Dan,
how the coordinate system on a XY table actually works
Depends on how you have your machine setup. You can set your 0,0,0 anywhere you want.
Have a read of the Mach Mill manual.
software produces the g-code with coordinates
In general the software will look at the dxf, it contains the location of all the entities which you have
drawn and extracts that data on import. Best example is to save a file as a ver 12 DXF and look at the
file with Notepad since it's a text file. You can't do that with later dxf versions and they will contain additional
info on what was contained in dxf ie; the third axis locations etc. In general you now must define what you
want to do with each entity that was drawn, no software is a "mindreader".
will the circle at the end actually be 10cm diameter
Well it depends if the program used outputs the file as vectors based on precise data or as vectors
based on screen pixels/units, whatever. You want to use a vector based CAD drawing program and
will remark that not all programs generate dxf's exactly the same and some are just outright terrible at it.
[qoute]how do you calculate how many steps per mm the machine is[/quote]
Try the calculator in Members Docs or use the axis calibrator in Mach to check.
http://www.machsupport.com/forum/index.php/topic,16315.msg110286.html#msg110286Can you post your DXF file of what you have drawn?
RICH