The thing about advises from the internet (likewise this forum) is that it is hard to verify their authenticity. Especially when you are a complete beginner in electronics, like me searching for help on Arduino Uno connection problems. Why: because Easel stopped at the level of Confirm Settings in “Machine Setup”.
A simple way to address the “connection challenge” is to look at the first new generic component, without the complexity of the x-carve or gShield, so this is the Arduino Uno.
I had three different computers at my disposal: MacBook Air (mid 2012 OSX 10.11.2, only USB3.0), iMac (2008 OSX 10.11.2, only USB2.0) and an outdated HP Compaq (Windows 7, only USB2.0). Two of them, HP Compaq and the iMac failed/resist to connect to the Arduino Uno.
Reading through the Inventables and Arduino forum I saw ways to “solve” Arduino Uno problems that proved useless or were unclear to me.
My lessons learned by trial and error: the Arduino Uno connects well with USB 3.0 ports on my MacBook Air but NOT with any USB 2.0 ports on either of the other computers. I cannot explain why, but this is the way it is.
I then followed the instructions to wipe and re-flash the eprom with the Arduino Uno tool on http://Arduino.cc and the procedures on Inventables Community (gbrl) Forum. Why I did this: to make sure the firmware was right.
You can actually see the whole wipe and re-flash process by the blinking LEDs on the Arduino board. Subsequently attach the gShield firmly and check the wiring (really important) once again for loose strands: otherwise the x,y or z carriage will shudder (yes, it happened to me). It operates very well now, without any problems, and likewise in Easel.
For those people unknown to Apple/Mac, the Arduino will not appear as a separate device, like assets in Windows do. In Apple’s Finder, you can find the System Information app: in the Hardware tab, you can find all the USB info. If the Arduino Uno is connected, it is here to see, as it did in my case.
Despite the advise of some others: you do not need a separate 12V/9V Power Adapter for the Arduino Uno, though I have tried that as well. The USB/System Information (Finder) in fact tells how much current is needed and how much is actually current available:
Available current (mA): 1000 (actual read)
Needed current (mA): 100 (actual read)
The USB 3.0 port provides 10 times more current than needed!!!
Hope this wil help others. The x-carve is a wonderful machine.