Heidelberg cylinder diecutter

Can someone maybe help me.
I have a Heidelberg Cylinder diecutter.
Height knife & crease rule ok.
If I put a horizontal knive in the front and one horizontal knife in the back, the cut length is different then the printed sheet I want to diecut by at least 1.5mm.
I printed a 6 pager that I needed to cut and crease at the same time, couldn’t get the ordered knife to cut the same length as the print.
Why is that or what am I doing wrong.
Thanks for your help

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if your press has a sheet brush on the cylinder, use it. on your bed, the die set, fill the whole void between rules with foam. under carpet padding foam can work..
feed a sheet into the gripper. check for pulling out, then feed another sheet into the gripper, mark around each gripper finger with a pen and turn the press thru to the point where the delivery gripper is just about to pick the sheet from the cylinder gripper. look in with a brite light to see if the sheet has slipped out of the cyl grip at all.

If I understood correctly, you have a cutting knife in the front and a cutting knife in the back and in the middle between both there is a creasing knife.

If that is the case, and you said your creasing and cutting knives are the same height, I would check to see if when you’re tightening the set up there is arching especially if your furniture is wood, that seems to have happened with me before. In that case the creasing knife is hitting the paper on the cylinder before the second knife reaches and thus is “squeezing” the paper inside the matrix shortening it from the back side.

Can’t you compensate that 1.5mm by adding a slice of thick paper in between the furniture? Or is it varying in between prints?

I would get a sheet and draw lines of where the crease and two cuts should be before running it in the machine and that way you can maybe tell which knife is the problem, if it’s the first middle or last one.

In case the knives turn out not to be the same height, I would suggest you add a sheet of paper underneath the ones that are lower under the chase, that way you compensate for the height if you don’t want to get new ones.

I hope this helps at all.

Shadi Ayoub

didn’t read the part about the horizontal knives. those are a problem on a cylinder. you don’t say if this is a rerun or not.
most times, like with a pocket folder, many will pull out the top, head, trim to die cut the rest, then power cut, using the pocket edge into back guage. need about 3/8” for gripper. some presses will go a little less, but old cylinders have their own personalities.

It sounds rather like a made up die-board, tell me if I’m wrong about that. If it is a made up board, and the cut to cut dimensions are the same as the printed sheet (No changes from humidity/temperature/etc) then I would presume that the knives are cutting long because the sheet is sagging between the knife and the crease.

If you are not using matrix rule and don’t have ejection rubber at the crease, the sheet will bow down into the voids od the form (hence Ericm’s good advice of filling in the form).

It is also entirely possible that you are having problems with air trapped in the form, but that generally manifests itself as wrinkles.

Eric I believe is on the right track, you have got to hold the sheet to the cylinder with the cylinder brush and you have to fill all voids in your form with foam rubber or ejection rubber, Eric knows his stuff. Bud

Good info so far, not sure if this will help. If you are cutting a printed sheet make sure the printed sheet image is true to size. As printing blankets wear they can get a different circumference value leading to a change in true absolute position as will paper stretch. It sound like this is a made die and not set rule or you could shim the position. One of the guys above will tell if this will work or not but a thin sheet of packing under the jacket will change the circumference of the cylinder and may fix the issue.