printlength issues. constantly.

[spigot]

Hi all, im having a few quality control issues on the press.
I always have large inconsistencies in print length, which manifests itself at the last print unit.
I have the colour order C-M-Y-K. This is due to the type of work we do, it means 50% less washups.
The plates are still manually made, from film created on site.

By the timei lay down the black, its frequently 1mm or more too long. So i reduce the plate tension, (slacken bolts) to get it to fit, however it seldom does, and reversings look fuzzed.

The press is an older stlye Speedmaster 102. Conventional damping. I have calibrated the packings to 0.05 squeeze. (dot gain issues as well - my 40% C was 72 last time i measured)

So - Im aware that the paper is a factor, with distortion, and water uptake due to the old style dampers. Also the tack of the ink perhaps?

I had the idea of repacking the last unit plate cylinder to .2 under, and packing the blanket to the corresponding .2 over. Is this likely to effect a change?
The other option is to overpack the cyan and magenta - but with the gain issues i really dont want to do that.

Any ideas or suggestions much appreciated.

 

[cjwworld]

I am having the same issues.. Usually the first color and second (C&M) is 'longer than the rest. I am interested in responses also

 

[rbailleu]

You can try the plate thing. if that works I would pack the impression cylinder for a permanent solution. dealing with plate packing would be a pain in the neck.

 

[cjwworld]

You can try the plate thing. if that works I would pack the impression cylinder for a permanent solution. dealing with plate packing would be a pain in the neck.

are talking about the blanket cylinder packing?

all the color units have the same guage

 

[Deleted member 16349]

Hi all, im having a few quality control issues on the press.
I always have large inconsistencies in print length, which manifests itself at the last print unit.
I have the colour order C-M-Y-K. This is due to the type of work we do, it means 50% less washups.
The plates are still manually made, from film created on site.

By the timei lay down the black, its frequently 1mm or more too long. So i reduce the plate tension, (slacken bolts) to get it to fit, however it seldom does, and reversings look fuzzed.

The press is an older stlye Speedmaster 102. Conventional damping. I have calibrated the packings to 0.05 squeeze. (dot gain issues as well - my 40% C was 72 last time i measured)

So - Im aware that the paper is a factor, with distortion, and water uptake due to the old style dampers. Also the tack of the ink perhaps?

I had the idea of repacking the last unit plate cylinder to .2 under, and packing the blanket to the corresponding .2 over. Is this likely to effect a change?
The other option is to overpack the cyan and magenta - but with the gain issues i really dont want to do that.

Any ideas or suggestions much appreciated.

Is it possible that you don't have a matching set of blankets in the press?

Different types or even different batches of blankets can cause variation in the pull on the paper.

 

[GazKL440]

slight overpacking k blanket should help a little, have a look at gripper pressures on offending unit and perhaps back off impression to minimal printable pressure on all units may help if not already done..

does the image improve with temperature or on the run or do you have to split difference and bear with it?

 

[rbailleu]

changing blanket packing is not the answer. you must change the plate or the impression cylinder. the best is the impression cylinder. .002 under the imp cyl jacket should prove very effective. run a sheet of 80# text and 10pt cover and measure the difference in form length. the only difference is the circumference of the impression cylinder changes with the thicker paper on top of it.

 

[spigot]

Thanks for the replies guys

Blankets are the same. Caliper doesnt change, and alot of the time ill change them all for a new job if its a long one. and put the oldies away for offset or bond paper jobs.

I just have to split the difference all the time. Which is a pain because everything is 1-up A1 so most sigs have a few dodgy pages here and there.

I cant alter the packing under the Impression Cylinders, because they are the Refined cylinder jackets for perfecting, and theyll be ruined if removed.

I understand that its preferable to alter the plate packing first, however the press has .4mm permanent packings stuck to the plate cyls. So to shorten the image i would need to lessen this, but raise the blanket to keep it in spec. Or am i wrong here...?

Print pressures are always minimum. There could be a heat issue there, as its single shift, but i dont really notice how much the length varies, so i will keep an eye on this.

Its also alot worse on thinner caliper stock, 115 gsm paper is all over the shop,but 170 gsm is almost in register.
Today i had the Cyan printing wider than the M-Y-K, by around .75 to 1mm.

I really dont know what the hecks going on!!
I think the answers may be at the pub......

 

[nhprinter]

Hi Spigot,

You need to INCREASE the packing behind the plate to shorten the image. .002 should do it. There's no need to change any of the other packing for this amount. (the sheet that is in between your plates in the original package is .002)

Keep in mind...this will only effect the fit from gripper to tail, not side to side.

