Use Universal GCode Sender to send files to the Arduino.
Update: I have added the kind contribution of Cesar Augusto Fernandez in the form of an easy-to-change-orientation pen-holder. And view-only Onshape files: https://cad.onshape.com/documents/236f46681d1cbe31f6d52db0 (you will need to create an account for being able to export parts to STL).
3d model print parameters
2 nema 17 steppers
4 8mm smooth rods
8 LM8UU
2 GT2 pulleys
10 F623ZZ bearings
1 micro servo SG90
1 Arduino UNO
1 CNCshield
2 Pololu stepsticks...
1 GT2 belt
2 M10 threaded rods
8 M10 nuts
8 30mm M3 screws with nuts
8 6mm M3 bolts
4 M3 washers
2 4mm OD, 100mm-long carbon fiber tubes
2 15mm M3 screws
1 12V 2A power supply
1 USB cable
1 felt tip pen (or many for more fun)