help will be MUCH appreciated.
I’m thinking something in the RiP got corrupted. . . Maybe reset it & re-liberalize. Press ALWAYS gain - seldom sharpen.
I have the RiP “wanted” numbers if that helps.
Dan 412.889.7643
 

Alois Senefelder

Well-known member
Hello Alith,

I'm puzzled by some of your replies!

1) IS the CtP Imagesetter producing - Production Compliant - Imaging/Plate?

2) Surely there must be room somewhere for a PrintControl Strip.

3) What do you mean by Ryobi - only lets you put 1 Dot Gain Target?

4) Are you applying "Curves" to the PrintControl Strip - if so - why?

5) What happened a month ago in the Press Room for this problem to become apparent?

6) Has a "Print Test Forme" ever been used to test the Press?

Regards Alois
 

Alith7

Well-known member
1) IS the CtP Imagesetter producing - Production Compliant - Imaging/Plate?
---> Yes. Tested and confirmed.

2) Surely there must be room somewhere for a PrintControl Strip.
---> On some jobs, yes, haven't had a chance to look at what's running to see what I can squeeze on, we're right in the middle of our big twice a year order and no one is letting me mess with anything right now.

3) What do you mean by Ryobi - only lets you put 1 Dot Gain Target?
---> Ryobi's closed-loop system will only work with Ryobi's supplied colorbar, yes, I could put other patches on that aren't read by the PDS, but again, not being allowed to mess with things right now.

4) Are you applying "Curves" to the PrintControl Strip - if so - why?
---> I'm not sure what you mean by this? I'm don't know what other RIP systems can do, but I don't get to pick and choose what part of a layout gets different calibrations applied to it. My only option is the whole layout gets processed with the same calibration curve to generate the plate TIF. Unless I double burn a plate with two different TIF's. But that's a whole different set of complications. If you're talking about linearizing the plates, then I do what I have always done, which is send over a linear 0-100 control strip, read that, and apply that adjustment to the plate profile. Then from there I run a control form and generate a characterization specifically for each press.

5) What happened a month ago in the Press Room for this problem to become apparent?
---> No offense, but if I knew THAT, I wouldn't be asking here. I have drilled through repeatedly with the pressmen to find out what they did, and they "claim" that they didn't change anything.

6) Has a "Print Test Forme" ever been used to test the Press?
---> Yes, regularly, whenever something drastic is changed. Like new rollers and such. As well as I try to run a G7 check and curve adjustment about every 6 months as the seasons change. I had not run one yet for this winter due to a lot of craziness going on in the shop, and now that we have this problem, I'm hesitant to run a reprofile until I have it figured out.

However, that being said, even with reprofiling, we're normally adjusted between -3% to +2% at 50% on my characterization curve. I have never had to go higher than that in all the adjustments. I am currently running at around 64% on all the colors.
 

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