Hello 2D cutter compensation applies only to the diameter (radius/2) of the cutting tool in a plane that is normal (perpendicular) to the tool spindle (ie. XY plane). The information needed to do this is tool relation to the part in direction of cut; LEFT (G41) or RIGHT (G42) or OFF (G40). The amount of compensation is provided at the CNC usually in the D register and can be adjusted at the CNC. It should be noted that a linear move (G1) with both X & Y should be programmed with the cutter compensation block. This move should also be at least as long as the value antisipated in the D register. 2D compensation D register value can represent the full tool diameter, radius or only the difference (trim) between the programmed and the actual tool radius. The program point needs to be the tool contact point for full diameter or radius compensation or the program point needs to be the cutter center point for difference (trim) compensation. Many CNC have refered to 3D compensation but it is really only the same 2D compensation in any plane (not just XY plane). On rotary head muli-axis machines this can be done using G17, G18 and G19 for planes parallel to the machine co-ordinate axis. When planes are not parallel to the machine co-ordinate system a local co-ordinate system can be setup and used with the CNC (G68). Multi-axis (5-axis) machines where the part rotates to bring the part in position to orient the tool axis vector parallel to the machine (tool) spindle has always been able to do 2D compensation in any plane because the tool spindle is fixed in the machines XY plane. True 3D compensaion is required for radius compensation on a 3D surface machining. This can be a requirement in both 3-axis and 5-axis machining. True 3D compensation applies to the tip of the tool and is usually applied to ball end mills. The information required is a surface normal vector supplied by the CAM system at each tool position point (APT GOTO point). This surface normal vector (UVW) is independent of the tool axis vector (I,J,K) and the tool position (XYZ) can be the tip of the ball end mill (XYZ)or more common the center of the ball end mill (XYZ). The actual contact point with the surface is typically not required. The compensation is computed by creating an offset surface by the (constant) distance of the compensation along each surface normal vector. This offset surface is not a linear translation because the curvature is not the same as that of the actual part surface. If the offset surface is away from a concave part surface the radius of curvature will be smaller. If the offset surface is away from a convex part surface the radius of curvature will be larger. This is an easy computation: OffsetX = CenterX + (SurfaceNormalU * CompDistance) OffsetY = CenterY + (SurfaceNormalV * CompDistance) OffsetZ = CenterZ + (SurfaceNormalW * CompDistance) Where: OffsetX, OffsetY & OffsetZ are the compensated tool path points (XYZ) CenterX, CenterY & CenterZ are the programmed center of the ball end mill (XYZ) CompDistance is the compensation distance constant SurfaceNormalU, SurfaceNormalV & SurfaceNormalW are the surface normal vector components (U,V,W) Note that the U.V,W must be the signed components of a unit vector (1.0 unit long) NC4EVER, NCData