Disappearing dot gains?

SteveSuffRIT

Well-known member
Side by Side comparison.
Left-Old_New-Right.jpg
 

Alith7

Well-known member
My you guys were busy over the weekend! Apologies for not coming back sooner, was buried in homework for a business class.

Thank you Steve for fixing the comparison to be easier to see the differences!
ON that note, here is a better one of the printed piece.
comparison.jpg


I will take a look and try to find some solid thin text or see if I can get the few slur targets looked at.
Unfortunately, the 50x that I took these photos with is the best I have for magnification.

I asked about blankets and packing, and am told that it's the same as always. I asked if they mic'd the blankets before putting them on and was told that they don't really have a micrometer for the blankets, it's for the paper and doesn't take a good reading on the blankets. So i'm working on that. I have a different micrometer that I use that should work for that.

Alois~ That is exactly my point. And now that I have re-imaged an old TIF set there's definitely something going on. But! I haven't eliminated the plates entirely yet. The plates are AGFA TU, and when we ran AGFA plates years ago, I vaguely remember having a problem where the dot scanned fine out of the processor, but it wasn't burning right and when it went on press, the edges of the dots dropped off.

They have a full schedule today, but the boss is gone tomorrow, and we're getting caught up on production, so we're going to try to get some testing done. I'll keep you guys updated.

At least it appears I'm keeping you entertained. ;):sneaky:
 

Alith7

Well-known member
as requested, here is the slur target comparison on the Cyan and Black.
I don't have star targets unfortunately.
Cyan-Slur.jpg
Black-Slur.jpg


Also, please note that the slight doubling on the "Old" half is from my shakes. after about 15 attempts, that one was just NOT wanting to photograph clearer.

Curious what you guys see. I see minimal difference, but the "old" lines do appear less crisp to me, slightly blobby.
 

Alois Senefelder

Well-known member
Alith,

Micrometer !

Beg, borrow, steal or BUY a Soft Materials Micrometer.

Regards, Alois

Amazon !!!!
 

Attachments

  • Micrometer for Soft Materials # 1097.pdf
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Alith7

Well-known member
Alois, That is almost exactly the one I am giving them, but mine is manual guage, no digital.
 

cementary

Well-known member
I asked about blankets and packing, and am told that it's the same as always. I asked if they mic'd the blankets before putting them on and was told that they don't really have a micrometer for the blankets, it's for the paper and doesn't take a good reading on the blankets. So i'm working on that. I have a different micrometer that I use that should work for that.
it's not only packing under the blanket, there is also packing under the plate. Also, don't know about Ryobi, but on ManRoland press operator can easily ajust plate-to-blanket squeeze by with these little hand wheels:
изображение_2021-02-16_102622.png

PS if you use all the same blankets and packing from same manufacturers over the years, i really doubt that there can be a change in thinkness that high.
 

alibryan

Well-known member
If I remember correctly the Ryobi 520 doesn’t use any packing under the plate at all, and if the 750 uses it, it’s using cylinder Perma-Pak under the plates due to having semi-auto plate hangers. Perma-Pak is something that you don’t change from run to run, you basically affix it to the plate cylinders one time, and then leave it on after that.

Also, a micrometer is not the correct tool to use for accurately measuring printing squeeze between cylinders... for that you need a packing gauge. It’s a pretty standard tool for any pressroom that’s printing dots, and most competent operators will (hopefully) know what one is, and how to use it. If the amount of squeeze is something that’s in question, you’re ideally looking for a total of about .003-.004 squeeze between the plate and blanket cylinders.
 

Alith7

Well-known member
alibryan is correct, Ryobi does not use packing under the plate, although the Perma-Pack does sound familiar, I'll ask about that.

Our press is only 6 years old, so we do have the semi-auto plate changers, and as far as adjusting the pressures, that is all handled through the console because ours has the collapsible drum system to run text weight up to 31pt board stock.

My thought was that however the console gauges position of the cylinders got messed up, so it thinks the spacing is different than it actually is. However my pressmen say that their process is to set the pressure to what it "should be" for the stock weight to start and then increase pressure a few points until the image improves.

