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12879Re: [PPLetterpress] Laser Engraved Photopolymer Plates

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  • Gerald Lange
    Oct 23, 2011
      Hi again

      Metal foundry type does have a sloped relief and the photopolymer plate
      process somewhat mimics this.
      Laser cutting would require sophisticated relief modeling software to
      achieve this with letterforms. I suspect many national mints are
      employing such in the production of coinage, but hand modeling far
      outshines this process. Contemporary Latvian coins are a superb example.



      On 10/23/11 11:52 AM, Scott Rubel wrote:
      > Well, it was worth a thousand words to someone asking about the
      > structure of a plate exposed with a negative.
      > I was just relating my own limited experience with lasers and assumed
      > this would produce straight sides which, like metal type, are more
      > forgiving with imperfect rollers and adjustments, thus one less thing
      > I have to teach an employee.
      > Always looking for the easy way.
      > --Scott
      > On Oct 23, 2011, at 11:28 AM, Gerald Lange wrote:
      >> Scott
      >> Hmmm, I guess a picture isn't worth a thousand words.
      >> No, these are not laser cut, these are film exposed. Obviously,
      >> there would be a difference in the relief structure between the two
      >> processes. That was the point. Film based photopolymer has varied
      >> relief, that is why it works, and, ahem, why this should be a
      >> consideration in presswork.
      >> Gerald
      >> http://BielerPress.blogspot.com
      >> --- InPPLetterpress@yahoogroups.com, Scott Rubel<scott@...> wrote:
      >>> These are very clear pictures, but are these laser cut? Is there no
      >>> difference between the structure of plate exposed to a negative and
      >>> one from a laser?
      >>> --Scott
      >>> On Oct 23, 2011, at 10:21 AM, Gerald Lange wrote:
      >>>> Scott
      >>>> Maybe a picture or two is worth a thousand words:
      >>>> http://www.flickr.com/photos/bielerpress/6272724517/in/photostream/
      >>>> #/
      >>>> photos/bielerpress/6272724517/in/photostream/lightbox/
      >>>> http://www.flickr.com/photos/bielerpress/6273250924/in/photostream/
      >>>> #/
      >>>> photos/bielerpress/6273250924/in/photostream/lightbox/
      >>>> These are microscopic views of the surface of a halftone image. This
      >>>> is
      >>>> why photopolymer can provide such exquisite detail. The relief depth
      >>>> between imaging of close proximity decreases with exposure and
      >>>> provides
      >>>> structure.
      >>>> Gerald
      >>>> http://BielerPress.blogspot.com
      >>>> On 10/23/11 10:00 AM, Scott Rubel wrote:
      >>>>> Gerald,
      >>>>> Good thinking about all this. I certainly would want it to be a
      >>>>> minimum of 2400, for one thing, but I have not known how to think
      >>>>> about the other disadvantages.
      >>>>> The thing that I hope for when I think about the potential of laser
      >>>>> is
      >>>>> straight sides to the raised type. I don't I understand why there
      >>>>> would be a limit to the depth in a counter as opposed to any other
      >>>>> part. My knowledge of lasers is based on mostly half- or 3/4-witted
      >>>>> speculation mixed with fantasy, which is why I do not understand
      >>>>> your
      >>>>> last paragraph, but I trust your assessment.
      >>>>> --Scott
      >>>>> On Oct 22, 2011, at 10:57 PM, Gerald Lange wrote:
      >>>>>> Scott
      >>>>>> I suspect that if cut just short of the floor of the plate rather
      >>>>>> than down to the backing there would be no problem with the steel
      >>>>>> reflecting. A more significant concern would be cutting through
      >>>>>> the
      >>>>>> pre-exposed floor as plate stability would be sacrificed.
      >>>>>> Actually,
      >>>>>> with this technique, the thinner the plate the better. All that
      >>>>>> I assume the identity of the plates themselves and the correct
      >>>>>> timing for the exposure is a minor problem. 1200 dpi is still not
      >>>>>> good enough, basically high-end laser printer quality. Imagesetter
      >>>>>> quality at a minimum of 2400 dpi would be needed to match current
      >>>>>> film based exposure.
      >>>>>> A major concern would be maintaining relative reverse relief
      >>>>>> depth,
      >>>>>> which is fairly uniform when exposing photopolymer plates
      >>>>>> specified
      >>>>>> for letterpress applications, no matter what the thickness of
      >>>>>> plate.
      >>>>>> For instance, the relief depth of the counter of a small point
      >>>>>> size
      >>>>>> lowercase e or o is not going to be open to the depth of the floor
      >>>>>> of the plate. It is halted with maximum exposure at a specific
      >>>>>> range, about .30 mm; relief depth is not uniform [which is
      >>>>>> actually
      >>>>>> the best technical argument refuting the practice of extreme
      >>>>>> impression]. I don't see how this could be controlled with a laser
      >>>>>> cutter.
      >>>>>> Gerald
      >>>>>> http://BielerPress.blogspot.com
      >>>>>> --- InPPLetterpress@yahoogroups.com, Scott Rubel<scott@> wrote:
      >>>>>>> The website days it goes to 1200 dpi. If the coordinate
      >>>>>>> tracking is
      >>>>>>> accurate as it cuts, that should render pretty good six point
      >>>>>>> type.
      >>>>>>> It is hard to tell the quality of the laser, but I think I will
      >>>>>>> ask
      >>>>>>> them for a sample of steel backed polymer. I wonder how that
      >>>>>>> works
      >>>>>>> without the steel acting like a mirror.
      >>>>>>> These laser beams can be unbelievable thin, if they are high
      >>>>>>> quality.
      >>>>>>> I work at a place where we make giant cameras for giant
      >>>>>>> telescopes,
      >>>>>>> and we order custom "slit masks" which are large sheets of
      >>>>>>> aluminum
      >>>>>>> with thousands of precision placed cuts in them. The cuts aren't
      >>>>>>> much
      >>>>>>> thicker than a hair, and you would think the laser is just moving
      >>>>>>> along a path and cutting the slit, but in reality it cuts out the
      >>>>>>> shape of the slit and almost microscopic blanks fall out of the
      >>>>>>> metal
      >>>>>>> every time a slit is cut. So if this Epilog Legend 36EXT
      >>>>>>> machine is
      >>>>>>> high quality, I would think six point type should work fine.
      >>>>>>> --Scott
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