This little springloaded pen fits nicely in the 43mm router adapter on your CNC. Replace your Kress router motor with it, on plot away.
It is designed around a 3.2mm ball pen refill. There's a spring for hight compensation (around 13mm diameter). Easy to print, easy to assemble, easy to plot.
There is enough clearance modeled into the parts that everything shout fit nicely, even when using a less than accurate printer