Thursday, July 24, 2008

Skip Feeding

We thought we would expand on our recent post about achieving solid areas of ink. One thing that we've found to work well on some recent jobs is skip feeding.

This is a way to accomplish "double rolling" of the form on the Heidelberg windmill.

Skip feeding allows two (or more) passes of the rollers, which works very well for eliminating ghosting and maximizing coverage. It requires quick, constant two-handed operation of the feed and impression with each sheet, and so is only really practical for short runs of special items. If you're running a few thousand of something, you probably want to figure out how to make it work with the rider roller—unless you really enjoy working out one arm and hunching over. (This is one thing that is more easily accomplished on a hand-fed press such as a C&P where you only move the throwoff lever on and off, as feeding is at your manual control. You simply pause and let the press cycle once more, while having a leisurely interval to ready the next sheet.)

After a sheet is picked up, the suction trip is pushed in (turning off the paper feed) and the impression lever is pulled on. After the impression, the lever is pushed in (impression off) and the suction trip is pulled out (feed on.) The key is to develop a rhythm, and the machine makes plenty of sounds you can synchronize yourself with. I pull the impression knob out as soon as the paper is pulled from the suckers by the gripper. The impression lever needs to get all the way out and down in its "notch" before the press closes fully. The following video shows a pretty slow pace for demonstration purposes.

On YouTube:

On Vimeo (high quality and downloadable):

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