When you say you want a helix with a circular cross section, do you mean
measured in the usual way, normal to the helical path, or are you looking
at some other cross section?

What's wrong with

include<BOSL2/std.scad>
spiral_sweep(circle(r=2,$fn=32), h=20, r=10,turns=3);

On Fri, Oct 25, 2024 at 7:36 AM mike.fraser.1945+osc--- via Discuss <
discuss@lists.openscad.org> wrote:

On Fri, Oct 25, 2024 at 11:35:59AM +0000, mike.fraser.1945+osc--- via Discuss wrote:

Do you mean this?

r = 15;

d = 4;
l = 20;
nr = 4.5;
nsteps = 300;

$fs = .1;
$fa = 2;
module mys (n)
{
rotate (n * nr * 360/nsteps) translate ([d,0,n*l/nsteps]) sphere (d=d);
}

for (i=[0:1:nsteps-1])
hull () {mys (i);mys(i+1);}

--
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**    Delftechpark 11 2628 XJ  Delft, The Netherlands.  KVK: 27239233    **
f equals m times a. When your f is steady, and your m is going down
your a** is going up.  -- Chris Hadfield about flying up the space shuttle.
**  'a' for accelleration.

I have created a module called helix_extrude as part of my suite of
utility functions and modules:
https://gitlab.com/ktpanda/openscad-common

use <ktpanda/funcs.scad>
use <ktpanda/shapes.scad>

$fn = 80;
circle_rad = 3;
helix_rad = 20;
helix_rise = 8;

helix_extrude(points=circlepts(circle_rad), ofs=[helix_rad, 0],
cofs=[0, helix_rise], angle=360*10, convex=true);

points is a list of 2D points like you would pass to polygon
ofs is a base offset to apply to points
cofs is how much ofs should increase per turn.
angle defines the ending angle and encodes how many turns the helix has
convex is a hint that points defines a convex polygon

The ends will be circular, but the points will be sheared upward and
not normal to the helix. A circular cross section might require some
tweaking.

On Fri, Oct 25, 2024 at 7:07 AM Rogier Wolff via Discuss
discuss@lists.openscad.org wrote:

you get a helix by simply wrapping a wire around a cylinder ...

https://imgur.com/a/hmYALpM

🤣🤣

On Fri, Oct 25, 2024 at 4:46 PM Katie Rust via Discuss <
discuss@lists.openscad.org> wrote:

On 10/25/24 07:36, mike.fraser.1945+osc--- via Discuss wrote:

I am doing this in both linuxcnc and in openscad, by rendering each
"slice" of a buttress thread at a slight tilt angle, thereby blending
the resultant surface areas effectively at the thread angle. Actually
its rendered once, then rotated into place. Speeds rendering when the
spiral is 20 turns of the screw long in 2 start and the slice is a half
a degree thick. More than one way to skin that cat. ;o)>
Gene.

Cheers, Gene Heskett, CET.

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.

• Louis D. Brandeis

Let d be the diameter of the circle and alpha be the angle of the helix.
Then create a circle of diameter d, scale it by [1, 1/cos(90-alpha)], and
linear_extrude that. I think that’s what you want.

On Fri, Oct 25, 2024 at 11:43 AM gene heskett via Discuss <
discuss@lists.openscad.org> wrote:

I don't think that is quite right because if you slice a helix you don't
get an ellipse. It is an ellipse bent around the circle of the spiral.

On Fri, 25 Oct 2024 at 18:10, Father Horton via Discuss <
discuss@lists.openscad.org> wrote:

I think what he wants is what you’d get if you wrapped a wire with a
circular cross section around a cylinder. And I think that’s what this will
produce.

On Fri, Oct 25, 2024 at 12:28 PM nop head via Discuss <
discuss@lists.openscad.org> wrote:

If you are using sweep the profile is just a circle but if you are linear
extruding with a twist then the profile is what you would get if you slice
a spiral spring horizontally. That isn't an ellipse. An ellipse is what you
would get if you sliced an inclined cylinder but a helix bends so it's
cross section is an ellipse bent around the helix diameter.

On Fri, 25 Oct 2024, 19:12 Father Horton via Discuss, <
discuss@lists.openscad.org> wrote: