Definition of terms

The following terms are briefly explained:

Polynomial contouring:

Curvature and direction-continuous connection of two motion blocks.

Contouring curve:

Curve composed of two 4th order polynomials per axis.

Block length:

The path length of the curve corresponding to the motion block.

Corner distance:

Distance from the start/end of the contouring curve to the programmed target point/starting point of a motion block (see figure below). The corner distance is always limited to half the block length. In a circular block, the corner distance is the arc length from the starting point of the contouring curve up to the programmed target point of the arc.

Definition of corner distance
Definition of corner distance


Motion block before the contouring curve


Motion block after the contouring curve


Corner distance of the pre-block


Corner distance of the post-block

Interim point:

Point at which the two partial curves of the contouring curve meet.

Corner deviation:

The distance between the programmed corner point and the interim point of the contouring curve (see figure below).

Definition of corner deviation
Definition of corner deviation

Programing Example


Comparing the programming of G61 – G261/G260

The 3 NC programs all generate the identical contour shown in the figure below.


N10  X0   Y0 G01 F1000

N20  X20  Y100

N30  G61  X40 Y100

N40  G61  X60 Y20

N50  G61  X80 Y20

N60  G61  X100 Y100

N70  X120 Y100

N80  X140 Y20

N90  X160 Y20

N100 M30


N10  X0   Y0 G01 F1000

N20  X20  Y100

N30  G261 X40 Y100

N40  X60  Y20

N50  X80  Y20

N60  X100 Y100

N70  G260 X120 Y100

N80  X140 Y20

N90  X160 Y20

N100 M30


N10 X0   Y0 G01 F1000

N20 X20  Y100

N25 G261

N30 X40  Y100

N40 X60  Y20

N50 X80  Y20

N60 X100 Y100

N70 X120 Y100

N75 G260

N80 X140 Y20

Contour from programming G61 – G261/G260
Contour from programming G61 – G261/G260