Function G2(StartX, StartY, EndX, EndY, Radius)

Thanks Ross. That looks like the math I was looking for. I'll see if I can work out the code and post it here.
There are two instructions in Gcode for cutting an arc one is
G2 Clockwise and and G3 Counter Clockwise. those commands
take even less parameters than the function I was looking
at. They would look something like this.
G2 5 5 2.5
what it does is takes the current position of the cutter and
cuts and arc to coord 5,5 with a circle radius of 2.5

This cuts a circle

G01 Z 0.2 F5 (retract)
G01 X1.5 Y1.135 (move to starting point)
G01 Z-0.5 F5 (plung)
G03 X 1.865 Y 1.500 R 0.365 F10 (quadrant 1)
G03 X 1.500 Y 1.865 R 0.365 F10 (quadrant 2)
G03 X 1.135 Y 1.500 R 0.365 F10 (quadrant 3)
G03 X 1.500 Y 1.135 R 0.365 F10 (quadrant 4)
G00 Z 0.2 (retract)

http://xdobs.com/cnc/gcode-introduction.html

Thanks again