Die-Cutting Question - Heidelberg Windmill

Discussion in 'Heidelberg Printing Presses' started by holmburgers, Apr 24, 2020.

  1. holmburgers

    holmburgers New Member

    Joined:
    Apr 2020
    Messages:
    3
    Location:
    Vienna, Austria
    Hello All,

    I have a question about die-cutting on a Heidelberg windmill-style press, and I'm hoping to get some input from the fine folks here on this forum.

    We are cutting out rectangles of very thin 'glassine' paper (42gsm/~12lbs), to which strips of double-sided tape have been applied prior to die-cutting. The tape is not covering the entire surface, just strips in the necessary areas. Therefore, the dies are cutting through areas where there is tape, as well as areas where it is just the paper. I have attached 3 images; 1 showing the prepped blank and the die, and 2 showing the finished parts. Notice, the smaller part has a very important perforation.

    This is an extremely efficient way to produce these parts for us, since in the finished state they are completely ready for assembly. Frankly, I cannot conceive of another way to produce these without die-cutting, or significantly slowing down our assembly process.

    Our printing tech (who admittedly has limited die-cutting experience) has expressed concern that because of the differential thickness of the part we are cutting, it is potentially going to damage our Heidelberg. It has been noted that the required pressure to cut this part is quite high, and the thinness of the paper does not help.

    Would you agree that this is damaging for the machine? If so, why? Also, what part(s) of the machine would this damage if we continue operating in this manner? What solutions would you recommend?

    We are a scrappy little group making an instant-film product, and producing everything in a small workshop here in Vienna, Austria. We've been using our Heidelberg to die-cut nearly every part of our product, but this one in particular is quite tricky. I would love to avoid having to come up with a new procedure, and I'm hoping a little expert input will help us make a more informed decision about how to proceed.

    Will be happy to clarify and answer any questions.

    Many thanks!

    Chris
     

    Attached Files:

  2. mantman

    mantman Senior Member

    Joined:
    Nov 2015
    Messages:
    184
    Location:
    Greece
    More likely to damage cutting jacket than machine itself. You can always add pressure with thin strips of paper/tape behind whole die form or specifically at cutting dies. There is a shim tape made of metal with different thickness -0.03 to 0.10mm- that you can use.
     
  3. Travis Young

    Travis Young Member

    Joined:
    Oct 2019
    Messages:
    66
    Location:
    Victoria Australia
    More experienced members please correct me if I'm wrong but platens have a shear pin don't they? So besides from damaging the jacket (who cares) the pin is deliberately made to be the first point of failure?
     
  4. NotAGooner

    NotAGooner Senior Member

    Joined:
    Dec 2007
    Messages:
    266
    Location:
    UK
    Travis, yes indeed they do but I think it's a collar rather than a pin? Very long time since I ran one of those. :)
     
  5. holmburgers

    holmburgers New Member

    Joined:
    Apr 2020
    Messages:
    3
    Location:
    Vienna, Austria
    Hi guys, I very much appreciate the comments. I'm a total noob here... what is a shear pin/collar? At any rate, it sounds like maybe my printing colleague is unnecessarily concerned?

    I will also mention that on the back of the die, he has applied copious amounts of CITO shim tape. To my eye, it seems excessive, and if someone could point me towards a resource for proper shimming technique, I'd owe them a very expensive glass of beer... ;-)
     
  6. Travis Young

    Travis Young Member

    Joined:
    Oct 2019
    Messages:
    66
    Location:
    Victoria Australia
    A shear pin or collar is a deliberate weak point on a machine so that if you smash the machine the only thing you damage is the pin or collar.
    It would pay to have a spare on hand anyway.
    They're pretty tough old machines. I can remember back at trade school hearing them knock from having the pressure up too high. If hundreds of apprentices can abuse them year after year I would say you should be ok to keep going as is.

    Your colleague sounds like a good operator. Doesn't pretend to have knowledge that's not there and exercises due caution.
     
  7. holmburgers

    holmburgers New Member

    Joined:
    Apr 2020
    Messages:
    3
    Location:
    Vienna, Austria
    Thanks Travis. You're right; he is a good operator and does a great job with both printing and die-cutting.

    I appreciate getting a sense of these machines, and indeed, it sounds like they're workhorses that should be able to handle some rough riding. I'm not sure if the knock you describe is the same, but I believe with very high pressures our operator has observed a brief "stall"(?) as it presses and releases. I believe this was getting him worried.

    Regarding the shimming tape that is being used on the back of our dies, this has been used to chase inconsistencies in planeness and to allow for even cuts across the entire platen. However, with this tricky part, there is a constant game of cat and mouse, and our operator has complained that every time he goes to cut this part, he has to adjust the shims in order to get it right.

    I honestly believe that if the shimming technique could be refined here, the other concerns and problems would go away, as it should (?) allow for the use of lower pressures. Any advice on this point would be most welcome, or even a referral to a classic text on the subject would be amazing.

    I have asked the CITO company as well and hope to hear back from them.
     
  8. biggles1

    biggles1 New Member

    Joined:
    Dec 2015
    Messages:
    3
    Location:
    peterborough UK
    From what you’ve said, you shouldn’t have to use any shimming..are you running the sheets “tape side up”?. The thickness you’ve stated shouldn’t pose any problems. Is the stock of a plasticy nature? , if so, you will hear like a crack noise on impression.... it will also deteriorate your die-forme quicker if you are running large quantities.. make sure your packing/ cutter height is correct
     
  9. alibryan

    alibryan Senior Member

    Joined:
    May 2014
    Messages:
    150
    Location:
    Pacific NW
    I’ve always wondered about the reasoning in putting any kind of buildup behind certain areas of the die. I know it (sort of) works, but when you stop and think about what you’re actually trying to accomplish with that, it seems a little odd to me. I used to find that putting make-ready behind whatever it is that you’re trying to cut (i.e, the stock), seems to work better. Similar to if you were using the windmill for printing (no jacket), where you would build up behind the Tympan paper.
     
    Last edited: May 24, 2020
    printerdan likes this.

  10. narayan

    narayan Member

    Joined:
    Dec 2009
    Messages:
    49
    Location:
    Nepal
    Which size is your machine? There are 2 sizes 10x15 and 13x18 and both have different saftey mechanism. 10x15 has saftey collar at back side below oil tank. 13x18 has saftey pin at right side of body.
    You can search for operator manual in internet.
     
Loading...