Uneven Impression

I am beginning to set up my first ever letterpress job. I think I bit off more than I can chew doing a complete wedding invitation package.
I am working on a Kelsey Model O 5x8 letterpress.
When I try to test out my polymer plates on my paper, no ink yet, I see that my impression is uneven. An impression shows at the bottom of paper and less at the top. I am a bit nervous about touching the screws in the back of the platen but I think that is where I begin to adjust that problem. Is that correct?
Is there anyone is the South Jersey area that has experience with a tabletop letterpress and its workings?

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Generally if the bottom of the print is heavier than the top the amount of packing on the platen needs to be reduced so that when the platen closes it is parallel to the plate. Ideally the platen packing should be about 40 thou in thickness including the stock you wish to print but that figure can vary with the type of machine - hope this helps

Thank you, Frank. I am going to check my packing. I thought I tried it with and without packing but maybe not. I appreciate the help.

As Frank stated if the print is heavy at the bottom remove some of the packing sheets until you get a good print.

If it is still lighter at the top then you make adjustment in the packing by creating a paper wedge, pasting strips of paper on one of the packing sheets with more strips at the top.

Once a press is set there shouldn’t be any need to touch the platen bolts/ screws, all adjustment is done in the packing and by make ready.

@platenprinter, How do you know your platen bolts are set right? I have a 6x10 tabletop that I got from someone whose family member had used it years ago. They didn’t know letterpress printing and I am just starting out. I messed around with the bolts during cleaning and my first attempts at printing. So how do I set them correctly so I can rule that out in the future and know that I only need to adjust my packing? Thank you for your advice!

”Only need to adjust my packing” Now if you have a platen press that works like a clam shell, then when changing from thin paper to thick card or vice versa you will always need to tweak the bolt settings just a little. Parallel approach platens not so, packings to suit the job and the paper only.