Bouncy bouncy bouncy
I’m having a devil of a time with paper bouncing off the side guide of my Heidelberg Windmill. It’s not consistently doing it, but every few prints. It just did it on jobs I ran on Colorplan 220 lb. and Crane’s 179 lb. sheets. I seem to have stopped it with the ol’ flying dutchman technique, but I’d like to get to the root of the issue. I’ve tried running the press fast, running reeeaaaalllly slow and it continues to do it. The worst is that there’s no way to tell until you go to put down the second color in register and suddenly find half the prints are off. I have the side guide all the way out. Previously, I’ve tried the guide further in, but it tends to mark the heavier papers, so I just leave it out.
Any thoughts?
try the side guide closer to the middle of the adjustment, too close to the platen and the sheet will bounce off it.i always run my windmills really slow.
I have it as far out as it’ll go and it’s bouncing. Does moving it in some lessen the amount of gliding it does after the gripper releases it?
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Couple of (maybe) silly tricks, wipe your Tympan (top sheet) down with Anti-Static solution, as used by serious Hi-Fi VINYL record collectors, you must have a few left Stateside, and Suppliers.?
And/Or wipe the Tympan down with Silicone based polish, both the above, used with some success on small Litho machines, when the braided Copper Anti static conductor was not available
Which was not very often because the Fine copper screening from low loss Television cable turned in well, A. as a trailing anti-static and support on the feeder plate and B. ditto on the delivery, conducted the sheets down flat, especially when the Pen Steel guide was A.W.O.L.
Apologies for rubbish, but may provoke more Scientific result,s.??
If it is being pushed rightward into the guide and bouncing back left, I’d try a bit of post-it double side tape in the trough of the lower guides to add friction against the edge of the stock.
I’d also ensure the stock is gripped squarely and not rocking when dropping into the guides.
WRT no way to tell before the second color: do you have the handy Align-Mate? Inconsistency can usually be seen with the grid.
We are also presuming the stock is bang-on.
One technique I learned when running a large sheetfed litho press, and have utilized on my letterpress presses when register is critical, is to put a 1pt. rule at the expected sheet edge. When printed, the mark will carry down the edge of the sheets in the delivery, and you will be able to see immediately when the register is out beyond the 1pt. +/-. Of course, this will not be useful of your stock is being printed at final size (no trim).
John Henry
I have something like an align-mate, but the bouncing is inconsistent, so it’s hard to tell. I might run off 30 prints with no bounce, then it’ll bounce every few prints for the next 30.
I’ll try the double-stick tape on the guides and see if that helps as well.
How can you tell how the sheet is dropping into the guides? Usually it’s almost completely closed at that point and I can’t see anything.
are you using brass or nickel guides, I always use brass guides, the nickel guides give me a hard time.
Brass. I used to have a devil of a time with the nickel guides (sheets kept dropping below the guide) so I switched to brass and haven’t looked back.
Something similar has come up before
http://www.briarpress.org/37801
Check also if you have a bent gripper, see if both grippers take the same amount of bite on the stock as they pick up.
Check your gripper timing, take the cover off the front and check the cams, should be a gap of about 2/3 thou if I remember rightly.