One way to draw a 3D spiral with out a program is to use spline or the
polar coordinate point entry ( distance < angle, Z)
To make this easy you would do this off a User defined UCS origin
distance being the radius of the spiral
angle being the angle of incrimination about a circle.
Z being the rise per angular step.
for a simple example a spiral a 6 unit rad and 6 segments about a circle and
a 1 1/2 unit rise per rotation would enter as
6,0,0 ( start point)
then set the tangents
If you need to extrude something along a 3d spiral use the 3dpline as a path
the spline will not work.
The smaller the angle of segmentation the smoother it looks .
also if you extrude along the 3dpline the profile will rotate as it sweeps
along the 3dpline.
Terry is correct.
I have Some cad training using a book by John E. Wilson and the book says
the same thing.
To male it even easier go to www.freecadapps.com and search for 'spiral'
and there is a 3Dspiral program
I'm using AutoCAD 2002 in witch command 3Dpline does not exist, and
like You said, neither extrude nor tabsurf works with spline.
So it looks like the only way is lots of UCSistems, many arcs and
extrusions. Unless You have any other idea.
Sorry, just meant to say the command is "3dpoly" and not "3dpline", whether
or not it works for your application. I just found a link that may or may
not help you, but will give it to you anyway because I think it does the
best job describing how to model something that is fundamentally a 3d
spiral. It is an in-depth tutorial on modeling a 3d screw, but perhaps you
can apply the concepts to your stairway.
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