[all2]

It has a head designed for fitting writing instruments. I expected some kind of adjustable pressure mechanism, but I'm not seeing it in pictures or in the description. The closest I found was

    The pen holder fits a wide variety of pens, including Sharpie fine and ultra-fine point markers, most rollerball and fountain pens, small-bodied whiteboard markers, and so forth. It can even hold a fountain pen at a proper angle of 45° to the paper. You can also use implements that aren't pens, such as pencils, chalk, charcoal, brushes, and many others. However, you'll get the best results with instruments such as fountain pens and rollerball pens, which do not require the user to apply pressure. 

at [0].

[0] https://shop.evilmadscientist.com/productsmenu/890#

[sleepybrett]

The adjustable mechanisim on the axidraw is nothing but a screw. Essentially there is a right-angled channel you press he pen into and then you tighten a set screw that pushes the pen into the corner.

This design is simple to produce however it causes registration problems if you attempt a multi-pen (multicolor, say) plot, where the pens have different diameters. In the past when faced with this i've 'fattened-up' the narrower pen with tape wraps.