Last week I was looking at a plain (no frisket) power Universal I AB which was running erratically; turns out the driving gear had loosened and was binding against the housing that covers it. Then we tried to readjust the clutch according to the manual. But when there is just enough clutch friction to pass the trip cam, it isn’t enough to get over the cylinder check cam from the feed board position. Next we’ll disassemble the clutch and clean it and see if that improves the situation.
Then, trying to follow the limit switch cam adjustment instructions, the cylinder stops at 1″, rather than the specified 1 -5/16″, and that difference happens to be the same as the thickness of a bumper leather. There are the mounting holes for bumper leathers behind the cylinder, but they are only present at the front.
So, can anyone tell me if bumper leathers should be present behind the cylinder on this press? Or are they not used in direct contact with the bumper springs?
Alex and Daniel, thanks for the comments. This particular press differs from both of yours in that without bumpers, the cylinder does go closer to the feed table than is recommended: I had hoped that was the problem, but no, more fine adjustment is needed. (For comparison, I looked at another power Universal III AB/frisket, but it had no bumper leathers at all, not even the threaded mounting holes.)
The thing is, I was adjusting those cams that contact the limit switches, and there was no latitude for adjustment. The cylinder either stopped too far away or too close, couldn’t find an in-between point. Cylinder check cam spring seems fine to me, unless power models uses weaker springs than manual models, where a weak spring lets the cylinder creep forward.
I do think I am going to need some Loctite before to finish this. The screw that holds the driving gear (this is on the cylinder drive, not the roller) has nothing to retain it in place. Now that is is loose, it can easily work outward again.
My only power Universals are IIIs, but I expect they are quite similar. On the back of the press have you adjusted the part mounted to the cylinder carriage that triggers the limit switches on the back of the press? You can adjust it left and right, but also spread the ends apart.
I don’t expect you’d want a bumper leather between the carriage and the spring at the feed board end. On my hand cranked Uni I AB if they were present they’d prevent the carriage from coming back far enough for the sheet approach to the gripper bar to be managed easily.
As for the issue you mention with the clutch, is the cylinder check cam spring correct? My rule of thumb when adjusting the clutch is adjust it just so tight that the press will function correctly. That way it will give if the press hits an obstruction like a forgotten quoin key, but not slip on a heavy form.
The Arm Letterpress
I have a Uni I hand powered, and i’ve had the same issue with the screw loosening on the far side of the roller. It happened before I had the press too, because the paint is worn away there. Now I check it every once in a while to make sure it’s snug.
My carriage only has leather bumpers on the front, even though there are holes on the back. I put a bumper inbetween the carriage and the spring and it doesn’t allow the cylinder stop to engage – so i don’t think it was ever meant to be there. The paint is also worn away where the spring contact, so that’s more proof. Don’t know how different the powered model is, but there’s my two cents.