Plate edges making an impression

I’m using Boxcar base and plates. Printing on 110 Lettra, I’m getting some impression from the plate edges into the paper, which is interesting because I’m not pushing very heavy impression.

Just wondering if anyone has an idea for what the problem could be? I’m not getting ink on the plate, but the non-art portions of the plate are making a blind impression on the paper.

I’ve tried using overlays cut close to the size of the artwork. Perhaps trimming the plate closer to the artwork would help? I’ve also tried sanding down the edges to make a graduated slope down to the base, but that hasn’t really done the trick. Maybe need to check that my packing is hard enough?

Thanks for the ideas.

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the plate depth should be deeper than the impression you are trying to achieve maybe. For normal flatbed cylinder work I have been recommended 1.52 for platen presses should be at least this?

Sounds like probably way too much packing. When I print on my Windmill, if it accidentally double-feeds (pulls two sheets at once), sometimes the whole plate will make an impression.

Are you using the correct plate/base combo? If your packing is correct and the plate+base is type high, there’s no way you should be getting an impression from the negative areas of the plate.

Yes, too much impression is what it sounds like; soft packing would cause this if you overpacked because you were gauging it by inspecting the sheet after running a proof, or by feel (as is too often the case).

What is your undercut (if you’re on a cylinder press like a vandercook, commonly .040”) or what depth is your platen set to (commonly .065 for C&P’s for example)?

Been a while since I used 110 lettra, but isn’t it about 15 or 18 points thick? (.015-.018)?

Lastly, how thick is your packing?

Typically, you should have a gauge to measure the packing and the paper thickness, and if you were doing heavy impression you’d probably pack out so that the two- paper thickness and packing thickness- added up to be about .007-.010, depending on how thick your stock is.

The lighter/spongier/more cottony and airy the stock is, the thicker you are able to pack without damaging things, as the stock will ‘compress’ more easily and allow you to push into it further (while this doesn’t neccesarily mean you’re pushing harder).

However, this assumes good hard packing- like oiled tympan sheets, red pressboard, etc; this stuff still compresses down about .001 or so and you ‘lose’ a bit of it as it gets hit with heavy impression.
BUT, when you use soft packing like newsprint or bond paper, it can certainly compress itself and sort of ‘build up’ around the form, especially as you’re adding packing because you’re judging it by feel and/or pulling impressions to examine the physical impression.
(This is NOT the way to do this but many who do not have the proper tools resort to it.)
So as you keep pulling impressions, the packing compresses where the form pushes it in, and you’re left with sort of over-built packing that has a lower area where the ‘print’ is ocurring.
That leaves you with too much packing at the edges of your plate, and so it’s marking your sheet there, as well.

Make sense?

Great ideas and information, thank you.

I’m on a cylinder press, and my packing should be right on at .050-.048” according to the manual.

Yes Jonsel, the plate/base combo should be correct, both coming directly from Boxcar.

Sounds like we’re mostly agreeing that the packing is likely the problem. I am using Sunshine tympan at .006 and .004 undersheets, if I recall correctly. The plan is to grab a micrometer and be a little more exacting using Mark’s numbers as a guide. I do have adjustable cylinder height as well, so I may check the adjustment there.

In any case, I’ll post back with my results in case it will help anyone with a similar problem.

Thanks again to you all for the help.

What kind of press do you have, out of curiosity?

If you are using a cylinder press, the question to ask is not how much packing, but how high over bearers. The bed and cylinder bearers should be even with priniting surface, (assuming correct mounting!). Every thousandth above bearer is what pushes the paper into the form; .003” is normal for a kiss impression, but for heavy impression, it seems breaking the bearings is the effective limit. If you are pushing so far beyond the surface that you are hitting the backing, well, back off.

It’s good that people here are finally geting the idea of the micrometer. But two other basic tools in cylinder presswork are the straightedge and the feeler gauge. Place a good straightedge across your topsheet and insert the feeler gauge between it and the cylinder bearer and you may be surprised how much packing you’ve actually laid on in the quest for a visible impression.

That works if, as I’m sure you do, by straightedge you mean a precision straightedge.
Doing this with just any ruler or tearbar will not work and it’s worth mentioning to those who would try this method.

However, you’d need to engage your packing and a piece of your stock at the same time against the cylinder- the total amount that will go under the cylinder as it prints- for that to work.