MicroMill

The MicroMill is a 2017 Kickstarter project to promote a small desktop cnc milling machine.

• Kickstarter page: https://www.kickstarter.com/projects/rp3d/the-micromill-a-desktop-cnc-milling-machine/
• MicroMill homepage: http://rp3d.co.uk/

Electronics

The MicroMill is driven by an Arduino UNO (clone) with a Protoneer CNC shield from Protoneer (Ebay). The board is equipped with 3 Stepstick stepper drivers. Only the Z-axis driver has a cooler installed.

Connected are:

• Power supply on Blue screw terminal
• Green button to Resume
• Red button to Abort
• Door to E-Stop
• Yellow wire to SpnEn (single wire on white pin)
• Red/Black wire to 5V/GND (between Blue screw terminal and reset)
• 3 stepper motors (X, Y, Z) to 4-pin connectors next to stepper drivers

Connecting a Probe

According to the GRBL documentation, a probe should be connected to Arduino pin A5:

The G38.2 straight probe and G43.1/49 tool offset g-code commands are now supported. 
A simple probe switch must be connected to the Uno analog pin 5 (normally-open to 
ground). Grbl will report the probe position back to the user when the probing cycle 
detects a pin state change. (https://github.com/grbl/grbl/blob/edge/README.md).
Whatever probe you design should be able to handle some over travel, the Z movement 
likely won't stop immediately. Some sort of spring arrangement would do.

So the probe is anything that will take pin A5 to ground when it touches your object. 
The probe position is relative to machine 0. A typical porbe command might be 
G38.2 X20 Y15 Z-100 (in mm mode). You should set a slow feed rate , e.g. F20 
(20mm/min). The G38 will move to X and Y, then Z axis will lower to -100 until the 
probe makes contact with your object, at which time movement stops. Grbl will 
report the machine position of the probe touch.

https://github.com/grbl/grbl/issues/464

Arduino pin A5 is available as "SCL" on the 8-pin breakout, two pins further is GND, so I attached a 3-pin connector here.