Plate movement
I’m having a lot of trouble today with plate movement on my SP-20. It’s a fairly large steel-backed plate (I’m printing 4-up 5x7 postcards). I was originally using a large patmag. The first run I did last week was fine; no movement. Today, the plate is sliding all over the place. I tried duct tape, that didn’t do anything. I tried switching out my base to a couple smaller buntings. The plate hangs over the edge of the base, which is one problem, but it’s also still moving slightly.
Is this typical of steel-backed plates on the Vandercook? Could it be b/c it’s such a large plate? I imagine the overhang on the smaller buntings could be an issue if the lip catches on the roller. Can carriage speed (i.e. faster rolling vs. slower) affect this?
I’m thinking of cutting the plate in half to do 2-up and seeing if that will help settle things down. My other thought is to give up on the steel-backed and get a new adhesive-backed one.
I would think this kind of plate creep would be a problem with a cylinder press. How much impression pressure are you running. Is it moving a lot with each impression or a very small amount each time? Could you mount the plate so one edge is flush with the edge of the patmag and then lock up something just a tiny bit higher than the patmag along that edge as a stop against which the plate could not move?
Bob
Jonsel
You should expect plate travel with a PatMag, it has a very weak magnetism. But a Bunting, no. Is there perhaps oil or solvent on the bases? or on the back of the plate? Is your lockup proper? Did you redo packing during the run? There are other possibilities. Maybe go through the procedure again, any changes made could cause registration problems.
I’m not sure what the arrangement of the smaller Bunting bases would be that could cause a problem in this regard but sever impression might. Also, Vandercooks should never be fast rolling. They are proof presses.
Only thing I can add here is that I have used PatMags, Buntings, Boxcars, and the Eluminum. Never had this problem with the Bunting bases, unless through operator error :—)
Gerald
http://BielerPress.blogspot.com
Jonsel
Secondary thought.
Are you using a lockup bar?
Gerald
http://BielerPress.blogspot.com
Gerald,
I think the problem I’m having on the buntings is b/c the plate hangs over all 4 edges. My patmag is 13x19, and the plate fits safely on the base, but I only have two 6x9 buntings. I wouldn’t be surprised if those loose edges are getting bumped by the rollers. On the patmag, the plate was sliding toward the feedboard. On the bunting, it was sliding away (not nearly as much, I should say).
I am using a positive lockup bar, but there was no movement in the form itself.
And yes, I’m fully willing to embrace it as operator error… I’m just hoping to find what my error was. Someone else suggested impression as well. The paper is Mohawk Superfine, which is a lot harder than Lettra, etc., so even though I’m not hitting it hard enough to cause impression show-through on the reverse, maybe I’m still hitting it too hard.
If you have a hard packing, there is no-show on the back as the pressure just completely compresses the paper. Don’t count the sheets for your packing, measure it, Any cheap digital caliber will do fine.
The correct packing, Roller height and it should eliminate a lot of your trouble.
If you are haing forward creep, and the plate is trimmed exactly square at the head, you can take a piece of brass rule or scoring rule. and grind it down to where it has just enough lip above the PatMag to butt the plate agaist. That will prevent any more forward motion.
Jonsel
Not sure what to tell you. I had a plate move a couple of points or two (had to trim them all by hand) just a while back. Not sure what I did wrong. But I think it was maybe because I kicked up the impression a bit too much (?) Maybe I was just making adjustment to the guides or the form and forgot to mark it in the stack.
Normally, yes, on a Patmag the movement would be toward the cylinder. But, like your incident, mine might have moved in the opposing way. Can’t recall now, but that seems likely.
Those plates must have bent a bit downward though when they overhung? Buntings are quite strong and and overhand will bend. I’ve done this before though and just run up material beneath the overhang and that works. If they are moving on you though, it won’t hold them any better I’d imagine.
Can’t think of anything else to resolve your problem especially since you can’t run scrap plate material around the plates, which might otherwise help.
You can have the same problem with polyester-backed plates, plus the possibility of plate stretching, so I am not sure this is the solution either.
If you figure it out, let us know.
Gerald
http://BielerPress.blogspot.com
I’m definitely not looking forward to hand-trimming several thousand postcards. My guess is I overpacked trying to put sufficient impression into the Superfine. Won’t do that again…
j
Just an update: I ran the job again and had better results. I removed one sheet of tympan and worked at keeping a slower pace and that seemed to take care of it. I used the patmag again because it’s the only base I have that fits the whole plate. We did about 500 sheets and didn’t appear to have any movement. The maxim is true: slow and steady wins the race!