Original Heidelberg Cylinder impression backing off

HI all,
We have a Heidelberg Cylinder press that is used for diecutting, and the operator is having problems where the lever is moving towards the left during the run. So far his solution is to use a wooden wedge or a bungy cord to keep it on impression. Anyone run into this problems?

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Check to see if the knife height is correct. Should be .918 check to see if score height is correct.

our knife height is .923” and the score is .895”. does “light form - heavy form” lever make a difference for diecutting?

Your knife height it wrong. If the score is .895 the knife should be .918

Still check and make sure your die maker put in the correct knife height. They have been known to put in .937

Unspecified (as yet) but is it possible to state IF the machine in question, is still equipped for All Up letterpress printing or is it dedicated, for cutting creasing only.??
May have a bearing on Cutting Rule height, plus the possibility of the >Bed< being Ground Out, again influencing the Cutting rule height, surely the Die Makers would ask this question.?

If you think the cutting rule is .005 too high then take .005 of the packing out from under the die jacket. For the experts above .923 or .927 cut is used on cylinders by the more skilled operators who know how to properly pack the cylinder and understand surface speed.
Note The most common diecut rule height in North America is .937 for Bobst and Thomson style equipment. Because much die cutting is performed via letterpress .918 is available as the 2nd most common cut rule.

Thanks for all the info,
its seems all the die we have are .923, I believe the cylinder jacket is packed to 1.2mm. I’ll suggest adjusting the packing. We have some other issue and I’m trying to get the mechanic in to fix them.

.923 is standard for many shops(somebody knew what they were doing) just remove some packing. Your real problem is likely elsewhere
.918 type is for putting an image on the surface of stock with ink but when die cutting you must penetrate the stock so do the math required to keep the surface speed of the die and the stock the same. If done correctly cut products will be correct size and you will need less die nicking.

check that the 2 mechanical cutout devises are set correctly.

Against the original query/question, the Maths involved, i.e. the thickness of the Cutting Jacket (even at thinnest available can You even GUESStimate?) + the stated packing, under the jacket, + the stated Height of of the cutting rules, A + B + C, would seem to be adding up to potential problems, maybe responsible for the impression lever, fighting to escape >Danger< Bungy & Wedge,???

Is the Jacket crucified already.???

From the words of a Very, Very, longstanding H/berg Cylinder operator, it is frequently required, when commencing a new run for Cutting to have to literally hold the handle on Full Impression for the first 10 - 15 impressions, has or can Your Minder try this before reverting to, Wedge & Bungy.

Apologies for potential rubbish, but may prompt Good info.

My cylinder is an original KSBA it requires a total of 1.2mm or.047 on the cylinder including the stock to print when using .918 type(this is normal) to die cut with .918 you need .047 on the cylinder including the die jacket but excluding the stock to cut. My jacket is .031 and if using .918 cut rule I put .016 under the jacket. If using .927 cut rule then .006 under the jacket. .923 is probably the dream cut height, the problem is the availability of perf rule in .923 or .927.
You should never have to beat the crap out of a press to die cut.

Hmmm, not much discussion of the “why” of why the higher rule is ideal. Is this because you want the intersection of the cutting rule and the paper surface to be at the exact height of the bearer?

I can see where underpacking would slow the sheet, just as overpacking will accelerate it (and generally lead to slur at the tail of the sheet).

Is there a reference to the physics of cylinder die-cutting? I would like to find out more about this.

mikefrommontana you are on the right track this is all about surface and below surface speed. I learned about this years ago when making dies for the better die cutters in Toronto. Further enhanced by subscribing to expensive but worth it trade journals.
When a cylinder has had the bed ground to accept .937 cut rule then you are able to use the wide variety of rules that are available to the diecutting industry and not just the few selections available in .918

Here’s why If you die cut with .918 on a cylinder the sheet will be going faster than the die so your finished product will be bigger than the die. Most printers that dabble in die cutting don’t need to know this stuff. However if you are locking up rules and have a micrometer compare the difference between what you lock up and what you actually do.

link gets you on to Kevin Carey if you are interested.