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);}

--
** R.E.Wolff@BitWizard.nl ** https://www.BitWizard.nl/ ** +31-15-2049110 **
**    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:

Jordan posted a detailed description of the banana shaped cross section you
need to make a helix with linear extrude and twist. Definitely not a circle
or an ellipse.

On Fri, Oct 25, 2024 at 14:44 nop head via Discuss <
discuss@lists.openscad.org> wrote:

On 10/25/2024 11:54 AM, Adrian Mariano via Discuss wrote:

https://lists.openscad.org/empathy/thread/DC2WDIIZS57SIDWVAVKDN3NEN4MOZOYM

Hans did the same thing much earlier in a Thingiverse post.

Attached image

I realize I am late to the party, but here is what I sometimes do when I
need to create some sort of helical feature. Any convex 2D geometry (in
this case a circle) can be passed as a child to the helix module and it
stitches together a number of thin slices of the profile via calls to
hull():

// extrude a helix with radius 'Radius', N revolutions, pitch
module helix (Radius, N, pitch, fa=10, eps=1e-3) {
for (i=[0:N360/fa-1]) {
hull() {
rotate([0, 0, ifa])
translate([Radius, 0, pitchifa/360])
rotate([90+180*(pitch/(23.14Radius))/3.14, 0, 0])
linear_extrude(height=eps, center=true) children();
rotate([0, 0, (i+1)fa])
translate([Radius, 0, pitch(i+1)fa/360])
rotate([90+180(pitch/(23.14Radius))/3.14, 0, 0])
linear_extrude(height=eps, center=true)
children();
}
}
}

helix(Radius=4, N=4, pitch=3, fa=5) circle(r=1, $fn=30);

On Fri, Oct 25, 2024 at 3:20 PM Jordan Brown via Discuss <
discuss@lists.openscad.org> wrote:

On 25/10/2024 12:35, mike.fraser.1945+osc--- via Discuss wrote:

see my post of the 14th (and 19th). Just use a circular profile. Or use
cadstudio.

cadstudio = cadview...

On 25/10/2024 21:35, Raymond West via Discuss wrote:

These are all made by sweeping a circle on a helical path. Much easier than
using linear_extrude with a  twist.

[image: image.png]

On Fri, 25 Oct 2024 at 22:40, Raymond West via Discuss <
discuss@lists.openscad.org> wrote:

Original poster is sitting quite. It seems he has got his answer

On Sat, 26 Oct, 2024, 3:18 am nop head via Discuss, <
discuss@lists.openscad.org> wrote:

all I need is a design for a nut 😉

On 25/10/2024 22:48, nop head via Discuss wrote:

nice one

On Sat, 26 Oct 2024 at 16:44, Raymond West via Discuss <
discuss@lists.openscad.org> wrote:

Maybe like the screws that can be tightened turning both left and right?

https://www.youtube.com/watch?app=desktop&v=_48-Ike_i6M

That can hurt your noggin, but I get it...

EBo --

On Sat, Oct 26, 2024 at 8:33 AM Sanjeev Prabhakar via Discuss <
discuss@lists.openscad.org> wrote:

fwiw, I made a short length of threaded rod, about a month or two ago, 
with left and right hand threads, and matching huts, one lh thread,
t'other rh. (also an attempt at a nut that 'would go both ways). I
showed it to someone I know, but he liked it so much, he put it in his
pocket. This one will be toroidal, too big for a pocket. With sufficient
stiction between the nuts and the rod, if you hold one nut you think you
can tighten the other one against it, but you can't.

On 26/10/2024 18:56, John David via Discuss wrote:

Why wouldn't you be able to tighten one nut against another on the helical
threaded rod?  It does seem like the nuts would need to have their
threading skewed by the helical curve and angle.

For anyone who wants a simple example of the double threaded screw, there's
one here:

https://github.com/BelfrySCAD/BOSL2/wiki/threading.scad#module-threaded_rod

See Example 7.

On Sun, Oct 27, 2024 at 6:51 AM Raymond West via Discuss <
discuss@lists.openscad.org> wrote:

Hi Adrian,

if you hold one nut, the stiction can hold the stud, allowing the second
nut to be tightened against the first, but when the second nut touches
the first nut, the stud starts turning in the same direction as the
second nut, thus it can not tighten against the first nut. I've not got
my original, since a friend 'borrowed' it, so that is the best
explanation that I can remember. If you hold the stud, then you can
tighten both nuts together, but swap them over, and turn each in the
same direction, they move apart, of course.

