3044Re: [PPLetterpress] Windmill Registration Problem
- Oct 4, 2004Every-other-sheet misregistration is a common scenario. When I can't fix something by adjusting this or that, I go back to Square One, so to speak, by running a sheet through in slow motion. That is, I turn on the press, and have the sucker bar pick up a sheet and let the gripper bar grab it. Stop the press right at the point where the gripper bar has grabbed the sheet, but before it has started to swing in to the platen. Now shut off the motor and let the flywheel stop spinning. Now you can open the hatch on the flywheel's safety cover, engage the clutch, and start turning the press by hand. Watch the sheet carefully as it is being brought in to the side guides, and look for places where the sheet is getting hung up or misaligned. What I would look for is:
Is the sheet too close to/too far from the bottom guides?
Is one end of the sheet slipping off the bottom guide?
Are the bottom guides aligned well with the bottom of the platen?
Does the front of the sheet get pulled against the front guide before the gripper releases it, or is it released just a little in front of that guide?
Does each gripper arm grab the same amount of paper, or is there a big difference? This would indicate that one arm is way out of alignment.
Because you are getting crookedness, I would suspect that one end of the sheet isn't landing on the side guide, and maybe is slipping between the guide and the platen. There is a little widget that slides onto the track under the bottom edge of the platen that is made for this kind of situation- it keeps the sheet a little off the platen until the side guides are up and in position. Alternatively, you can cut a little triangle flap in the tympan and curl the point up a bit, at the end where the sheet is slipping down. This pushes it off the platen just enough to catch the side guide.
Good luck with this. These things can be really frustrating and each windmill has it's peculiarities, in my experience. But you can figure out a lot when you turn it by hand and look at what is going on carefully. It may not be the gripper arms causing your problem, in the end. Cast out all preconceptions and put your trust in empirical observation!! ;^)
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