Sunday, September 13, 2015

Ink coverage problem

Roller hook and armature causing coverage problem

I was having a problem, which seemed to be getting worse over time, with an area in the middle of the image on the left side of the Pearl #3 press.  Ink coverage was light in about a 2 inch band running from the middle of the left edge inward about 4 inches. Flipping rollers and even swapping them didn't seem to help.  I thought it perhaps was the springs. There was also an odd ink density variation (about the same size) on the ink disk that seemed to be related. 

Purchasing a roller gauge I could see that the problem existed with the rollers, not with the bed or platen of the press.  This led me to look more carefully at the trucks and the hooks. With newly taped rails I noticed that the upper left truck was rather sloppy forward and back within the hook while the bottom was only sloppy a bit up and down. On further inspection it looked as though the inside of the hook had worn enough that the roller was not pushing the hook end away from the hook armature — that the end of the hook was pressing against the hook armature so that the roller was sloppy. (Because the bottom hook does not hit the hook armature that roller seated well enough and the up and down sloppiness doesn't seem to matter.)  I did not want to tape the truck as the friction inside the hook would be a problem and the trucks are locked to the roller. By filing down the end of the hook so that it did not hit the hook arm the roller now seats properly in the hook. The opposite side did not show this problem but I filed it down a bit too to prevent future issues.

So that was it and the problem has disappeared. Yippee!!