# 3D spiral- how to make?

Hi everyone.
How can I make a 3D spiral? I need it for the balustrade of a 3D spiral stairway, so it must be "round". I hope you understand what I
mean.
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Bill
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That's no fun!

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One way to draw a 3D spiral with out a program is to use spline or the 3dpline and 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
spline 6,0,0 ( start point) 6<60,.25 6<120,.5 6<180,.75 6<240,1 6<300,1.25 6<360, 1.5 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.

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And if that looks too much like hard work use Excel to calculate each point and save the results as a script file.
Terry

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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

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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.

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"3dpoly"

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On Wed, 16 Jun 2004 12:11:36 -0500, "Larry Travis"

Yes, but I can't force it to go through the points when spline curve is used (in pedit).
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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.
Good luck, LT
wrote:

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