roller pressure
The need-to-know-basis information is available:
Take a Heidelberg with original rollers, order some ink formulated for the press, run-up the ink, set the ink strip from 10 to 12 points. There is a pile of set-up sheets beside the press, stabilise the ink flow, lock-up the lead type and print a million pages for the Bible with kiss impression. If you make a deep impression and smash the type, you are out of the job.
Well, a lot has changed since then. The Heidi is not new any more, the rollers are after market and the ink, most of us use, was formulated for duplicators with fountain solution. Set-up can be done only on the same stock as the job is on, and it cost about $1 a card ( Lettra #220 in Canada ), so set-up sheets are not abundant. We are not kissing the impression any more, it has to be deep and the plates are photo-polymer.
So, setting up roller pressure on all the rollers on the press is important.
Can anyone explain in layman’s terms, what’s happening when the roller pressure is high or low?
Not just on the printing plates, but on the roller to roller contact too.
Louie
http://eagleprint.ca
OK, since you have had no response to your query, I’ll give it a try.
First of all, on most presses the operator’s main task is the setting of roller height, not pressure. On the Heidelberg platen, the roller height may be set as on other presses, with a roller setting gauge held in various areas of the bed, using the adjusters at the outside of the bed to raise or lower the rails to get the height required. I would have to say that a 12pt.-wide stripe might be a bit too much for most applications. If the rollers are set too close to the printing surface, they will push the ink off the surface and force it over the edge, leaving inadequate ink on the surface for good printing. The drum on the press is set to contact the rollers properly if they are set properly into the saddles.
One idea I would share with you to save $$$ in set-up stock is to find you “sweet spot” for impression on the expensive stock, then run in some other less expensive card stock to see what thickness of stock gives you a good image (note I said “image”, not “impression”). Then you can do the initial image setup for future jobs on the less expensive stock, and the thicker, cushier Lettra will provide the proper depth of impression, and the final appearance you seek. You most certainly will find that the Lettra will drink in more of your ink, and you will have to add ink before you switch to the Lettra, but experience with the card stock images will help you determine the effect once you switch to the “high-test” job stock.
If I haven’t totally answered your query, lets continue the discussion on-line as we can all benefit from learning what others do.
John Henry
Cedar Creek Press
Hello John, and thank you for your response.
I am happy to hear that you are open to on-line discussion to benefit others too.
I think I should have skipped the first two little bit exaggerated paragraphs in my post. My real question is on the bottom. I used the expression “pressure”, because I was referring to the force with which two rollers mate. Theoretically the printing plate can be looked at as an infinitely large diameter roller too. And on some presses, they are bent around the roller.
I am planning to make some changes to my Heidi, but perhaps later about that. What I would like to understand is, what is happening in the roller train with the ink.
Some people take things granted, some question everything. I am the latter one.
For example;
a while back I purchased a set of four rollers from SYN-TAC. To my surprise the form rollers were softer than the rider and ductor rollers. They all work fine.
I think that from the manufacturing and inventory stand point it is costlier to produce rollers in two different hardness’s.
so, WHY is the hardness difference?
Louie
http://eagleprint.ca
Louie:
I really do not know why the manufacturer would ship differing durometer rollers for doctor/distributor rollers vs. form rollers. Personally, I use my newest and best rollers on the form rollers on my cylinder press as the contact with the plate is most critical ink transfer point in the system. When they begin to age, I move them to the distributor roller position and purchase new form rollers. On my cylinder press all the rollers are interchangeable except the doctor from the ink fountain.
On my platen press, I put my best rollers in the lowest positions in the saddles as they are the last to pass the form prior to impression.
If you are using various materials in your form (type, rule, illustrations of various types, the lower durometer rollers will be most likely to conform to slight differences in height in the form (some slight height differences are inevitable).
In ducting ink from steel rollers, you have a very uniform contact line, so a harder roller might do a good job and wear better.
I have to admit that I’m just giving you my best guess on this. Your best source for information is SYN-TAC or your preferred supplier. I did find a spec sheet on SYN-TAC’s H Platen rollers, and it just indicates that all the rollers supplied are “soft rubber.” See link below:
http://www.therollerstore.com/rollers/syntac_rollers/syntac-catalog-23/0...
John Henry
The Syn-Tac sheet for the Heidelberg T 10x15 also shows the same part number for all the rollers in the kit. If they are the same part number, the hardness shouldn’t vary.
To Louie: the rider roller (there is only 1) on your Heidelberg T is metal and of much smaller diameter than the rubber rollers.
Michael
When I had rollers made for a Heidelberg cylinder, they were intentionally made in three durometers. Hardest was the ductor, distributors were medium, and softest were the form rollers. Letterpress form rollers should be softer than offset form rollers, but the fountain and distribution functions are pretty much the same in letterpress and offset ink systems.
Photopolymer work benefits from harder form rollers than typemetal and photoengraving work, and also demands very precise roller setting. A 12-point stripe on the roller gauge is far too low. Try a nickel’s thickness.
I stand corrected ! all four SYN-TAC rollers are the same hardness.
