Hi Gene,
You don't need to know the maths involved here,  there are functions
written to do all the maths and you need to just know how to use them.
Regards

On Tue, 25 Jul, 2023, 7:42 am gene heskett, gheskett@shentel.net wrote:

On Mon, Jul 24, 2023 at 11:36:35PM +0530, Sanjeev Prabhakar wrote:

Isn't fillet about the same as:

minkovski with a sphere of the fillet radius, Then invert, again
minkovski with that sphere and then invert again.

That would at least give a defined result for my "difficult case".

Roger. 

--
** 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.

I have not used minkowski method in openscad, maybe someone else can comment

On Tue, 25 Jul 2023 at 14:34, Rogier Wolff R.E.Wolff@bitwizard.nl wrote:

Three minkowskis of any non-trivial shape takes forever. This example takes
more than 5 minutes:

[image: round.png]

On Tue, 25 Jul 2023 at 15:56, Sanjeev Prabhakar sprabhakar2006@gmail.com
wrote:

On 25.07.23 17:18, nop head wrote:

What's the code for this example?

ciao,
Torsten.

It is the round_3D test from NopSCADLib. I have distilled it out to this:

$fa = 6;
$fs = 0.25;
inf = 1e10;      // very big
eps = 1/128;    // small fudge factor to stop CSG barfing on coincident
faces.
layer_height    = 0.25;
teardrop_angle  = 45;

function r2sides(r) = $fn ? $fn : ceil(max(min(360/ $fa, r * 2 * PI / $fs),
5));    //! Replicates the OpenSCAD logic to calculate the number of sides
from the radius
function r2sides4n(r) = floor((r2sides(r) + 3) / 4) * 4;
//! Round up the number of sides to a multiple of 4 to ensure
points land on all axes

module circle4n(r, d = undef) {                    //! Circle with
multiple of 4 vertices
R = is_undef(d) ? r : d / 2;
circle(R, $fn = r2sides4n(R));
}

module extrude_if(h, center = true)                //! Extrudes 2D object
to 3D when h is nonzero, otherwise leaves it 2D
if(h)
linear_extrude(h, center = center, convexity = 5) // 3D
children();
else
children();                                // 2D

module teardrop(h, r, center = true, truncate = true, chamfer = 0,
chamfer_both_ends = true, plus = false) { //! For making horizontal holes
that don't need support material, set truncate = false to make
traditional RepRap teardrops that don't even need bridging
module teardrop_2d(r, truncate) {
er = layer_height / 2 - eps;    // Extrusion edge radius
R = plus ? r + er : r;          // Corrected radius
offset = plus ? -er : 0;        // Offset inwards
hull()
for(side = [0 : 1])
mirror([side, 0, 0])
intersection() {
hull()
translate([offset, 0]) {
circle4n(R);

                            if (teardrop_angle > 0) {
                                x = R * tan(teardrop_angle / 2);
                                if(truncate)
                                    translate([0, R / 2])
                                        square([2 * x, R], center =

true);
else
polygon([[0, 0], [eps, 0], [0, R +
x * tan(min(teardrop_angle, 90 - eps))]]);
}
}
translate([0, -2 * R])
square([R, 4 * R]);
}
}

render(convexity = 5)
    extrude_if(h, center)
        teardrop_2d(r, truncate);

}

module offset_3D(r, chamfer_base = false) { //! Offset 3D shape by
specified radius r, positive or negative.
module ball(r)
if(chamfer_base)
rotate_extrude()
intersection() {
rotate(180)
teardrop(0, r);

                translate([0, -r])
                    square([r, 2 * r]);
            }
    else
        sphere(r);

if(r > 0)
    minkowski() {
        children();

        ball(r);
    }
else
    if(r < 0)
        render() difference() {
            cube(inf / 2, center = true);

            minkowski() {
                difference() {
                    cube(inf, center = true);

                    children();
                }
                ball(-r);
            }
        }
    else
        children();

}

module round_3D(r, ir = undef, or = undef, chamfer_base = false) { //!
Round a 3D child single radius or separate inside and outside radii
IR = is_undef(ir) ? r : ir;
OR = is_undef(or) ? r : or;
offset_3D(OR, chamfer_base)
offset_3D(-OR -IR, chamfer_base)
offset_3D(IR, chamfer_base)
children();
}

module shape()
difference() {
square(40, center = true);

    square([20, 20], center = true);
}

module rounds() {
translate([50, 0])
round_3D(or = 4, ir = 2, chamfer_base = true, $fn = 16)
linear_extrude(40, center = true)
shape();
}

rounds();

On Tue, 25 Jul 2023 at 16:37, Torsten Paul Torsten.Paul@gmx.de wrote:

here is another approach for filleting such type of intersection, it was
suggested by someone earlier, I did some modification and it is super
efficient.
it took 0.4 sec to render.
But it works only for convex intersections.
fillet here is 5 mm
[image: Screenshot 2023-07-26 at 6.33.44 AM.png]

On Tue, 25 Jul 2023 at 20:25, Sanjeev Prabhakar sprabhakar2006@gmail.com
wrote:

On Wed, 2023-07-26 at 06:35 +0530, Sanjeev Prabhakar wrote:

On my machine...

F5: Total rendering time: 0:00:00.789
F6: Total rendering time: 0:00:00.290

Ubuntu MATE,
OpenSCAD version 2023.02.15.ai13654