We’ve all seen 3D printed jigs that use a permanent marker to color filament as it goes into the hot end. [Sakati84] has a completely different idea. A holder on the print head can pick up one of several pens and use it to color the layer the hot end just laid down. In the video below, it looks like it works well and, although we imagine it will be a bear to calibrate on height, it seems like something you could replicate with nearly any conventional printer.
Logically, you print a layer with no pen in the holder and when you do pick up a pen, it will need to be somewhat lower than the print nozzle or else you’ll drag around in the fresh plastic.
You have to 3D print a rack and some pen holders depending on the brand of pen you want to use. There’s also the holder that fits on the hot end. You can see in the video how the head picks up and releases pens out of the rack. The rack will hold up to six pens.
To switch pens takes a lot of Z axis motion, so we expect print speed is relatively slow in aggregate. There’s talk in the project wiki about increasing Z speed and tips for calibration, but it still isn’t going to be that fast.
For software, there is a Cura postprocessing script. The software thinks there are seven extruders with the first one being for unpainted filament. Extruders 2-7 are virtual and will cause the print to get color after printing each layer.
Overall, this looks like a fun project even if we worry about the health of our Z axis rods. We’ll be interested to see if anyone takes up the challenge to adapt it for other printers.
We’ve played with virtual extruders in a more manual way before. Or, just bite the bullet and add some more real extruders.

Source: https://hackaday.com/2021/07/29/3d-printer-add-on-makes-sharpie-colors/