How flat is your ink disc?

When we began printing with this machine (pearl #1) we would get a “bright spot” near the center of the image. It was appreciably better when we replaced the trucks, cores and rollers, but there is still a slight of issue, it is less noticeable with more ink and slim text. It is still showing up (to a keen eye), but not a huge problem. There are two solutions and both are not particularly easy to fix. I was hoping for some input to steer me in the right direction.
I would like to know… how flat is flat. I come from a fine woodworking background and I understand the idea of “dead” flat for the sole of a plane or plane iron. Is that the “flat” that I need to achieve on the ink disc? When I hold a Starrett blade across the disc I am seeing a hair line of light leak (thinner than bond) in the center of the disc, for a perfectly tuned plane that is not flat, but I wonder if that is sufficient for an ink disc. The rollers are new rubber rollers and feel like they would conform (squish) to this, ever so slight, dip
Is there anyone out there that is polishing an ink disc by hand (like a plane) and if you are, what is your stopping point? It is not a huge disc, but I am so not excited about the possible time consuming endeavor. Would surfacing at a machine shop be a proper solution? I can see the circle (edge?) of the stud on the face of the ink disc (like a poor plug weld?). Should I be concerned our ink disc in danger of breaking from the stud, especially if we need to remove material to make it flatter? Please offer any guidance or ideas, I’m sort of stuck.

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It is difficult to tell whether a slight deformation in the ink disk could prove detrimental to your printed image. There are generally some defects, particularly in some of the toable-top presses.

One test would be to roll up ink on a roller while off the press (on a piece of glass, metal or plastic) then put the roller back in the press and make a single cycle of the press. This will let you see if the roller will deflect enough to put an even coating of ink on the disk. If the coating on the disk looks even, then you could assume that your rollers will conform to the disk deformations and not cause problems in your inking of the image.

Try using the side edge of a steel ruler to see if it is in fact bowed. It could also be that the rollers are not bearing down hard enough or (this is unlikely) they are bearing down so hard that the cores are bending.

Knowing a bit about these early Pearls, I would guess that the springs are a bit worn out. Maybe you can add a couple of washers behind the springs where the go on the roller hooks to make them compress more.

Daniel Morris
The Arm Letterpress
Brooklyn, NY

First, you could shim the disk from behind with brass to make better contact with the rollers. If you still getting uneven ink you can bring it to a machinist/fabricator.

If the disk is relatively thick, say 3/8” you can have the disk ground then polished. This would cost you anywhere from $90-$150 depending on who you take it too.

You could lap the disk yourself if you have access to a levigater and some grit. Most university printshops are setup for a similar process to grind litho stones and they might let you give it a shot. I have used this method myself, but it took 10 hours and a lot of sweat to grind a couple of micro meters.

Lastly, before you go any further, remember your problem could be caused by a combination of factors. One thing to check is your inking methods and humidity factor.