Inconsistent impression from - 6x10” tabletop platen press

Think of the closing platen as like closing a book. If you add to the height of either side, bed or platen, they touch before they are parallel and if you reduce the packing they close so they touch after they are parallel. Parallel at the moment of pressure is what you want, and that is why it is important to adjust the platen so that the kind of impression you want (sounds like you are trying for deep impression) occurs just when the platen is exactly parallel to the bed. Adding packing makes that contact occur sooner, so reducing packing will help level things out, but it may also mean you don’t get the impression depth you want. If you are able, pull the chase and add a little packing as a full sheet behind it, taped to the chase. If the impression is even but not heavy enough adding shims behind the chase moves the chase out but still parallel to the bed, and still parallel to the platen at the moment of impression, and increases the pressure.

Also, ideally your press has an impression stop built into the bar “toggle” behind the press. You should always hit that impression stop when you are printing, for consistent results, and you adjust the impression so the result obtained at the impression stop is what you want. If you are not hitting the stop each time every print will have slightly different pressure.

To add to adlib’s comment on the book analogy, if you add a bunch of layers, the book won’t close because of the jamming near the spine. If you take All of the pages out, the book closes with the right edges touching, but a gap at the spine. This is a drawback of a clamshell design.
The platen should be adjusted to the packing you want to use. If you want a deeper impression, then a softer top sheet or packing is needed.

To add to adlib’s comment on the book analogy, if you add a bunch of layers, the book won’t close because of the jamming near the spine. If you take All of the pages out, the book closes with the right edges touching, but a gap at the spine. This is a drawback of a clamshell design.
The platen should be adjusted to the packing you want to use. If you want a deeper impression, then a softer top sheet or packing is needed.

Also, for Pearl and similar press users, the surviving population of Pearls has been significantly reduced by printers trying to do deep impression on them - it usually breaks the frame at the platen pivot bearing. My Pearl had that “accident” and was repaired, but the platen had been damaged by too much stress. The second Pearl I got with the repaired one had been broken that way also so I “robbed” the platen from it to replace the other damaged one. “Frankenpress!” I had to buy two Pearls to get one useable one.

@Adlibpress and @ericm, Thank you so much for this! The book analogy really helped me better visualize the problem. I tried adding a piece of paper behind the chase and I removed all packing from the platen save one sheet. This has given me the best impression I’ve gotten yet, pictured here.

Generally, I do like a bit of a deeper impression, but I’d be over the moon to get anything that’s evenly printed onto paper right now.

IMG_7612.jpeg

Presses are just weird. They have their “personalities”. One job will need “This”, another job will need “That”. On larger area jobs, as in your pic, you will have to “Spot” maker easy. Hit a sheet, then, adding pressure to the light areas. This sheet needs to be thin. .003” - .005” thick. Slip this under your platen plate, or whatever base layer you are using. Use thin stock to build up pressure as you want built up areas to be very gradual in height change.

Well are they wierd or is it more a case of them being precision pieces of engineering. The basis is printing from type or cuts with a printing height of 0.918 inches (UK & USA) and key is to ensure that type and cuts is checked for this height. Packing is the next most important aspect. Many presses will carry a packing thickness of 0.040 to 0.050 thousandths of an inch. This will give you a packing of maybe 2 sheets of ivory card, 4 or 5 sheets of a super calendared paper and a top tympan sheet. By having this kind of selection it is easy to adjust for the stock being used. One last thing to remember is that all the old presses were never intended for deep impression and for some of the smaller hand presses, deep impression will damage the machine.