Uneven inking on C&P

Hi, hoping I can get some help. I’m printing on a 10x15 C&P, three rollers, motor-run, using a boxcar base and magnetic polymer plates. I am not the only printer who uses this press, and have been able to print with the same plates in the past with no issue. Now, I must pack the plate itself for the rollers to ink the surface at all, and it does so inconsistently. There is no tape on the tracks, and the chase seems to be level. The plate impression on the paper is even. Any suggestions to fix this?

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Three thoughts:

(1) Are you sure the base + polymer height is .918? Boxcar is for adhesive-backed plates, not magnetic. Boxcar makes two thicknesses of bases, and there are many different plate thicknesses.

(2) Check that there is no tape on the rails, and no tape on the trucks.

(3) Rollers can shrink as they age. Confirm that your rollers are the same (or larger) diameter as the trucks.

Any one of the three issues above can affect the ability of the rollers to ink the plate.

Kelly

could be your base + plate isnt type high. Underlay the base (between it and the bed) until the plate inks well, then adjust packing for impression

I mistakenly ordered the wrong thickness of polymer plate recently. I had planned to put some packing under the base it if I have any problems with inking as that worked when I had this issue with a wood block. It is comforting to know that someone else has had this problem.

Could someone have changed the trucks? If the trucks were old and worn they would have allowed the rollers to run lower to ink the form and if they got replaced with new trucks the rollers would run higher in relation to the form.
Something to check.
Bruce

I think everyone above mentioned most of the crucial points to troubleshoot, but I tried to think of more things for you to check:
1- Is your packing and tympan fresh and the right - thickness? Because if it is already overused it might result in uneven pressure.

2- Are you using good furniture? Sometimes the setup “arches” upwards when you tighten the quoins if the furniture is wooden or bad quality.

3- Are the rollers getting properly inked from the rotating inking plate? Since you said blind pressure is good on the sheet of paper maybe you want to check if the rollers are getting the proper ink to begin with before even reaching the plate.

That being said maybe you want to try and let the machine ink the plate and before printing remove the chase and try to handprint a sheet using the backside of a wooden cooking spoon over and over on top of the paper over the plate. If the print is evenly inked then you have one of two problems; the height of the plate relief (try different plate thicknesses) or the packing underneath the tympan (repack a fresh tympan and give it a try)

I hope this helps and good luck!

Shadi Ayoub
the961collective