In the end, that is exactly what I did, Nathan, but the idea in my head
was much simpler than the code that resulted.  And the "folds" are not
very pretty.  Functional, though.

On 11/23/2025 6:30 PM, Nathan Sokalski via Discuss wrote:

You probably want to also specify the bend radius and rotate_extrude a
curve at the fold line.

On Sun, 23 Nov 2025 at 23:36, Jon Bondy via Discuss <
discuss@lists.openscad.org> wrote:

I can do that for sure, but unfortunately only in python.
Regards

On Mon, 24 Nov, 2025, 1:52 am Jon Bondy via Discuss, <
discuss@lists.openscad.org> wrote:

On 11/23/2025 12:21 PM, Jon Bondy via Discuss wrote:

I think I could do it (intersecting with two appropriately-positioned
big cubes, and appropriately rotating the results of one).

However, before I figure out the answer... if you truly mean a 2D
object, you're getting into a weird area:  2D objects that are not on
the Z=0 plane.  OpenSCAD will do such operations, and will display
something sensible, but after that there isn't much that you can do with
them.  As 2D objects, you can only export them to 2D formats, which
won't be all that useful no matter what it does.  (And I think what it
will do is project back down to Z=0.)

So what are you really trying do to?  If you're just trying to visualize
the results, I can work it out for you.  If it's something more than
that, then we'd need to talk about the details.

Also note:  folding one 2D object is more or less straightforward. 
But folding it again is much less straightforward, as the big cubes
for subsequent folds start intersecting with unintended parts of the model.

Jordan:

Thanks for helping me think about this.

Once I sent the "2D" message, I realized that I really wanted to do it
with 3D objects, but thin ones.  Conceptually 2D, but actually 3D.

This is what I came up with to make the fold.  Crude and ugly, but my
customer needs glasses, so all is good.

I can imagine a general library to do things like this, but I am sure
that there are people on this list who are more sophisticated than I am

eps = 0.01;
slop = 0.2;
$fa = 3;
$fs = 0.2;
inches = 25.4;

// ball diameters
bd25 = 25.3 + slop;
an   = 27;                // angle from vertical to surface of bowl

ct  = 4;        // circle thickness
cd  = 130 - 6;    // circle diameter
cr  = cd/2;        // circle radius
cwa = 52;        // fold angle for circle wings
ca  = 67;        // angle between the wings
ca2 = ca/2;        // half angle between wings

module Circle(d2Fac)
    // d2Fac is 1 for regular cylinder, 0.8 for sharp edges for the wings
    cylinder(h = ct, d1 = cd, d2 = d2Fac*cd);

module Vee() {
    // the vee
    difference() {
        // the circle
        translate([0, cr, 0])
            Circle(1);
        // trim off where the wings will be
        translate([0, 0, -eps])
            rotate([0, 0, -ca2])
                cube([200, 200, ct + 2eps]);
        translate([0, 0, -eps])
            rotate([0, 0, 90 + ca2])
                cube([200, 200, ct + 2eps]);
        }
    // flap
    // rotated back into place
    rotate([0, 0, -ca2])
    // rotated up in the air
    rotate([0, -cwa, 0])
    // rotated so fold is along Y axis
    rotate([0, 0, ca2])
    // the flap
    intersection() {
        translate([0, cr, 0])
            Circle(0.8);
        translate([0, 0, -eps])
            rotate([0, 0, -ca2])
                cube([200, 200, ct + 2*eps]);
        }
    }
Vee();

On 11/25/2025 1:38 PM, Jordan Brown wrote:

Note that you can tidy your code a bit (at least I think it's tidier) by
writing apply(rot(from=r, to=UP)*move(-c), path) for example.  You also
don't have to use apply as all the transformations can also directly
operate on a path.  Setting orient is basically the same as rot(from=UP,
to=orient_direction).  But spin gets wonky because Revar made it spin
around the anchor point, not the object center.  This seems wrong to me.

Also I don't think Jordan was saying that 2d objects in 3 dimensions are
fundamentally useless.  Rather he meant specifically that OpenSCAD 2d
geometry is not useful if it's not on the XY plane.  You used a point list
to work around this limitation.

On Tue, Nov 25, 2025 at 4:55 PM Bob Carlson via Discuss <
discuss@lists.openscad.org> wrote:

On 11/25/2025 2:06 PM, Adrian Mariano via Discuss wrote:

Yes.

And note that that particular "won't be all that useful" comment was
with respect to exporting a non-XY-plane 2D object to a 2D format. 
Doubly so as here) when we were potentially talking about multiple 2D
objects on different planes.

rotate([0,30,0]) translate([-10,0,0]) square(10);
rotate([0,-30,0]) square(10);

It's hard to see how exporting that to a 2D format (other than, as here,
an image) would be useful.  (OK, very limited cases like making plan and
elevation views.)