Axis of helix 3D path along axis
The screw curve is built around the axis of the helix. Axis can be either straight or curved.
Straight axis can be defined by two 3D points: the start and end. 3D points can be defined by 3D nodes, as well as by any 3D object that can determine a point in space. The vector defining the axis of the helix will be directed from the first point to the second (respectively, the beginning and the end will be determined). The shape of the curve is determined by the parameters of the helix 3D path.
1  First point of axis 2  Second point of axis 3  Axis 4  Screw curve 
Curved axis can be defined by 3D paths, 3D profiles, loops, edges. Multiple selection is also acceptable if selected object form a tangency continuous contour. Contour could be either open or closed.
Selecting a closed axis yields a closed 3D path by default.
There are limitations applied to constructing a closed helix 3D path. Radius/diameter should have the same value in the end and in the start of the screw curve. X_tan parameter values in the starting and ending points of the pitch graph should be higher than zero.
Closed helix 3D path constructed using a pitch graph
Manually apply the desired length, if you need to create an open path by a closed axis. Limitations mentioned above are not applicable to open paths created by closed axes.
Main parameters of helix 3D path along axis
The appearance of the resulting helix 3D path resulting from this operation is determined by the following parameters:
•Radius/diameter
A cylindrical helix (i.e. the one with constant radius/diameter along the whole length) is created by default. It is possible to set different values for starting and ending radius/diameter. Then it will change linearly from start to end value along the helix length. Another option is to use graph of dependency between radius and length.
•Start angle and start point
Define the initial point of screw curve (see below).
•Direction of coiling
The clockwise direction (when looking along the helix's axis) is applied by default. It can be switched to counterclockwise if necessary.
•Pitch, length and number of coils
The helix can be defined using one of the following parameters combination: Length and Coils, Length and Pitch, Pitch and Coils.
The third parameter is calculated automatically from the values of two others. By default, an axis's length is used as a helix's length. It can be changed to a custom value if necessary.
When using the Length and Pitch combination, the pitch can be defined either by a constant value or by a graph in dependency to length.
Length of screw curve is defined by distance between 3D nodes that define axis (additionally, pitch is defined) 
Length of screw curve is defined by pitch value and number of coils (n = 4)

Initial Point of Screw Curve of Helix 3D Path along axis
By default, the initial point of the screw curve is chosen arbitrarily by the system. It can be changed by setting the desired position using an additional 3D point  the start point. Additionally, you can specify the numerical value of the start angle of the screw curve's initial point rotation.
1  Axis 2  Default initial point of screw curve 
When you specify the start point, the initial point of the screw curve will move along the specified initial radius to the plane passing through the selected point and the axis of the helix 3D path.
1  Selected start point 2  Plane passing through axis and start point 3  Initial point of screw curve 
When simultaneously setting the start point and the numerical value of the start angle, the angle is measured from the plane, passing through helix's axis and the start point.
Initial point of screw curve is defined by numerical value of start angle (30°) without selecting start point 
Initial point of screw curve is defined by start point and numerical value of start angle (30°) 
Using start point for defining radius/diameter
Selecting a start point and disabling the start radius/diameter's checkbox links screw curve's radius/diameter to the start point's position.
Radius/diameter of screw curve is defined by start point 