Help plz - 3D modeling helical / helix pipe system transitioning to vertical runs.
In the following I have created a helix with a radius of 1, a height of 3 and 3 turns. The helix's base is at 0,0,0. The green line is from 0,0,0 to the bottom end of the helix. The yellow line (its length is not important) lies on the XY plane, is perpendicular to the green line and has an end at the end of the helix.
We want the yellow line to have the same slope as the helix. We can compute the slope angle (theta) via:
theta = asin( pitch/(sqrt( (2*pi*r)^2 + (pitch)^2) ))
Note, sqrt( (2*pi*r)^2 + (pitch)^2) is the length of the helix for one turn.
Using rotate3d with the 2 point method, rotate the yellow line down by the angle theta about an axis defined by the green line. The result should look like this.
The yellow line will be used as a reference for editing a spline. Add a vertical line (cyan) at the bottom of the of the vertical line that passes through the center of the helix axis.
Create a spline with with 6 fit points as shown. The spline (white) should start at the end of the helix and end at the vertical red line.
Click the pulldown next to the spline and change to Control Vertices for editing.
Move the second CV from the helix end, and using osnap nearest, move it to the yellow line. This will ensure that the slope of the spline will be the same as the helix.
In the same manner move the next to the last CV to the cyan line.
We now have a spline with the appropriate slopes at the start and end. We now need to adjust the location of the other CVs.
Define a UCS with its x axis along the green line and its Y axis along the vertical red line
Use plan to view the XY plane.
With osnaps off and ortho mode active, move the CV's (but not the first two or last two) as shown.
Go to the right view and make the ucs active for that view
Move the CVs up or down (with ortho active) to yield a smooth shape that does not have a curvature reversal.
Edit the CVs as needed being careful the the active UCS is parallel to the view.