My next question was: what about applying more pressure? and they said that if they increase pressure any further the image starts to distort and cause registration issues.

I know a micrometer won't measure between cylinders, but it can check to make sure the blanket thickness didn't change. Bad manufacturing batch or something. I don't believe we have a pressure gauge for checking squeeze, but I will ask.
 

cementary

Well-known member
Perma-Pak is something that you don’t change from run to run, you basically affix it to the plate cylinders one time, and then leave it on after that.
true, but it doesn't mean that it is correct thickness perma-pak from the start. Modern compressible blankets allow up to .008 (0.2 mm) exessive squeeze
 

Alith7

Well-known member
Alibryan, that all fits with my understanding of things, so we are on the same page there. I'm still pretty sure we don't have a packing gauge, but I will check.

The profiles we've been running for the last couple years (until now) have had the Cyan pulled back, not 100% sure on why, but it's what was needed to match calibrated proofs and pass G7 and grey balance. And (normally) on scans, the 50% dot gain patch would read at the targeted 65-67%. My 520 has similar curves.

Updates from today: we tested a plate from the other plate burner, and the print is exactly the same, so we have now successfully eliminated the RIP and the plate burner. This bring a question of a bad batch of emulsion on the plates? We did just have a plate lot that all had a huge dent in the middle that we had to return, so QC is not at 100% right now.

Not sure if this helps or not, but here is an updated comparison with a screenshot of the TIF preview added.
This is the same plate TIF used for both prints stored from the plate burner. it was not reprocessed through the RIP in any way.
What it looks like to me is that there is almost zero gain from the TIF image currently.

comparison-w-tif.jpg


Here are screenshots of the Dot Gain patch direct from the TIF previews. It really shows how much I am currently pushing the curves to match what I was previously running.

Screen Shot 2021-02-16 at 10.26.47 AM.png
Screen Shot 2021-02-16 at 10.30.07 AM.png
 

Alois Senefelder

Well-known member
Alith and fellow Lithographers,


Clarification: As describe by Alibyan, the ultimate tool is "Blanket Height Gauge" but the Mechanics of Cylinder Pressure Settings

on modern Offset Presses provide via the Blanket Cylinder eccentric bearing to and away from the Impression Cyl. Because this Cylinder is in

fixed bearings. Rare to find Presses that adjust the Impression Cyl. ---- now back to the ongoing problem!


Regards, Alois


See PDF
 

Attachments

  • Cyl pressure settings # 1098.pdf
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Alith7

Well-known member
Very helpful! thank you!
I've been trying to find a diagram of how the collapsible drums work without success. :(
I know I saw something back before we bought it, but no luck now.
 

alibryan

Well-known member
Have you tried measuring something like all of the steps on a linear gradated control strip, before and after press (processed plate and printed on paper), to see what your actual gain is?
 

SteveSuffRIT

Well-known member
The Tiff previews in post #54 are more than the actual press dot gains in post #41.
This doesn't make any sense to me?
Does the plate imaging look the same as the Tiffs?
 
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Alith7

Well-known member
Have you tried measuring something like all of the steps on a linear gradated control strip, before and after press (processed plate and printed on paper), to see what your actual gain is?
Not specifically, but but it's a good idea. Also to measure the plate before, the printed image, and the plate after they run to see if it is the plate breaking down. Although I would think I'd see other issues if it was bad plate emulsion. But maybe not. I'll try to get some gradated steps on one of the upcoming runs.

The Tiff previews in post #54 are more than the actual press dot gains in post #41.
This doesn't make any sense to me?
Does the plate imaging look the same as the Tiffs?
The press dot photos from post #41 are from printed TIFs using the previous profile, so they would reference the screen shot of the TIF that is labeled "Previous Profile" in post #54. The screenshot in post #54 that is labeled as "Current Profile" is what my current curves look like. I have not specifically pulled printed dots from that profile yet. I only showed the two to make clear just how much I am having to push things right now to match my previous print runs.
 

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