HP 7475A Plotter: Refilled Pen Performance

During this plot, an Inmac purple pen (in the Pen 5 slot) pretty much ran out of ink:

HP 7475A - Pen 5 before refill

HP 7475A – Pen 5 before refill

It printed the legend perfectly and started the trace solidly enough, proceeding upward from the far right, but after ten circuits around the center it returned dragging a very faint line behind it.

Ten drops = 0.05 ml of more-or-less reddish purple blended inkjet ink restored its good humor:

HP 7475A - Pen 5 after refill

HP 7475A – Pen 5 after refill

If you get ’em before they fossilize, they’re refillable!


  1. #1 by Jason Doege on 2015-09-10 - 10:05

    Have you tried more aggressive solvents like MEK on the crusted felt?

    • #2 by Ed on 2015-09-10 - 10:48

      Not yet, but another ceramic pen just ran dry and won’t restart: I have a victim on tap.

      I should test the solvents on a dried ink spot to see if they move the pigment / dye / whatever. If the spot doesn’t change, then there’s no point in soaking the nib.

      So many projects, so little time… [grin]

      • #3 by eriklscott on 2015-09-10 - 15:54

        I just got a pen holder for a Cameo Silhouette “craft cutter”. You need a razor blade holder for the 7475A. Then you can use the craft cutter as a 3D printer. Just stack up the laminations and you’re golden.

        It’s about as tedious as it sounds. :-)

        I’m wondering if I’m sick enough to use the pen holder to hold a dremel flex shaft… probably a really bad idea. Probably.

        • #4 by Ed on 2015-09-10 - 20:06

          The Squidwrench Silhouette cutter reminded me of that trusty old HP 7475A… and now here we are.

          a razor blade holder for the 7475A

          Turns out 19 grams of downforce ain’t enough to push the blade through anything, but I sure tried hard to make it so! [sigh]

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