Every now and then I thought about how the CNC machine could be used as a plotter. Of course, the Z-axis, which is driven by a stepper motor, is only conditionally suitable, but at least the positioning accuracy should be clearly superior to the belt-driven plotters. So all that's really missing is a spring-loaded mounting for the pen. This holder is so universal that you can use any pen you like. In a first attempt, I designed a version that accepts a classic Rapidograph (ink pen with capillary nib). But first of all this design was not usable for other pens, furthermore the linear movement was not precise enough.
To solve the problem I got a mini linear rail. This was mounted on parts made of PMMA. I have already used this material in other projects. When heated with a heat gun, it can be bent into shape quite well. The result was already good, but the PMMA was not stable enough. Besides, it is difficult to cut threads in PMMA.
This is how the final version was made. 3 mm thick aluminum is used. It has slots at the appropriate places, which make cold forming relatively easy. The bending radius is therefore very small. The quite large material thickness allows a reasonable use of taps, so that some screw connections can do without nuts.