Circular Interpolation Techniques: Advanced G90/G91 Programming with CNC Examples

5nd part of Circular Interpolation Concepts & Programming series, this article explains Use of

• G90 Absolute Programming
• G91 Incremental Programming

with cnc program examples code explaining both G90/G91

Read Other Parts of this Article

• Circular Interpolation Concepts & Programming Part 1 (Concepts)
• Circular Interpolation Concepts & Programming Part 2 (Use of R)
• Circular Interpolation Concepts & Programming Part 3 (Use of I J K)
• Circular Interpolation Concepts & Programming Part 4 (Unknown R)
• Circular Interpolation Concepts & Programming Part 5 (Examples)
• Circular Interpolation Concepts & Programming Part 6 (Uses & Exercises)

Circular Interpolation using G90 and G91

• G90 X ____ Y____ defines the arc end point in the work co-ordinate system.
• G91 X_____ Y____ defines the signed distance of the arc end point from the arc start point
• I____ J____ defines the signed distance of the arc start point from the center point of the arc

For example: see the following picture.

Circular Interpolation using G90 and G91

Example CNC Programs

G41 G90 G01 X0 Y20
G02 X10 Y30 I10 J0
G01 X20 Y30
G01 X20 Y40
G02 X30 Y50 I10 J0
G01 X45 Y50
G02 X50 Y45 I0 J-5
G01 X50 Y5
G02 X40 Y0 I-13.59 J14.68
G01 X0 Y0

G41 G91 G01 X0 Y20
G02 X10 Y10 I10 J0
G01 X10 Y0
G01 X0 Y10
G02 X10 Y10 I10 J0
G01 X15 Y0
G02 X5 Y-5 I0 J-5
G01 X0 Y-40
G02 X-10 Y-5 I-13.59 J14.68
G01 X-40 Y0

Circular interpolation is quite a bit more demanding on your machine as two axes have to be precisely coordinated. Drawing a complete circle involves not just coordinated motion but reversal of direction at each of the 4 quadrant points. These would be the points corresponding to 0, 90, 180, and 270 degrees.

Read Other Parts of this Article

• Circular Interpolation Concepts & Programming Part 1 (Concepts)
• Circular Interpolation Concepts & Programming Part 2 (Use of R)
• Circular Interpolation Concepts & Programming Part 3 (Use of I J K)
• Circular Interpolation Concepts & Programming Part 4 (Unknown R)
• Circular Interpolation Concepts & Programming Part 5 (Examples)
• Circular Interpolation Concepts & Programming Part 6 (Uses & Exercises)