My numbers were all wrong ����*
Hello Lisa,
Even when your numbers are incorrect (for the geometric shape you want to describe), using "R" Format Circular Interpolation will result in an arc move being completed successfully, provided that its geometrically possible for the Start and End Points specified to exist on the arc element. However, the resulting arc wont be as you intended it to be.
In any motion control, the trajectory of a circular (arc) move is calculated on the basis of a Centre Point, a Start Point, and the Angular Move between the Start and End Point. When the information relating to a Circular Move in a CNC program is given in terms of Start, End Points and Radius, the control has to calculate the Centre Point of the Arc to use in the generation of the Circular Trajectory. If when writing a CNC program, either the Start Point, End Point, or both are inadvertently specified incorrectly, if its geometrically possible, the Control will simply calculate the Arc Centre based on the data given and then generate the Circular Trajectory for the Incorrect Arc without raising an error.
In your listed program of your first Post, it was geometrically impossible for an Arc to be constructed through the Start/End Points and Radius given and therefore, an alarm was raised. In some way, its fortuitous that your Arc was impossible to create, because small errors when using the "R" Format, Circular Interpolation, often go unnoticed (no alarm raised when its possible to create an arc through incorrect coordinates). If the Arc is only to debur a corner, or as an unimportant blend radius, then it will not matter. However, if a profile containing Radius features is important, then the error may not be pickup until final inspection, or use.
Alternate to the "R" Format Circular Interpolation, is I,J and K Format (I and K for a normal Turning Centre). Using this format, the centre of the Arc is communicated to the control via Vector coordinates from the Start Point to the Arc Centre. If difference in Radius of the Start Point and End Point, relative respectively to the Arc Centre is greater than a tolerance preset in parameters, then an alarm will be raised. Accordingly, a not so obvious error is found before the part is possibly ruined.
Although nothing really wrong with using the "R" format (I choose not to use it), its worthwhile learning how to use the I,J and K Format.
Regards,
Bill