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HP 7475A Plotter: Inmac Ball-Point Pen Tweakage

The big bag o’ new-old-stock Inmac ball-point plotter pens had five different colors, so I popped a black ceramic tip pen in Slot 0 and ran off Yet Another Superformula Demo Plot:

HP 7475A - Inmac ball pens - weak blue

HP 7475A – Inmac ball pens – weak blue

All the ball pens produce spidery lines, but the blue pen seemed intermittent. Another blue pen from the bag behaved the same way, so I pulled the tip outward and tucked a wrap of fine copper wire underneath. You can see the wire peeking out at about 5 o’clock, with the end at 3-ish:

HP 7475A - Inmac ball pen - wire spacer

HP 7475A – Inmac ball pen – wire spacer

The wire holds the tip slightly further away from the locating flange and, presumably, makes it press slightly harder against the paper:

HP 7475A - Inmac ball pen - stock vs. extended

HP 7475A – Inmac ball pen – stock vs. extended

A bit more pressure helped, but not enough to make it dependable, particularly during startup on the legend characters:

HP 7475A - Inmac ball pens - extended blue

HP 7475A – Inmac ball pens – extended blue

That black line comes from an ordinary fiber-tip pen that looks like a crayon on a paper towel by comparison with the hair-fine ball point lines.

Delicacy doesn’t count for much in these plots, so I’ll save the ball pens for special occasions. If, that is, I can think of any…

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