GTO 52 Swing Arm

[ron]

We have a 1990 GTO 52 that has had a problem for some time and no one has been able to fix it, myself or Technicians.
When we change the speed the image on the sheet moves forward or backwards, depending on speeding up or slowing down.
It registers perfectly at a set speed ( 4 col ).
There is no dot slur when you change the speed only the grip margin alters.
I am open for any advice on this problem.
Thanks
Ron

[junker1984]

Hi Ron - All four units in unison? No angle to the image on the sheet? Could be something as simple as worn out traveling feed grippers or the sheet drop adjustment, which is where the traveling feed grippers release the sheet to the headstops. Too early, and the sheet is thrown at the headstops, too late and the sheet is slammed into the headstops, both cases would be overall sheet to sheet misregister, but the misregister wouldn't be consistent. More info would help. Good luck Steve

[ron]

Sorry, GTO 52 single col. the reference to 4 col was that we do four colour one col at a time and the registration is perfect as long as we do not adjust the speed from start to finish.
The Techs have checked gripper timing and clearances on the swing arm, impression cylinder, front lays and transport grippers all have been correct or a minor adjustment was performed but still the problem exists.
There is no damage or marking of the sheets front edge.
The machine has done only 22 million impressions, cleaned and well maintained since we got it about 8 years ago.
Never had a smash or bent anything since we had it.
Have been running GTO's since 1978 and this one still baffles me.
Ron

[junker1984]

Ron - Does the register vary from sheet to sheet? Does thicker stock run better than lighter stocks? Is the problem intermittent? Does coverage affect the problem?

[ron]

There is no variation, no diference from NCR to heavy artboard.
Every job no exceptions, have never noticed any difference with coverage or ink tack.
Some time ago we ran a full halftone with a 20% dot, ran about 100 sheets through twice at 6000/H with no change.
Same again but the second run was 6500/H and the reistration had moved 2 row of dots evenly around the cylinder.
No difference with blanket and packing change, we also have a bearer hight gauge so the packing is always to spec.
Interesting!
Ron

[junker1984]

Ron - Given the info you've supplied, I would first question the condition of the alignment pin in the plate cylinder double gear configuration. On the face of the outer gear (the one with the round reliefs you put your T-handle 10mm allen wrench through to swing the cylinder for coarse positioning) you'll see a flanged pin held in place by 4 6mm (5mm allen cap) bolts. If this is removed and you see a lot of rust and galling on the pin surface, it will cause serious (but slight) inconsistencies in circumferential register, mainly after makeready and speed changes. Good Luck Steve

[ron]

I will check this tomorrow.
Also there is no image doubling or dot slur when we speed up or slow down the press.
Thanks
Ron

[John]

Hello Ron, Your Swing Gripper has a Torsion Spring in the shaft that the Swing Gripper is mounted to. I have seen where people have worked on the machine and did not set it tight enough, at higher speeds this caused the register to jump , because the bar was not able to return to its resting point for registration fast enough. If this seems to be the case, tighten up the torsion spring and see if this makes a difference............

[ron]

Can you give me a brief outline on how to do this.
Which side ect.
Ron

[John]

Hey Ron, Please keep in mind this is a first guess over the internet. Go to your parts book, pages 12- 2 and 13-1 ( the wire thing is the torsion spring ). Now remove the cover on the operator side. You will see a chain that pulls on a lever this is what makes your swing gripper swing. At the end of the swing gripper shaft, where one end of the chain is connected you'll see that the piece clamps on to the end of the shaft. Under the clamp piece is where the torsion spring is, going through the shaft. Mark all the parts positions, Release the spring tension and take it a part, slowly,also check for rust.......