The owner of the Reactive Substance web site that makes Grbl shields recommends Arduino Uploader over the standard XLoader. I concur because I was having lockup issues with XLoader. Download Arduino Uploader here:
http://www.ngcoders.com/downloads/ardui … rogrammer/
Also, if you are using the new Uno Arduino (the Omni version), you will need to set the device to m328p and baud rate to 115200. The latter is edited in the small edit window in the app.
I obtained my Arduino chip from Sparkfun and put it into a Duemilanove board and programmed it with Grbl, seems to work ok standalone, haven’t tried it with the shield plugged in because I’m using it for testing. I’m using an Uno board for my actual Shapeoko.