G02 and G03 are how you cut curves. They are a feed move like G01, but instead of a straight line they trace an arc. The single thing that separates them is direction.

G02: clockwise

G02 cuts a clockwise circular interpolation. G03 cuts a counterclockwise one. The catch for beginners is “clockwise from where?” The convention is to view the arc looking down the positive axis perpendicular to the active plane. In the default G17 XY plane, that means looking down from positive Z onto the table, the way you normally stand over a mill.

Defining the arc

Both codes need a feedrate and a way to describe the curve. There are two ways:

  • I, J, K: the distance from the arc start to the arc center, along X, Y, and Z.
  • R: the radius of the arc.
G02 X20 Y0 R10 F150   (clockwise arc to X20 Y0, radius 10)
G03 X20 Y0 R10 F150   (same endpoints, the other way around)

Notice the endpoints can be identical. Only the code changes the path. That is exactly why a swapped digit produces a part that is wrong in a way that is hard to spot on paper.

Why beginners reverse them

Clockwise and counterclockwise are abstract until you fix the viewing direction, and the plane can change with G18 or G19. Beginners also tend to learn G02 and G03 from a static diagram, which builds recognition but not recall. When the arc is in your head instead of on the page, the direction slips.

A memory hook some students like: G02, the 2 looks like it curves over to the right (clockwise); G03, the 3 has its bumps opening the other way. Use whatever sticks, then drill it.

Lock it in

Treat G02 and G03 the way you treat G00 vs G01: as a pair to practice directly until the right answer is instant. Both are core entries on the list of common G-codes for CNC beginners, and direction recall is exactly the kind of thing the practice-first method is built to fix.

Bottom line

G02 is clockwise, G03 is counterclockwise, judged looking down the axis normal to the active plane. Same endpoints, opposite curves, so drill the direction until you never hesitate.

G-Code Sprint is a study and practice tool only. Always follow your instructor, employer, machine manual, and shop safety procedures.