On 9/13/2022 3:14 PM, laich2@gmail.com wrote:

No, but a note:  you might think that linear_extrude with a twist is a
good way to generate helix-like shapes, but it really isn't.  The
problem is that you usually want to specify a cross-section across the
helix - nearly, but not precisely, a vertical cross-section, while what
you would have to supply with linear_extrude is a horizontal cross-section.

To get a helix with a round cross-section like this:

what you need to give to linear_extrude is a shape like this:

I'm sure that one of the mathematicians could tell you how to generate
that shape - I sure can't.  I generated it by using a sweep function to
create the helix, and then taking a cross section of the helix.

Here's that helix, using BOSL2's path_sweep module:

include <BOSL2/std.scad>
r = 20;
path_sweep(circle(5), [
    for (i=[0:10:900]) [ r*cos(i), r*sin(i), i/10 ]
]);

I have an old helical coil design on thingiverse which you can try:
https://www.thingiverse.com/thing:1098806

On Tue, Sep 13, 2022 at 8:12 PM Jordan Brown openscad@jordan.maileater.net
wrote:

If you're going to use BOSL2, then spiral_sweep() already exists for just this purpose:
include <BOSL2/std.scad>
spiral_sweep(circle(5), h=90, r=20, turns=2.5);

• Revar

here's some generic code for spirals/threads, whatever.

clw = true;  // direction of spiral
p = 15;      // pitch of spiral
n = 3.5;     // number of 'threads'
res = 100;   // number of 'steps' in circle
di = 20;     // diam of os of spiral
d = 5;       // diam of 'wire'

////////////////////

t = n*res;    //total number of steps
s = (res/360)*di/2; // width of profile
v = p/res;   // vertical shift per inc of rotation
//a = 360/res; // angle per step
a=clw==true ?  360/res  : -360/res;

module xsec(){
  $fn=80;
    translate([di-(d/2),0,0])
    rotate([90,0,0])
  //cylinder (d=d,h=s/2);  // whatever 'profile' you like
    cube([d,d,s/2],true);
}

for (i=[0:1:t]){
   translate([0,0,iv])
   rotate([0,0,ia])
   xsec();
 }

It's relatively simple to change the profile or resolution as required,
to make buttress threads, Whitworth profile, whatever. Easy enough to
convert to a function/module with relevant parameters, change
resolution, etc..

On 13/09/2022 23:14, laich2@gmail.com wrote: