I have added the tool radius size. The problem is that the Arduino GRBL does not support G41/2. So Dxf2gcode adds the request for compensation, and Grbl ignores it. GRBL on an Arduino cannot do tool compensation, so it will either have to be done elsewhere before loading the Gcode, or I will need to use a different piece of hardware to drive the mechanics - a Raspberry Pi, perhaps, with a different set of code...