At the time when I got them, I tested them with my fingers, and the ones without the the bearings appeared harder. Since then I bought a Shore A durometer, but never used it till tonight. I went to my shop and checked all the different rollers I have laying around. All of them are used, and many of them are damaged ( not by me ) from the numbering machines and perforating rulers.
here are the results for reference:
- composition roller…….15 falling to 10
- two rubber roller………40 falling to 32
- green rubber roller……35
- SYN-TAC roller………..40
- red rubber roller……….42
- Chinese roller…………..anywhere from 48 to 58 ( LOL )
These are not laboratory test results. I found it interesting how the first two listed rollers hardness’s were falling as time went by. The rest of the rollers kept the indenter pretty much in the same place.
I don’t know what is the proper name for the second roller listed. It has two layers of rubber, the inner thicker layer is a very soft rubber ( dark brown ) and it is capped off with a thin layer of harder rubber ( black ). I managed to salvage a piece of it, and slipped it over a 3/4” hand roller. Now I am using it to edge paint.
The composition rollers are very soft and tacky. I guess, as they age, they become softer and softer before they turn in to goo.
I find parallel_imp’s note very interesting about the rollers intentionally made in three durometers.
I will be back with my questions.
Louie
http://eagleprint.ca
I would judge your SYN-TAC rollers to be pretty hard for letterpress printing. The proof will be in the printing.
I too have a set of rollers that has a sleeve pulled over a soft spongey inner core. They came with the press and I had not seen rollers like that before. They print well.
side-line questions:
- anyone measures the hardness of their rollers?
- anyone tried to soak their rollers in a 3% lye solution as suggested by the Heidelberg manual?
Louie
http://eagleprint.ca
Yes, I do check the durometer of my rollers. I like between 25 and 35 for use with mixed forms of type and cuts, but a bit harder roller should be fine with printing from plates only.
I have used “Easy-Off” oven cleaner to clean rollers on which ink has dried and has filled the pores. It works well on rubber rollers, but must be removed very quickly on composition rollers as it will rapidly dissolve the roller. It would be a last resort for composition rollers. This cleaner has a component of caustic like the lye, and works wonders if used for deglazing or deep cleaning. Do it carefully, with rubber gloves and eye protection.
I guess, that you have several sets of rollers, and you choose the hardness suitable for the form.
What bugs me is, that I did not have a durometer when my rollers were new, so I don’t know how much hardness I added to them over a year and a half of use.
I occasionally use Zep - Industrial Purple to clean my rollers off-press ( it would damage the chrome-plated rollers ). I guess that the lye / oil chemical reaction creates soap, which can be washed off with water. I wonder how would it affect the roller durometer, soaking them in Zep solution over the week-end.
What makes the trumpet shape at the end of the rollers?
Louie
http://eagleprint.ca
The flare or increased diameter at the end of the rollers is due to incorrect and incomplete cleaning. The ends of the rollers must be thoroughly cleaned with a good hard scrub.
The ink migrates to the ends of the rollers and is absorbed and hardens. It causes the roller to flare.
I clean my rollers off the press. When finished, I use a dry paper towel and give a good hard scrub to see if there is any hint of ink left. If so, more solvent and harder cleaning.
time flies when you have fun, eh? I neglected this post. in a meantime I did made a durometer stand / roller soaker. and checked again my SYN-TAC rollers: 37 Shore-A after 15 seconds, at 23 deg. Celsius with 1Kg load.
any other suggested method to obtain a lower reading? … LOL
the contraption is made out of plywood. I will need to coat the inside with epoxy or polyester. which one is better resistant to 3% lye? and how to mix the 3% lye?
this is just a trough to soak and slowly rotate the rubber rollers in 3% lye solution to remove embedded ink. a week-end beauty treatment for the rollers. without the lye solution in it, it also serves as a durometer stand.
Louie
http://eagleprint.ca
soakerdetail.JPG
rollersoaker.JPG
durometerstand.JPG
There is a difference between roller Durometer and the original topic of roller pressure. I was somewhat amazed at Louie’s methodology for measuring Durometer. I located in the Vandercook files their method for measuring Durometer and it is the method we use as well as the roller makers we use:
https://www.flickr.com/photos/53177163@N00/25866287320/in/dateposted-pub...
hello Fritz1,
I will get back to my original topic. this was just a side excursion in to roller durometer reading. thank you for the link, I downloaded and saved it. first time that I did see any reference on how to measure the actual roller’s hardness. I think that the Vandercook method allows for a wider range of readings than my method. the thing is what I don’t understand is that my readings are way off. could it be my cheap Chinese durometer?
don’t misunderstand me, I have no problem with the rollers, they work fine, my prints are very crisp and even. I was just curious about the roller hardness, and I am now more puzzled than before … hahahaha !
anyway the original topic has to do with the picture I posted in the Heidelberg Ink Well topic. setting the pressure/force in-between the various rollers, and I have two extra rollers there!
Louie
http://eagleprint.ca
Louie—read carefully the Vandercook explanation on how to take a Durometer reading. It is read in the first second, no added weight as you have devised, and not over a length of time. It is your technique, not the instrument from China.
As for roller pressure, I came across a drawing from the Miehle company that Vandercook was using to adapt their ink monitor to the new V-50X Vertical press. This was requested by Deluxe Check Printers who were buying these presses in quantity back in 1965 and later. Deluxe wanted to accurately measure the thickness of the film of magnetic ink they were applying to the checks they were imprinting. They show the 2 form rollers being set to the ink plate using a .004” feeler gauge. We have all learned to set vertical rollers by the width of an ink stripe to the ink plate. See:
https://www.flickr.com/photos/53177163@N00/26079729631/in/dateposted-pub...