SP-20 inking problem

I’m printing a very large plate of a linear illustration. The poster size is 18×24 and the plate is almost that size. I’m using my SP-20. The problem I’m having is, right in the middle of the form, I’m not getting solid ink coverage. It’s almost exactly in the center. My rollers are only 4 years old, although I suppose it’s possible they have shrunk a little. To get the middle to ink properly, I’ve had to really lower the rollers. The problem with that is then the ink coverage is so heavy on all 4 sides that it looks like crap and is slurring off and building up on the edges. Not good. I’m not sure what to do. The illustration is all connected lines, so I can’t pull out a piece and print in a second pass.

To make matters more fun, I’m running a 3-color split fountain. I was thinking of running the colors separately. Would they blend properly? The issue would still remain with the very center of the poster, as the middle color is very heavy on the leading and end of the sheet, but too light in the very middle. I just don’t know how to compensate for this. It doesn’t seem as if makeready on the packing would solve it as impression is fine.

I should also add that I can’t just pull up the plate and add some paper behind that section. It’s mounted on a wood board. If I pull it up, tons of little pieces of the wood come with it and that’d be it for the plate.


4 thoughts on “SP-20 inking problem

  1. Jonathan Selikoff - December 17, 2015

    I exclusively use mineral spirits for wash up. Maybe that’s bad?

    The plates are commercially produced but the board is a large fine chipboard panel from Home Depot. I continually struggle with these large plates as I have to shim them to type high with a lot of chipboard and other papers. I’d love to find a source of nearly type high wood that I can mount plates on. I can’t afford a boxcar base of that size, although that would probably solve a lot of my problems.

    As I check the panel flat on the bed, there is a little movement from left to right corner, so that may account for some of the problems as well. I tried to fix it in as tightly as possible with quoins to minimize the movement, but it didn’t solve it all. To get by, I double and triple rolled the form to make sure enough ink was on the plate.

  2. Paul Moxon, Moderator - December 17, 2015

    That’s true, Katie. I neglected to ask whether the plate is a commercially produced magnesium or copper plate, or a homemade polymer and wood combination. MFD (medium density fiberboard) has the greatest uniformity, but still has a .0005″ tolerance. Jonathan?

  3. Katie Harper - December 17, 2015

    Couldn’t this also be caused by a slightly warped wood base? It’s very difficult to get a large wood base to be planed to a consistent height over its entire area. I would try printing another form (with one ink for the test), something small that you know to be type high (consistently), something you could move around to different positions on the bed. Then see if you are still getting variations in inking. If the rollers are bad, you should see uneven inking in the parts of the form under those bad spots. If you don’t see this, then perhaps the form (plate mounted on wood) is the issue.

  4. Paul Moxon, Moderator - December 16, 2015

    Jonathan, you know what the answer is: new rollers. Yours seem to be out of shape. Splitting a fountain job won’t work for critical jobs. Hard to say, why they haven’t lasted. Too much fluorescent light or sunlight, wrong solvent.

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