I'm not sure of any practical application, but there are plenty of
double threaded nuts and bolts, but with the threads going in the same
direction. Many occurred when going from imperial to metric threads in
the UK🙁.

Best wishes,

Ray

On 28/10/2024 21:28, Adrian Mariano via Discuss wrote:

Ray, I think you're talking about the double threaded rod and I
misinterpreted you and thought you were referring to the threaded helix
that you posted.  I have printed the double threaded rod (from the above
posted BOSL2 example) and am still in possession of the print, so I know
how that thing behaves.

On Tue, Oct 29, 2024 at 4:14 PM Raymond West via Discuss <
discuss@lists.openscad.org> wrote:

On 6/25/25 13:04, Robbie Sandberg via Discuss wrote:

That is a limitation I don't have, but what I do in such a case is make
the threaded rod I'm using for a difference, enough longer that both
ends project beyond the length of the item its being differenced out of.
Unfortunately I don't see the code for "threaded_rod()" so I can't test
it  Can that be posted?l

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

As the subject says, it's a BOSL2 question, which is where threaded_rod is
to be found.

The cylinder() module by default places the cylinder with its bottom on the
XY plane.  You can use center=true to make it center. The BOSL2 commands by
default center objects, so the threaded rod will be centered.  It may work
better to combine this with cyl() which automatically centers for
consistent behavior.  Note that you probably want internal=true if you're
making a threaded hole.  Your model has a 50 unit tall cylinder, so its
top is at z=50.  The top of the threaded rod, which has height 16, is at
z=8.  Since you are beveling you will not want to follow Gene's advice to
make it oversized.  You have a  but your threaded rod is only 16 units
tall.  So you need to raise it by 50-8 units.  So like this:

difference() {
cylinder(h=50, d=16, $fn=150);
translate([0,0,1.5])
cylinder(h=32.5, d=12);
up(50-8)
threaded_rod(d=12, l=16, pitch=2, internal=true, bevel2=0.5, bevel1=0);
}

I took the bevel off the bottom because that works better.  Note that
internal=true causes the bevels to reverse.  And you may want to go up by
slightly more to ensure no issues with coplanar faces, but in this case I
think it only matters in preview, which doesn't affect you.  By slightly
more I mean 0.01 units.

The easier way to address this is with attachments.  That looks like this:

include<BOSL2/std.scad>
include<BOSL2/threading.scad>

diff()
cyl(h=50,d=16, $fn=150){
up(1.5)attach(BOT,BOT,inside=true) cyl(h=32.5,d=12);
attach(TOP,TOP,inside=true)
threaded_rod(d=12, l=16, pitch=2, internal=true, bevel2=0.5,
bevel1=0);
}

You can also in general explicitly anchor BOSL2 objects so you know where
they are, e.g. with anchor=BOTTOM to put the bottom at the origin, or
anchor=CENTER to center it at the origin.

On Wed, Jun 25, 2025 at 2:15 PM gene heskett via Discuss <
discuss@lists.openscad.org> wrote:

On 6/25/25 16:39, Adrian Mariano via Discuss wrote:

Unfortunately I can't make it work by adding

include </home/gene/.local/share/OpenSCAD/libraries/BOSL2/std.scad>

include
</home/gene/.local/share/OpenSCAD/libraries/BOSL2/threading.scad; as
lines 3 & 4..

Perhaps someone else can help this gentleman. Obviously Adrian, I need
to get more familiar with BOSL2, and/or I need to dl a newer version.

It is now complaining about an error in shapes3d.scad line 15. But it
won't copy/paste from the error box. URL for latest?

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

The example I posted does not require a recent copy of BOSL2, so your
issues may depend on installation issues, but you didn't post the error
messages so that makes a more detailed diagnosis impossible. You should be
able to include BOSL2 without needing the full path if you have your
library path set up correctly.

If you want the most recent BOSL2 it can be found at:

https://github.com/BelfrySCAD/BOSL2

On Wed, Jun 25, 2025 at 8:40 PM gene heskett via Discuss <
discuss@lists.openscad.org> wrote:

On 6/25/25 21:07, Adrian Mariano via Discuss wrote:

Apparently I don't.  And its not well covered in the cheat sheet.

Thank you.

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