thick stock on a windmill

I have a question regarding printing thick stock on a windmill: Today I tested printing thicker, laminated stock, 2x300g and 3x300g papers — the grippers and paper transport in general are working fine, but I have another problem:
The paper hits the corner/edge of the platen when the gripper swings over the platen (I only had a tympan without any packing on it) and rubs over the corner. The platen corner leaves marks on the paper which are very light but multiply when printing more colors.

Do you have an idea how to get around this problem? Do you have experience with silicone spray or teflon spray?
I would appreciate any suggestions.

polychroma

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Well, sometimes I’ve been able to reduce this marking by doing one or both of the following:—

1. Run a strip of 2” cellophane packing tape down the left
edge of the platen against the chromed plate that fans out to the left, and the tympan or jacket.

2. Try to lift the arm off the packing slightly with a strip of creasing matrix adhered along the top edge of the packing. Be sure not to extend it too far to the right so that it doesn’t catch the edge of the sheet on delivery; same for feed—make sure the edge of the sheet isn’t peeling up the matrix.

Sometimes I have not been able to solve this problem.

Brian

Had similar problem printing on the back of framing mattboard. Solved the burnish mark by attaching cloth or nylon to upper left corner of platen and the chrome guard.

Polychroma,

Are your marks on the edge of the sheet or the back?

Glenn

That’s a good question Glenn-

If it is the edge of the sheet, I have found that it’s not the platen that’s nicking the stock, it’s the left side guide.

The trouble with heavy stock is the tail of it does not have enough time to lift up over the guide before the gripper takes it from the feed table.

I use two tricks that have worked for me:

1. Pivot the back end of the left side guide out so that it is around .25” away from the stock, but the front of the guide is still in place and still helping the registration.

2. Use a plastic wedge (like a door stopper) to lift up the tail of the sheet on the feed table. You’ll have to adjust your sucker tilt and table height accordingly. You’ll see, though, if you try and lift it too high and create too much angle, you may have just created a whole new set of problems. Start with lifting the stock just a little, and see how it goes.

Hope this helps-

Tony