Horizontal streaking

[Al Ferrari]

The two valuable pdfs from Alois shown below serve to support my point that introducing cylinder shaft support means that rigidly maintain the shaft position through the full cylinder cycle, while printing, serve to eliminate the streaks under discussion, when these are caused by cylinder bounce.


http://printplanet.com/forums/sheet...n-doopid-pressmen-m..n-bearer-collision-2.pdf - especially the Fig 22 caption.

http://printplanet.com/forums/attac...-horizontal-streaking-cylinder-bounce-ind.pdf

Al

 

[Al Ferrari]

Alois,

Can you please post the full source for the work by Trevor Bruckshaw from which that single page pdf is taken?

I have tried some online searching for his name, but have come up empty handed.

Thank you

 

[Kaoticor]

can you post a picture?

Hi John, it is wierd, but I am having a lot of trouble getting a clear picture out of it. For some reason with the screens I am using to make this color, it just doesn't turn out right on a picture or a scan... It looks very wierd and a completely different color from anywhere except afar. I'll keep trying.

 

[dabob]

Alois,

your pdfs some times emind me of this story . . .

John Godfrey Saxe's ( 1816-1887) version of the famous Indian legend,


It was six men of Indostan
To learning much inclined,
Who went to see the Elephant
(Though all of them were blind),
That each by observation
Might satisfy his mind.

The First approach'd the Elephant,
And happening to fall
Against his broad and sturdy side,
At once began to bawl:
"God bless me! but the Elephant
Is very like a wall!"

The Second, feeling of the tusk,
Cried, -"Ho! what have we here
So very round and smooth and sharp?
To me 'tis mighty clear
This wonder of an Elephant
Is very like a spear!"

The Third approached the animal,
And happening to take
The squirming trunk within his hands,
Thus boldly up and spake:
"I see," quoth he, "the Elephant
Is very like a snake!"

The Fourth reached out his eager hand,
And felt about the knee.
"What most this wondrous beast is like
Is mighty plain," quoth he,
"'Tis clear enough the Elephant
Is very like a tree!"

The Fifth, who chanced to touch the ear,
Said: "E'en the blindest man
Can tell what this resembles most;
Deny the fact who can,
This marvel of an Elephant
Is very like a fan!"

The Sixth no sooner had begun
About the beast to grope,
Then, seizing on the swinging tail
That fell within his scope,
"I see," quoth he, "the Elephant
Is very like a rope!"

And so these men of Indostan
Disputed loud and long,
Each in his own opinion
Exceeding stiff and strong,
Though each was partly in the right,
And all were in the wrong!

MORAL.

So oft in theologic wars,
The disputants, I ween,
Rail on in utter ignorance
Of what each other mean,
And prate about an Elephant
Not one of them has seen!


The pdfs that are portioned out in part and parcel sometimes and that makes them seem to be as disjointed as the deifnitions on the elephant that we got from the 6 blind guys . .. while each one in describing his part was exquisitely accurate overall it was unrecogniazble from someone who had he big picture. gettng the whole photo is the only what that you can make any sense out of anything.

bob

 

[Dan Roll]

Not as intellectual a source as Saxe, but the guys on the Car Talk radio program once postulated convincingly that a group of people knowing nothing about a subject actually know less than an individual who knows nothing of the subject. I think of this often when I attend supplier roundtables attempting to solve customers problems.....

 

[Alois Senefelder]

mmm Let me see

mmm Let me see

Gentlemen,


" There's none so blind as those who will not see"


Regards, Alois

 

[D Ink Man]

There has got to be a SILVER lining somewhere here.

Alois is correct, just SEE.

One fareaking job, and all this angst.

What about Pantone 123.........?

Let's get some meat and taters on dah table players. D

 

[Al Ferrari]

Alois,

Again: Can you please post the full source for the work by Trevor Bruckshaw from which that single page pdf is taken?

Thank you,

Al

 

[John Arneson]

Kaoticor,
I almost forgot who started this thread. Could you describe this streaking in a little more detail?
Also what year is your press and could you describe your water system to me?

John

 

[Kaoticor]

Kaoticor,
I almost forgot who started this thread. Could you describe this streaking in a little more detail?
Also what year is your press and could you describe your water system to me?

John

Hi John, sorry for the late reply.

We notice this streaking every year in the exact same spot with a particular job, but only with the entire sheet being a solid color. In this case, we are printing a 4 color brown. The streaks start about 260mm in to the print image, measuring from the lead edge. There are a few streaks, then the print seems to return to normal by the time it reaches the trail edge. Every year we print this job, it is consistently in the same spot. I ran a few samples from each unit individually, and it seems as if the streaking is on all 4. however, untill i run black ink (since its a lot easier to see with the screens) it's hard to say if it is the same magnitude or not.

