I am running an old copy of Featurecam V11 from 2003 that came with my Interact and am trying to develop a Post Processor for an ancient lathe controller (Micon 850) - it's basically working but I've had to suspend Circular Interpolation and do everything in small lines as I cannot get my head round the maths involved. According to the controller manual it uses two command lines to set up an arc using the following variables:

Centre of Circle I (=X coord) K (=Z Coord)
Radius of circle R
Angle of target point of arc relative to centre of circle C
Angle of starting point of arc relative to centre of circle C

Command comprises two lines:

N10 G10 Ixx Kzz R(adius) C(start angle)
N20 G02 C(end angle)

Angles are in degrees measured to 0.01 degrees
Angles are measured counter clockwise from the +ve direction of the X axis

Now the Featurecam Xbuild program has loads of mathematical capabilities but I cannot get my head round calculating the right pair of angles for C in the two lines and the radius - everything I do comes out as 90 degrees !!!!

Any help would be much appreciated