Conversion of Arcs from R to IJK

The Convert Arcs R to IJK function replaces circular interpolation commands G02 / G03 with a radius parameter R by equivalent commands with absolute arc center coordinates I, J or K, depending on the active plane (G17, G18, G19). This format is preferred by many post-processors and controllers, especially for complex or large arcs. NCPlayer supports two conversion modes: Convert R arcs → IJK (Incremental) and Convert R arcs → IJK (Absolute).

What the function does

• Scans the NC program for all G02 / G03 commands with the R parameter.
• Determines the current machining plane:
  • G17 — uses I and J (Z-axis as perpendicular).
  • G18 — uses I and K (Y-axis as perpendicular).
  • G19 — uses J and K (X-axis as perpendicular).
• Calculates the arc center coordinates in the absolute system based on:
  • The previous endpoint (arc start point).
  • The new arc endpoint coordinates.
  • Arc direction (CW/CCW).
  • Sign of the radius R (minor or major segment).
• Replaces R with the calculated I, J, K.
• Keeps comments and other line parameters unchanged.
• Does not modify commands containing G7x, G8x, G10, or lines that are comments.

Algorithm (short version)

1. Read the file line by line, determine the current working plane (G17, G18, G19).
2. If the line contains G02 or G03 with an R parameter — extract all coordinates (X/Y/Z).
3. Calculate the arc center using geometric formulas depending on the plane and direction.
4. Form a new command with I, J, K instead of R.
5. Update the current position (arc endpoint becomes the new base point).

Examples

; Before:
G17
N10 G02 X50 Y50 R25 F200
N20 G03 X0  Y0  R25

; After:
G17
N10 G02 X50 Y50 I0  J25 F200
N20 G03 X0  Y0  I-25 J0

When to use

• If the machine controller does not support the R parameter for arcs.
• When preparing programs for CAM systems or simulators that require explicit arc center coordinates.
• To avoid ambiguity when handling large arcs (> 180°).