My version of a common type of pen holder for CNC mills. No need to remove your router/spindle as this will fit in the collet. Will work with different diameter pens.
Currently two versions, one for a 1/4" shank and the other for a 1/8" shank.
I tried a couple different orientations, and it prints pretty well without supports.
Aluminum (or other) rod with shank diameter, cut to length.
Two shaft collars for rod.
Compression spring - I used a 7/32" for the 1/8" shank and a 3/8" for 1/4"
A couple of M3 screws to secure pen.