Dave

 

[cjwworld]

I will try the suggestions, guys for me.. Thanks

 

[SpeedKing]

hi,i noticed you said that the impression jackets were refined jackets for perfecting? are you aware that the jackets for CMYK perfecting have a different caliper for each unit? for example on a ten colour press unit6 (black) is thinner or thicker than say unit9? (yellow) i cant remember which way it goes but i am sure of this as each jacket has number on it telling you what caliper it is.

 

[spigot]

the jackets on the press are the same. Its a 2/2 102 speedmaster, so i had refined jackets put on 3 and 4 as the other ones were nearly falling off with cracks and wear.

Ill try and adjust the packings on the black unit, see if that helps. I dont really want to change anyth of the other units, was kind of hoping for a fix of the black last unit only.

Thanks for the suggestions, it looks like i may just have to live with it, until the prepress gets upgraded to CTP and or a new press magically appears. Which will happen right after i win the lottery. Without a ticket.

cheers!

 

[rbailleu]

is the growth worse on the first side or second side.

 

[otherthoughts]

Bearer to bearer contact?

Bearer to bearer contact?

This testing pertains only to presses that are designed by the manufacturer to run in bearer to bearer contact, and as far as I know likely only applies to sheetfed offset. The pressman should know which is the case for his press.

That said, a quick(5 minutes) and easy method to ascertain whether or not the plate and blanket cylinders are still running in bearer to bearer contact.

Only one inking unit should be tested at a time.

• Stop the press
• Clean the plate and blanket cylinder bearer surfaces on both ends of the cylinders and all the way around the cylinders.
• Place your standard-test-thumb on the ink-form roller to ink your thumb up.
• Transfer your thumb-prints to the bearers of the plate cylinder on the drive and operator sides. Inch the press as needed to apply about three or four thumb-prints evenly spaced around the plate cylinder's bearer's. What you want are crisp and clean prints suitable for law enforcement use
• Lock-up your ink form rollers so that they will not be applied to the plate during the forthcoming impression-on state
• Inch the press so that the plate and blanket cylinders face one another at their tailing edge's(just before reaching their gap's)
• Trip the impression-on/plate-mounting switch for the unit you are testing
• Inch the press through one complete revolution of the impression-on cycle in a single continuous nonstop motion.
• What you want is one single revolution of the plate and blanket cylinders with impression-on, beginning and ending with the cylinders at their gaps in a single uninterrupted inch of the press.

The thumb-prints you placed upon the plate cylinder's bearer's should now have been transfered to the blanket cylinder's bearer's. The thumb-prints on the blanket cylinder's bearer's should be just as crisp and clean as the originals on the plate cylinder. Anything such as, missing prints, smudges, smears, etc. indicates that the unit's bearer to bearer mechanical settings are less than ideal and should be looked into by a press mechanic.

In conclusion, if your press is designed to run with bearer to bearer contact between the plate and blanket cylinders, and for one reason or another it isn't. Then any changes you make regarding the packing of such cylinders should not be considered reliable as a consequence.

For what it's worth.
otherthoughts

 

[spigot]

is the growth worse on the first side or second side.

hope i understand your question
I work and turn all the 2 sided CMYK jobs.
For perfecting its not really an issue because 9 jobs out of 10 are offset and have small bleeds, or arent as quality critical.
And when it comes to the backing up, the problem remains, although i cant say for sure if its better/same/worse.

 

[Sfdp2300]

Seems like this is a regular Heidi issue!
I also run an older model speedmaster 102 and we get the same problems as you mention. When we have tight register such as knockouts and 1 unit is printing longer than the others we will add packing to the plate. (We do not have to do this on all jobs)
Keep in mind to shorten image you add to the plate and take away from the blanket.
as for the image width being wider on 1 unit from the other , Well we are still working on it only realy see that on 38" sheets to 40" sheets.

You say older model Heidelberg what year are you talking?

 

[Alois Senefelder]

"Enlighten"

"Enlighten"

Hello all,

"From knowledge to competence it is a great step ----- from ignorance to competance an even greater one" (General Hans von Seeckt)

Now some PDFs for you to read !! --- re "Print Length"


regards, Alois

 

[madjock]

If your image is printing too long you need to add packing under the plate to increase the circumferential speed and make it print shorter, I have in the past, stuck a sheet of tissue, the interleaf sheets from the plates, to the back of the plate, and this works just fine, I believe the ratio of decrease is about 5:1.

 

[spigot]

You say older model Heidelberg what year are you talking?

ummmm.... 1981

 

[SpeedKing]

the age of the press is not always an issue,these things last for years,tissue behind the plate is the quickest and easiest option.