Machine Shop

HP 7475A Plotter: Ceramic-Tip Pen Refill

The ceramic-tip green pen I’ve been using finally ran dry and, having nothing to lose, I tried refilling it.

Grabbing the metal ferrule in the drill press chuck provided enough traction to twist / pull it off, revealing the pen nib assembly inside:

HP 7475A Ceramic-tip pen - ferrule
HP 7475A Ceramic-tip pen – ferrule

A pin vise provided enough traction to remove the nib, which had the expected fiber cylinder extending into the ink reservoir:

HP 7475A Ceramic-tip pen - disassembly
HP 7475A Ceramic-tip pen – disassembly

I injected 0.5 ml of yellow ink from my lifetime supply of bulk inkjet ink (*), then tried to inject 0.5 ml of cyan, which promptly overflowed. In retrospect, allowing a few minutes for the new ink to seep into whatever’s inside the reservoir would be prudent.

After wiping the mess off the pen and reassembling it in reverse order, it works just like new:

HP 7475A Ceramic-tip pen - C-Y refill
HP 7475A Ceramic-tip pen – C-Y refill

During the course of the first plot, the trace went from green to deep blue-green to a different green, which suggests the yellow ink took a while to make its presence known. No problem; whatever comes out of that tip is all good with me.

The stain around the rim of the pen body above the flange suggests a cap that might come off with sufficient persuasion. If it’s firmly fused to the flange, which would make perfect sense, injecting ink through a small hole drilled in the end might produce better results than ripping the nib out yet again.

(*) This leftover came from the never-sufficiently-to-be-damned HP2000C inkjet printer. ‘Nuff said.