I recently had the form rollers on my SP-20 recovered and I’m having trouble getting a decent print out of them. The short version is that my printing is slurred. The detailed version is that, if printing a line of type that’s parallel to the gripper bar, the rollers will print heavy towards the top and bottom of the line and leave the center fairly ink-starved. The ends of the line might also be slurred with the letterforms looking as if they’ve being dragged slightly downwards. I figured that the fix would be in adjusting the roller height but that doesn’t seem to work. I’ve checked my packing as well. I’m starting to suspect that the problem may be in the finish of the rollers. The service that recovered them talked me out of a high gloss finish and instead advised me towards a “matte” finish.
My questions are: Can roller finish cause this sort of slurring, and, what are the best specs for recovering form rollers on an SP-20 (especially those to do with finish)?
Thanks for your reply, Eric.
Yes, I’m using photopolymer and it’s true that the old rollers were shrunken. I’ve got my hands on a feeler gauge set and will attempt to adjust the carriage bearings and then the roller settings. I’ll report back on my progress!
You don’t mention the nature of the form. Photopolymer? Such a form can handle much harder durometers, but requires light and very precise roller settings. With the slight variations inherant in a metal form, softer rollers, set lower, were the standard. But with photopolymer you really need to know exactly where your surface lies and set your rollers to actually roll over the surface, without slurring or pressing beneath.
I am running 25-year old, 45 durometer form rollers on an autocylinder and still getting crisp inking (but with a metal form I have to add a newer, softer form roller in the No. 1 position to get coverage on the low characters). I doubt 26/28 durometer rollers are the problem.
If the change in print quality happened with roller change, I would think that roller setting is the thing to refine. Your previous rollers probably were not the exact same diameter as your new rollers. New rollers may be oversize, old rollers are most likely shrunken.
Hmm, checking again it seems that the durometer is 26/28. Assuming the extreme, would 28 be too hard to work with? I’m suspicious of the rollers because this particular slurring problem is new since I received the recast rollers.
Good to have some data to work with. A26 isn’t all that bad. Our friend Gerald Lange declares, in his that A25 is better for printing polymer and I defer to him.
A gap between the under rail and a carriage bearing the width of a popsicle stick—even a Canadian one : ) —is much more than Vandercook intended. Read Gerald’s article on this site at https://vandercookpress.info/vanderblog/literature/articles/lange-adj/, then use 003″ automotive feeler gauges placed between the carriage bearings and the under rail as a starting point. it will likely require some trial and error to accommodate the particular wear history of your press.
Hopefully, other SP20 operators will chime in soon, but please keep us apprised of your progress.
Thanks for your reply, Paul.
The specs are indeed 3″ in diameter but the durometer I was advised to use by a local press expert and dealer was A26 or so.
The woodruff key and set screw are in place and the gear is aligned with the rack.
I’ve noticed (and I’m embarrassed that I didn’t notice this before) that the carriage bearings under the rail are out of whack. The rear one on the operator side has enough clearance between it and the rail to lodge a popsicle stick in there! Fritz mentioned (in his recent reply to Clawhammer Press’ inking concerns) that these bearings control racking and cylinder alignment. Maybe their current condition can be used to explain both the gouges in the rails and the now occasional chattering rollers that I previously posted about. Trouble is, I’m not confident that I know how to adjust the bearings. I certainly don’t have the “prior mechanical experience” that Letterpress Commons suggests I should before undertaking the adjustment.
Finally, the press bed is .968″ with a bed plate and the form is type high.
Matte finish is what you want. But let’s confirm all the specs:
The roller diameter for the SP20 should be 3″ and the durometer (hardness) should be A20.
There should be a Woodruff key (small half moon disc) aligning the gear with the core.
A set screw locks the position laterally on the core and aligned with the form roller rack.
I checked your previous two posts neither which mention if the bed is .918″ or 968″ with a bed plate.
Is you form type high?