printlength issues. constantly.
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.
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
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?
Originally Posted by rbailleu
all the color units have the same guage
Is it possible that you don't have a matching set of blankets in the press?
Originally Posted by spigot
Different types or even different batches of blankets can cause variation in the pull on the paper.
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?
Just get on with it. Its as simple as that.
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.
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......
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.
I will try the suggestions, guys for me.. Thanks