Uneven side to side impression - Heidelberg platen

I have a red ball Heidelberg platen (windmill) that I’ve been using quite successfully for 6 years or so. Last week I noticed that the impression on the right (side guide side) is significantly lighter than just a few inches to the left.

I’m printing with a boxcar deep relief base and polymer plates. The sheet in question is 5.5” wide and 7.5” tall (not that the sheet size matters, but to give you an idea of the area I’m printing, which is a lace pattern roughly half of that sheet size).

I’ve replaced the packing, tympan, cleaned the base, squared the chase - I’ve even replaced the shearing collar just to be on the safe side. Top to bottom impression seems to be normal.

The press has locked up over the years in a minor way a couple times after picking up several sheets, but nothing that would (or has) broken anything. Certainly nothing that I can think of that would move the platen.

I’m totally stumped. Any ideas?

any help is very appreciated. Thanks.


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so…. nothing eh? Kinda surprised.

Only seeing this topic today… didn’t see it earlier.

Do your un-inked impressions show this issue? (To insure it is an impression issue, rather than inking.)

Have you tried flipping the base, or moving it to the left in the chase?