Helical interpolation

The helical interpolation is a superimposition of a circular interpolation (plane of the 1. and 2. main axes) and a linear movement in the 3. main axis. The resulting screw-shaped movement (helix) will be executed with a constant pitch. The pitch will be programmed by the third parameter of the circular interpolation dependent on the selected plane.

Syntax example for plane G17:

G02 | G03X<expr>Y<expr>Z<expr>I<expr>J<expr> | R<expr>K<expr>

G02 | G03 Circular interpolation CW / CCW

X<expr> Y<expr> Target point in plane XY

Z<expr> Target point on the helical axis perpendicular to plane XY

I<expr> J <expr> Position of the circle center point of the interpolation in plane XY
(I in X, J in Y), corresponding to G161/G162.

R<expr> Radius of the circle to be interpolated (alternative to I,J)

K<expr> Helix pitch in Z (value generally unsigned)

Syntax corresponding to the selected interpolation plane:

It is not necessary to define the pitch in a way, that the helix exactly reaches the programmed target point. In such cases the NC-Kernel calculates under consideration of the fixed positions of start- and target point a "corrected" pitch, which is approximated as close as possible to the programmed pitch.

For this based on the programmed pitch the target point of the helix will be calculated at first. If this calculated target point differs from the programmed target point, a correction will be necessary. The criteria for the correction is the distance between the programmed target point and the calculated target point saw in direction of rotation.

If the distance is smaller or equal π(180°), the target point of the helix will be moved on the programmed target point contrary to the direction of rotation. So this means the pitch will be increased.

If the distance is more than π(180°), the target point of the helix will be moved on the programmed target point in the direction of rotation. So this means the pitch will be decreased.

Correction of the helix pitch dependent on the direction of rotation

Example 1:

Principal correction of a helix clockwise (G02).

Case 1:

The target point calculated with the programmed pitch P_prog is within the area of 180° degree behind the programmed target point (saw in direction of rotation). For correction the pitch P_korr must be increased.

Case 2:

The target point calculated with the programmed pitch P_prog is within the area of 180° degree before the programmed target point (saw in direction of rotation). For correction the pitch P_korr must be decreased.

Example 2:

Helical interpolation clockwise in plane XY with following helix:

Starting point a: X-10 Y0 Z0

Target point b: X0 Y-10 Z-20

Helix center I, J: zero point

Helix pitch K: variable

: 
N10 G17 G90 X-10 Y0 Z0 F500 
N20 G02 X0 Y-10 Z-20 I0 J0 K.. 
: 

Minimum rotation: ¾ -> pitch K=26,66

Pitch K ≥ 26,66:

The helix from a to b will generally be executed in ¾ rotation, because the correction is limited to the maximum possible pitch K = 26,66.

Pitch K < 26,666: