Converting a small offset press to letterpress

Sounds like an interesting project. Although it should be a matter of proper selection of photopolymer plate thickness and type of plate. This due to the limitation of adjustment of form rollers, for proper inking and also the limitation of plate cylinder adjustment for gap to blanket.

Be aware that because of the difference in height of the plate from the plate cylinder, you will be dealing with linear stretch of the image. Usually requiring compensation in image making, how ever you are applying the image to the plate.

In years gone by squeeze lenses for process cameras were sometimes used to accomplish that. Good luck!

PS: Halm super jet presses used to be available to accomodate some letterpress stuff, you might find one still around. The offset version of that baby could print 60,000 #10 envelopes an hour, quite a machine if setup properly.

It seems to me that the old Davidson 221 model had a removeable sheet or segment whgich could be removed to use relief plates. Does anyone have experience with these? I ran one, but only in litho mode. I would think the impression would still be offset onto the blanket for the printing.

Heidelberg made a series of presses (including the KORD) which had the capability of running thin relief plates instead of the litho plates. I actually did run one of these using relief plates when demonstrating the capability for students in one of my classes. We did 4-color work from photopolymer plates. This also used the offset blanket to transfer the image. The only advantage was elimination of the dampening solution and the ability to print fine halftone images on firly rough stock. Heidelberg called this “Letterset” to differentiate it from Offset.

John Henry

Updated. Yes you can. Remove the water unit. The cylinder for the offset plate just inks up totally. The rubber plate or photopolymer plate is attached to the cylinder instead of an offset blanket. We used to do this all the time to imprint hosiery packages. They were called L-Boards, I-Boards or V- Boards. You do have to adjust the cylinder pressures.
Done it on a Davidson, Mult & AB Dick.
Bob

Re the KORD, the KORD in my firm was actually delivered new with a letterset shell, as a sort of spare, but in common with union shops in London at that time - it could not be used, not by a litho union card holding machine minder. It gathered dust in a corner and was never used.

Any visitor to the Heidelberg factory or to print exhibitions at that time saw it demonstrated.

Yes, the Davidson was my first press. It would print bothsides of the sheet in one pass. The plate cylinder was twice the blanket cylinder - the first half of the plate would “offset” to the blanket - the second half would print directly on the face of the printed sheet from the reversed image on the second half. The press had no back cylinder in essence other than the blanket cylinder acting as one. About 1975 story and the press was ancient then. Had 3 kids in Dr. Dentons and were poorer than church mice. Set the shop up under the car port outside. I don’t miss that much I will tell you. I did try printing a 300 line screen halftone on it once and it did pretty well. Georgia O’Keefes’ portrait I think.

I ran one of those Davidson presses, a perfector, in the early 70s that was old then, as Calvinc mentions. It was convertible for letterpress printing with some sort of flexible relief plate. We never used it for letterpress though.

Aside from that machine I think it would be pretty difficult if not impossible to convert an offset press such as a Multi or A.B. Dick as the plate cylinder to blanket cylinder impression probably couldn’t be backed off enough to prevent the plate from hitting it too hard. You’d also have a problem backing off the form roller to plate pressure. Even if you could somehow work that out, what do you have? Offset printing. Why not just eliminate all the fooling around and use offset plates? The results would surely look better.

A better choice would be to get a Miehle verticle letterpress. You’d have an automatic feed press that’s cheap and usable with polymer, type, or linotype. It’s also a very popular press with trade shops that do die cutting, scoring, numbering, etc. as it is fast to set up and easy to run.

There is a very busy offset shop in Madison WI that has converted a couple of Multiliths to use with photo-polymer and printing carbonless business forms with very good results. I don’t know how they did it but it sounds like a “modern” letterpress to me!

Updated. Please refer to my above post, I have done it many times years ago. Instead of a offset printing blanket (which you remove) stick on the polymer plate & it will work. Pressures must be adjusted. The offset cylinder (that’s where the offset plate would normally go) inks up totally. You can run it as fast as you want to go. 5,000 to ? per hour.
Bob

Updated. I’ll concur with what Bob says. Our shop used to do it on AB dicks all the time. They would use a “rubber” plate, most likely a photopolymer, that was the same thickness as the blanket. Most the time they were just sections win an adhesive back. Leave the water out of the fountain, ink an old metal plate up completely and away you go. They mostly did it for envelopes, but some “box” work that they didn’t want to smash up a blanket on.

I am reading this thread with great interest since I have access to a small offset press. I have one important question however before I would ever try this. What is the advantage… reason… to convert an offset press to letterpress? Wouldn’t I still have an offset press?

I would still be an offset press. You can put the rubber blanket back on, hand a plate add fountain solution, reset your pressures and all would be well.

I can see an advantage in printing envelopes as my shop did since this method eliminates water issues very common with running envelopes.

I can also see how this would be the only way to crash print NCR forms if you don’t have a true letterpress for the job.

Aside from that, it’d just be for the fun of doing it ;)

I still have my Davidson 221 and it still runs great. I do remember running it with the Gent that sold it to me both sides on a single pass. The off side of the sheet was not as sharp as the offset side. It might have been because the film used to make the plate was not RRED, or how would you say it, wrong reading emulsion down I guess, we should have went around with it. The type had to be a mirror image on that segment. Also still have my 26” hand cutter. I run the press from time to time just to keep it from rusting. LOL

I am hearing about a process of using offset plates that read backward and printing right against the paper. Is that what is called “dry offset”?

What you describe is not offset (which uses an intermediate blanket cylinder) but would be direct lithography. Dry offset puts a right-reading shallow relief plate on the plate cylinder and doesn’t use dampening, and is what Heidelberg called letterset (though I think it was first developed by Miehle). There is also waterless lithography which relies on special plates, inks, temperature control to achieve image separation; that is a high-tech and expensive process.

Back in the 80’s a UK Publisher advertised for an invisible ink printer for childrens books, with help from an ink maker we printed many thousands of the books using aluminum backed polymer plates printed on a B1 (1020 x 720) Heidelberg SORS. The plate was mounted on the plate cylinder with some of the packing removed, of course the image had to be right reading.