packing and impression

good morning. Just another question about clutch problems on a GT Heidelberg Windmill press. I was wandering if too much packing and to much impression can cause premature wear on the clutch ring. I found out the other day that they were running 6 pieces of packing for die cutting. Wich I thought the max. was 3. Thanks for your help.

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You do not state the caliper of your packing sheets. Are you using paper or board?

The rules for the amount of packing on any Heidelberg platen are the same whether printing or die-cutting!

If the impression is heavier at the bottom of the forme then there is too much packing; if heavier at the top of the forme then there is too little.

The state of the packing will have no effect on the life of the clutch ring; premature wear is usually caused by a poorly adjusted clutch.

If the machine is running smoothly: ie the upward motion of the platen is at the same speed as the downward motion then the clutch is working properly; any variation in this indicates a slipping clutch, and adjustment is needed.

Fifty plus years of hands-on experience with all forms of Heidelberg letterpress, and I have never had to replace a clutch ring.

They are using paper. Im not on site there. I just no the last time I visited that there machines seemed to be slipping when feeding sheets and die cutting. I cleaned all the excess oil from the fly wheel. There adjustments are maxed out so it seems like its time for a new clutch ring. I do know that they had excessive packing and impression when I talked to them on the phone. I just want to get to the bottom of this before installing new ones and have the same thing happen. I think its lack of training on a die make ready. I know they are original clutches both machines are early 1950s. Thanks again if you have any advice.

Look in you operator’s manual. There is a page on clutch adjustment. You need a wrench and a screwdriver and about 10 minutes. Contact me if you have questions.

“I found out the other day that they were running 6 pieces of packing for die cutting.”

Good Morning! If your buds are trying to die cut on tympan paper, no amount of clutch adjustment or packing is going to help.

Die cutting is usually done on a GT against a steel jacket, or a steel plate mounted to the tympan. Packing with Mylar is done under the die cutting form, with strips of stainless steel tape behind the form for low spots. Mylar is best in thin (0.006”) sheets, because it conforms, as opposed to aluminum sheets (i.e. small press plates) that stress and separate.

As Mr. Bennett pointed out, a stronger impression at the bottom of the form necessitates removal of packing behind the form. Conversely, a weak impression at the bottom of the form indicates more packing is needed behind the form. If packing is added, impression should be backed off, and only gradually increased.

In no case should you pack beneath the stainless steel jacket, or the steel plate on the tympan of a Heidelberg GT. The windmill arms will scrape and gouge anything more than 0.040”, or 1/25th of an inch higher than the bare tympan! Pack behind the form, carefully, and apply no more impression than is necessary to achieve the “Snap” that indicates a good clean cut against the steel jacket.

Sorry Jim to disagree with your view on packing adjustment behind the forme.

This is not the case; the adjustment to get an overall level impression is dependent on the thickness of the packing on the platen. it’s like a clam shell, the more you increase by turning the impression screw, the further the top of the platen moves compared to the bottom of the platen.

When die cutting, yes, any low spots should be raised by packing behind the forme

Thanks for all the valuable information. My point I was trying to get across was this. They are die cutting using excesive pressure for impression, excessive packing. I think 3 sheets of packing is max. Im thinking its making the machine work extra hard, thus wear and tear on the clutch ring. I know they are maxed out on there adjustments. So, I have turned 2 clutch rings down, because you cant buy original size rings from heidelberg anymore. And will go and install on Monday. Just was looking for more troubleshooting advice. Thanks again