We have a lithrone 28, 1998. Water system is chrome pan and oscillator with rubber metering and form roller. reverse slip nip between metering and oscillator.
currently we are looking in to our bearer pressures, but any feedback is appreciated. I tried taking pictures again, but i still cant seem to get it to come out right. none of the pictures captures the streaking. unfortunately, with this color of brown, the eye picks up on it pretty easily though. Thanks,

-K

 

[Al Ferrari]

Kaotiicor,

This entire thread, and everything you describe as having been tried, treats this problem a press problem.

Why could it not be a customer file problem???

Try making your own pages with that same cmyk brown, but made by you. Then actually put it on press to see if the streaking occurs. If you don't do this test, or something like it, then you have not proved it to be a press problem.

Why else would it occur every year, and only on this job???

Al

 

[Dan Roll]

How does Komori suggest the plate and blanket be packed relative to the bearer height on this particular machine?

 

[Joe Duffy]

I know this seems odd but it worked at one time for me.
Had a older Miller TP38 and had a similar problem, just could not get a good solid brown or forest green from the press on a number 2 coated sheet. Streaked and looked bad. Thought maybe the customer had at one time built in starvation rules but that was not the case. Tried everything on the press - just as had been outlined in this entire thread - with no solution. Washed up the press, changed our print order to CMYK from KCMY and the problem went away.
With all you have tried, it may be worth a shot.

 

[D Ink Man]

Ever drive a Silver ado?

 

[Kaoticor]

How does Komori suggest the plate and blanket be packed relative to the bearer height on this particular machine?

The APC model of that year has the blanket packed almost even with bearer height and the plate cylinder with no packing and a plate that runs .004" over bearer height (plate cylinder undercut of .008" or .2mm and a plate thickness of .012).

I know this seems odd but it worked at one time for me.
Had a older Miller TP38 and had a similar problem, just could not get a good solid brown or forest green from the press on a number 2 coated sheet. Streaked and looked bad. Thought maybe the customer had at one time built in starvation rules but that was not the case. Tried everything on the press - just as had been outlined in this entire thread - with no solution. Washed up the press, changed our print order to CMYK from KCMY and the problem went away.
With all you have tried, it may be worth a shot.

Interesting comment, I like it. Thanks for sharing!

Kaotiicor,

This entire thread, and everything you describe as having been tried, treats this problem a press problem.

Why could it not be a customer file problem???

Try making your own pages with that same cmyk brown, but made by you. Then actually put it on press to see if the streaking occurs. If you don't do this test, or something like it, then you have not proved it to be a press problem.

Why else would it occur every year, and only on this job???

Al

You make a valid point Al. In answer to this, we have tried making our own pages, and the file has been changed to different types of browns throughout the years (although close variations). The streaking still remained.

Ever drive a Silver ado?

D, please send some Silver over!

 

[Kaoticor]

Edit** Double post

 

[Dan Roll]

"The APC model of that year has the blanket packed almost even with bearer height and the plate cylinder with no packing and a plate that runs .004" over bearer height (plate cylinder undercut of .008" or .2mm and a plate thickness of .012)."

This packing setup has the surface of the plate moving at a slightly higher surface speed than the blanket, and this could cause streaks to show under some circumstances and not others. Try taking .002 from under the plate and putting it under the blanket and see what happens.......

 

[Green Printer]

"The APC model of that year has the blanket packed almost even with bearer height and the plate cylinder with no packing and a plate that runs .004" over bearer height (plate cylinder undercut of .008" or .2mm and a plate thickness of .012)."

This packing setup has the surface of the plate moving at a slightly higher surface speed than the blanket, and this could cause streaks to show under some circumstances and not others. Try taking .002 from under the plate and putting it under the blanket and see what happens.......

On our Komori's we have always ran the plate .002 above bearer and the blanket at .003 above bearer. This gives you the 4 to 5 thousands for plate to blanket squeeze while still maintaining surface speed.

 

[Deleted member 16349]

On our Komori's we have always ran the plate .002 above bearer and the blanket at .003 above bearer. This gives you the 4 to 5 thousands for plate to blanket squeeze while still maintaining surface speed.

Dan and Green Printer.

Just a comment about surface speed.

From tests it has been shown that the surface speed of the blanket is slightly affected by the amount of squeeze. The squeeze tended to make the blanket cylinder look larger in diameter. Also a shear force on the blanket will also affect the surface speed.

There is the actual diameter of the blanket cylinder measured when not running and then there is the effective diameter as a result of the squeeze and shear forces. Different blanket models can have different characteristics.

The effective diameter concept is well known for rubber covered rollers but it also exists for blankets.

My only point is that the measured diameters used to calculate surface speeds are not necessarily what is happening when these surfaces are in actual operation.

 

[Alois Senefelder]

The Forces of Pressure

The Forces of Pressure

Gentlemen,


The Plate/ Blanket Cylinders rotate through the Forces of Pressure - which is Stationary,

also the Cylinder Bearers function like a Gear with an Infinite number of Teeth.


Regards, Alois