Here is the updated Tool-/Penholder for the 2020 Drawbot Drawing Robot.
The servo version works great, but it is loud and a bit unflexible.
Now I use a cheap 28BYJ-48 stepper motor to move the Z-Axis up to 42mm.
Version 2 is more flexible and you can change the penholder to what ever you like (cutter, mill...)

VERSION 2: with bolt on penholder

HARDWARE:
2 X 95mm x 3mm rods (Z-Slider)
2 X 50mm x 3mm rods (flexible penholder)
4 X 8mm x 3mm pins (to fix the rack + super glue)
1 X ballpoint pen spring
6 X M3 x 8mm screws + nuts
1 x M3 x 20 to 30mm + nuts

SOFTWARE:

• GRBL V1.1h: https://github.com/gnea/grbl/releases
• Universal G-Coad Sender (UGS): https://winder.github.io/ugs_website/download/
• Inkscape : https://inkscape.org/release/inkscape-1.1.1/
• Hatch Fill: https://github.com/dapperfu/inkscape_HatchFill2

ELECTRONICS for the Z-Axis:

• DRV8825 driver set to 8 microsteps or equal
• Vref =0,108V (depending on you stepper driver)
  1 X 28BYJ-48 stepper (modified to run on CNC shield)

How to ...

28BYJ-48 stepper modification:
To get it run on the CNC shield, you have to change the wires in the plug. The red wire is not longer needed (I does't matter if you cut it or leave it unpliged) chnage the wires like:

https://www.youtube.com/watch?v=kCDGEezyzfw

Assembling the Z-Axis Toolholder:

1. Fix the rack with the 8mm pins and with super glue to the slider plate and use 4 nuts.
   

2. Screw the stepper motor on the rear plate loose, not fixed and add the gear.
   

3. Ensure, that the 3mm rods are sliding easy in the holes (I used a 3mm drill to make it). Add the slider plate to the rear plate and fix it with the rods.
   Now agline the stepper and fix it.

4. Carry on with the penholder, add the spring to the penholder and ensure that the sliding worke well and easy.
   

5. You can bold on the penholder to the sliding plate. to reach the lower screws just slide the penholder up.

6. Now screwe on the complete Z-Axis to the plotter and connect the wires.
   My stepper driver DRV8825 is set to 1/8 microstepping (jumpers M0 and M1 connected) and Vref is set to Vref=0.108V.

Installing Software:

• Upload GRBL to the arduino, start UGS (Ultimate G-code Sender) and connect your drawbot.

Inkscape Tutorial G-Code for a 3Axis Drawbot

https://youtu.be/VZizexI1GDs