Flickr letterpress

I was going through a photo stream when I found what appears to be a Heidelberg press. I am not certain.

http://www.flickr.com/photos/eholubow/2193815027/

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Looks like one of their early offset presses to me, but it could be a large cylinder letterpress. Certainly Heidelberg

It is a K-series offset press. If the plaque was readable, you’d see offset/letterset.

I’ve always wondered about the letterset moniker. I may be remembering incorrectly, but the rotaspeed line they produced were also labeled as letterset, were they not? Does letterset refer to printing flexible relief plates from a cylinder? That’s certainly what the rotaspeed presses did. If so, are K-series presses also capable of doing this? This isn’t the same thing as dry-offset, is it?

Letterset is just using a wraparound relief plate on the plate cylinder of an offset litho press (and originated by Miehle, not Heidelberg); it is not the same as rotary letterpress, which is direct not offset. You could call it dry offset, but then there are other ways of waterless lithography now too.

If you’ll continue to allow me to pick your brain, I’ve got more questions:

As far as the letterset process is concerned, how do these presses compensate for the difference in caliper of an offset plate and a relief plate? Do they simply have a large amount of adjustment available to the pressure between plate and blanket cylinders?

Second: How does the letterset process differ from flexography? My understanding of flexo was that it was just that, wraparound relief plates printed offset.

Thanks for the insight.

Paul

Flexo prints direct from the plate; with letterset/dry offset the image is inked on the right-reading plate and offset to the blanket, then to the paper. Deep impression is not possible with letterset ;-).

Bob

Wraparound plates on offset plate cylinders weren’t used until very thin relief plates were developed, such as photopolymer and Kodak Relief plates; it couldn’t be done with traditional photoengravings or duplicate plates. Photopolymer can be .017 total thickness, which will fit on larger offset press cylinder undercuts. There is no adjustment between cylinders (they run bearer-to-bearer), just varying packing to fit plate to cylinder undercut. For example my Chief 22 has a .016” cylinder undercut, and a .017” photopolymer plate would fit at a perfect .001” over bearer, where a .010” offset plate would use .007” packing for the ideal height. I don’t know what the undercut on Heidelberg KORD is, but I think they may have used different shells for offset plates and wraparound plates.
Flexo is an entirely diffferent process using different presses, plates, and inking systems.

Strange, I run a duplicator (a Gestetner 202) and it has cylinder pressure adjustment. I am assuming that is because it was designed for simpler work and shorter runs, so pressmen are not going to be inclined to pack the blanket cylinder or create underlays. I’m not sure exactly what the range is, but if I remember correctly from the instructions it’s designed this way to accommodate different blanket thicknesses as well as help compensate for blanket wear. A similar pressure adjustment is ready for blanket to impression to compensate for paper caliper.

Thanks for all the info everyone.