Quote Originally Posted by Desertboy View Post
The Arduino should power up from USB socket (It's 5v) and then wire your 24v power supply directly to the cnc shield, if you don't have a 24v power supply get one. If you are using 4 motors (2 for the lower axis) use all 4 axis on the cnc shield and set one of the axis as a clone so you can get the maximum out of your nemas.

First question is have you tried the uno without the cnc shield on it?

Arduino can only handle 5v if you pump 12v or above into the Uno you will fry it! The CNC shield is designed to pass power from the onboard power socket to the stepper drivers bypassing the Arduino. The arduino is powered by the USB socket or optionally the 5v plug on the Arduino board which is more for standalone arduino operations.

grbl is actually very good

Check out this page
http://www.instructables.com/id/3020...CNC-Shield-V3/

I found it useful although a lot doesn't apply to me.
Hi,
As I mentioned I'm coming from the 3D printing world. The motherboards I use feed the Arduino via a built in step-down; that's why I couldn't be too sure and couldn't find a decent PCB trace schematic.
But thank you, that answers my question!
My shield is already set up like so, I've already loaded up GRBL and was just connecting up everything for a first test.

Compared with 3D printing (and keeping in mind I built my own printer) I find the mechanics on CNC more challenging due to the greater forces involved but the electronics tend to be easier! (Mainly because they're less developed at this point, sadly).