Or as happened recently on my SP25, what if the whole mechanism locked up, and you couldn’t even advance the cylinder beyond the feed board.
When that happens, it's time to consult the manual and study the intricacies of the print/trip mechanism and the “trip spring” which actuates the whole thing.
Shown are four pictures I took while I and a fellow printer removed the side plate from the cylinder in order to get at the broken trip spring.
The first picture shows the undercarriage, with the print lever lodged behind the trip roller. As I could not advance the carriage from the feed table I was unable to get at the trip spring.
Otherwise I could have got at the broken spring, when I ran the cylinder to the end of the press bed.
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Once we got the side plate off, the broken spring was quite apparent. On close examination of the break, it appeared as if the spring had broken a long time ago, as the break was dirty, and the broken half was nowhere to be found.
(The press is operational with only one spring.)
As to how the print lever got hung up behind the trip roller: I think that may have happened when I “short-stroked” the cylinder. That is, I advanced it in Print, then changed my mind and brought it back, without having gone far enough to go into Trip.
As a rule I always complete a print cycle, even if I know the sheet is misregistered; as once you get into the middle of the press and try to return the cylinder, the sheet can hang up and catch in the rollers, creating a very inky mess.
I received considerable advice from friends and colleagues, most notably, Paul Moxon, who sent me a list of the steps in removing the side plate.
So you are looking at removing:
- tie rods holding the two side plates together
- oscillator assembly
- roller support, if present
- trip bearings
(Note in the upper-right-hand corner of the second photograph, what may be called a synchronistic curiosity or prestidigitation: the tiny No. 01 Ball Bearing Vandercook Proof Press, seemingly tucked under the feed table of the SP25.)