I can't tell you how the machine is set up because i am just the programmer of the application which converts plt files into gcode.A axis rotates the knife. I run demo version of mach3 and got xml from machine manufacturer. however, even on my pc which is not connected to anything i see that speed varies( label units/min. ). Meybe it is because of the changing direction of the movement? even if i round the corner and movement should be smooth, i observe dramaticac speed changes.
edit:
i think the reason why A axis is not associated with pins is that my pc is not connected and xml is from my pc, not the one from the plotter.