I just started working with a friend’s No. 4 press. It prints great and seems like a really solid machine. The machinery used to lower the impression cylinder from trip to print during the print stroke then back up to trip for the return to the feed table seems very different compared to the SP series trip assembly. I was curious about how it all worked and consulted Paul’s book. I found the No. 3 & 4 trip assembly illustration on page 12 (attached for reference). From Paul’s narrative in the book and having watched the trip roller/cam follower travel during the print stroke, I see how the trip roller (BR-134) rolls onto the top horizontal support channel/safety bar to raise the cylinder trip rack (M-183) and cause the trip gear (MR-43) to rotate forward/counter-clockwise (viewing press from non-operator side).
What I don’t get is: how is the trip gear “pinned” to the cylinder eccentric in a way that lowers the impression cylinder into print mode? All I can see is the trip gear rotating counter-clockwise to move the press into print mode but how does its rotary motion trigger movement in the cylinder eccentric? Am I missing something really simple here?
Regardless, I loved printing on this press. The clacking sound of the trip wedges at the beginning and end of the print stroke were so soothing, almost therapeutic! Thanks!