Drafting Dotting/Lining Pen

Made by a few European drafting tool companies - specifically Dietzgen, Richter, Kern, etc... - these were precision-machined tools used for creating straight lines with different patterns.  This is not the precision-machined vintage German craftsmanship experience.  This is some guy in his basement making a plastic toy to be used with 11mm diameter markers like sharpies.  The model here is approximately 2X the size of the original and it doesn't use a draftsman's liner dip-pen tip to make the marks.  But it works (protip: go slowly and the dots/marks will look much nicer). 

I have included some pattern wheels: a dot pattern, centerline pattern, and phantom line pattern wheel here.  The parts in the images are all made from PLA.  I recommend making the pattern wheels and the arm out of the stiffest material you have.  I have also included a version with a "stabilizer" screw.  It's a little bulky but it removed a lot of the vibration with the PLA parts.  Make sure you print both the "stabilizer" versions of the base and the arm for it to work.  The base is sufficiently thick that it doesn't need any special tricks for rigidity.  The spring is a crapshoot.  I don't know any 3D-printable materials that will apply enough force, won't break, and won't take a set over time in this application.

You will need screws for this and maybe a couple metric taps. I used the following hardware for assembly:

1 - M4 x 12mm flat head socket cap screw 

1 - M4 x 8mm button head socket cap screw (or 2 if using stabilizer version; the stabilizer should probably also have a flat washer "for that extra surface interaction")

2 - M4 x 6mm button head socket cap screw

1 - M3 x 4mm socket head cap screw

1 - M3 x 8mm button head socket cap screw

1 - 1.5mm x 42 or 43mm O-Ring for the o-ring drive wheel (if desired). Should be a tight fit on the wheel. 

This is not an exact scale model of one of these existing pieces.  To make the pattern tighter/smaller the pattern wheel had to increase in diameter and have more lugs meaning the arm geometry had to change to accommodate this.  The originals required a ruler for the drive wheel to ride on.  This just rides on the drawing media.  There is a toothed drive wheel and an o-ring drive wheel.  I've found the toothed wheel doesn't really work well on very hard or smooth surfaces, which is why the O-Ring wheel was created.

I didn't add the FreeCAD file because honestly it's a mess.  I made this as quick and dirty as possible and it takes some understanding to get to printable parts from the original model.  If you want any additional pattern wheels or model changes, let me know in comments. I did include the FreeCAD file for the pen holder so you can adapt to different pens and change the position of the line in relation to the tool edges.