Marty, I think what you need is to export your .SVG as a .DXF. I'm also going to be working with a similar machinist who can take a CAD file and use it to guide a flo-jet machine. AutoCAD can read a .DXF file and this format may in fact be the prefferred one by your guy. The shop I'm working with specifically asked for a .DXF file.

Just open your mask in Inkscape and go to Save As and select .DXF from the dropdown. Hope that helps.