Misregistration GTO52

[mantman]

I think this is an issue asked one too many times but i will ask it myself...why i have registration issues -GTO 52 1 color.-, 5-10 sheets good 1 or 2 misregister by 0.2mm skewed.
Some thoughts:

As far as i know and read by the book, i set up side lay for 2 sheets with sheet smoothers/brushes middle of sheet/envelope etc.
-Feeder table is well not totally straight since i tampered with it OS side. -meaning OS is 0.5mm and DS 0.45mm-
-Feeder grippers are new and leave substrate correctly -they open at the same time just before front guides and with 1mm distance drop-.
-Not sure at all about front guides condition -hopefully not bent-
-Side lay is set with 2 substrates between table
-Grippers at impression cylinder some grip 3mm some 4,5mm. What is the min/max gripper bite 4mm and 5mm? and tension of grippers or bite and how to set them -i think a filler of 0.03 is needed?-

Thank you in advance

 

[Travis Young]

My thoughts:
1) Don't overthink it. Normally something simple.

Dot to dot rego is easier to obtain with a lower press speed.
My best results are obtained at around the 4000 mark.

Wind off the double sheet detector. Eliminates a variable.
Also ensure the bottom bit of the double sheet detector isn't sitting proud of the feed board. Screw down with a small flat blade screwdriver if necessary.

Side lay height is better high than low. If in doubt wind it up a little bit higher.

A spotlessly clean feed table looks good but can be more susceptible to static than one with a bit of dust/powder spray on it.

Normally I find the amount of pressure applied by the slow down brushes has the biggest impact.
PARTICULARLY IF THE SHEET IS SKEWING IN THE FRONT LAYS.
It also helps if the brushes are in new condition. I like to run two of them at the back of the sheet roughly in line with the front lays that are in use.

On a 52 using an A3 or larger sheet I run 5 sheet smoothers and I don't use the metal sheet brake for dot to dot registration (it's handy for less crucial high speed work but a hindrance for perfect rego in my opinion).

Not very often that shops run multi colored jobs on a single colour press these days, especially with tight fit.
A dieing art within a dieing trade.
Hope it goes well.

 

[mantman]

Thank you for thoughts Travis!

-I am quite certain double sheet detector is not an issue -usually if it holds sheet/envelope it usually wrinkles sheet-
-As for sidelay i wind it up a bit higher if i see sheet coming down wobbly or push motion of sheet is unstable.
-I believe static is easier with powder dust table than clean one, cause of traction of sheet with dust.
-I agree with you about brushes, but i check them up if they are tight on sheet. Sheet brakes are important for all speeds -along with brushes- so sheet doesnt bounce away from front lays, unless you have really small size of substrate. By the book the alignment is middle of sheet and i use 3 smoothers -one mid and two 10cm away from side lay-

-I tried putting one narrow sheet of 0.05mm thickness from plates and pulled them from swing grippers and came out tight without tearing.

-What i did notice today is that swing gripper closes a bit earlier OS than DS. Could it be that these 2 grippers are clogged with ink/water?-will flush them with nitro solvent/wd-40- unless the culprit is front lay bar.
How to check them by hand -what position of swing-?

 

[junker1984]

Bring the swing gripper bar up to the point you see the grippers close on pad (no plus or minus degree values, visual is good enough) and use a small bladed, long shanked screwdriver to push the grippers open. If you find any that don't open, or don't return to the pad under their own spring load, then you must free them up. It can be a chore, just keep in mind you may be dealing not only with dried ink film, but also etch. If penetrant is not working to free up the grippers, assume that you may need to soften up a build-up of dried etch. In this case, hot water is the answer...need I mention that if you use hot water, that you must then lube everything up very well? Didn't think so. Only then would you consider rough checking the gripper settings by feeding .1mm strips into the grippers and slowly crank forward to see how consistent the closing times are. Process for multicolor machines is a bit different but principally the same.

 

[Colour Master]

Only use two headstops on the sheet. Pull them back about halfway. Use minimum push on the side guide and make sure leading edge of sheet isn't catching a headstop. Minimum pressure on all smoothers. You should have dead on regester at any speed.