Summary

This is a pen plotter addon for your Anycubic i3 Mega printer.
I have tested it extensively and it seems to work fine without further modification.
The current setup also allows for quick disassembly, so you can easily switch between standard 3D printing and the plotter setup without much hassle.

Additional required nonprintable components:

For this addon you will need 2 rods with a smooth surface (wood/metal/etc.)

Required measurments for rods:

lenght: 43 - 44 mm
diameter: 5,8 - 6,0 mm

You will also need a rubber band.

(exact dimentions needed may vary slightly depending on printing tolerances)

If needed, 3D model can be more or less easily modified in CAD before printing or even after printing.

Installation:
Install the upper mount using existing screws on print head cover.
Insert rods. Depending on the quality of the printed parts, glue may be required.
Mount the pen holder and the lower mount as seen in the pictures.
attach rubber band to lower mount and pen holder using the attachment hooks on both parts.

The order in which the parts are assembled may vary.