// ============================================================
//  Elbow Inlet Adapter
//  40 OD vertical stub -> smooth 90 deg bend -> 70 mm run
//
//  Bore profile (per spec):
//    * 35 mm ID through the vertical leg and the whole elbow
//    * necks 35 -> 30 mm over the first 10 mm of the run (venturi)
//    * widens 30 -> 32.1 mm over the remaining 60 mm (opening)
//  Outer profile:
//    * 40 mm OD through leg + elbow, then a single gradual taper
//      down to the opening OD; wall never below `tip_wall`.
//
//  The bend is a swept quarter-torus (not a mitred joint), which
//  is kinder to both airflow and layer adhesion.
// ============================================================

/* [Vertical inlet leg] */
// Outer diameter of the vertical stub and elbow
inlet_od = 40;
// Inner diameter through the leg and elbow
inlet_id = 35;
// Straight rise before the bend starts ("goes up a few mm")
leg_h = 5;

/* [Elbow] */
// Centerline bend radius. Must be > inlet_od / 2 (else the torus
// self-intersects). Bigger = gentler sweep but taller part.
bend_r = 24;

/* [Horizontal run] */
// Length of the straight run after the bend
run_len = 70;
// The bore necks from inlet_id down to throat_id over this length
throat_len = 10;
// Narrowest bore diameter
throat_id = 30;
// Bore diameter at the opening (sized to accept your mating part)
tip_id = 32.1;
// Wall thickness at the opening
tip_wall = 2.5;

/* [Quality] */
$fa = 1.5;
$fs = 0.4;

// ---------------- derived ----------------
tip_od = tip_id + 2 * tip_wall;          // 37.1 at defaults
elbow_exit = [bend_r, 0, leg_h + bend_r]; // where the run begins
eps = 0.01;

// quarter-torus sweep: starts at [0,0,leg_h] pointing +Z,
// exits at elbow_exit pointing +X. Pass a 2D child (circle) to sweep.
module elbow_sweep() {
    translate([bend_r, 0, leg_h])
        mirror([1, 0, 0])
            rotate([90, 0, 0])
                rotate_extrude(angle = 90)
                    translate([bend_r, 0])
                        children();
}

// everything solid (no bore)
module solid() {
    cylinder(h = leg_h + eps, d = inlet_od);                 // leg
    elbow_sweep() circle(d = inlet_od);                      // bend
    translate(elbow_exit)                                    // run
        rotate([0, 90, 0])
            cylinder(h = run_len, d1 = inlet_od, d2 = tip_od);
}

// the complete air path, slightly over-extended at both open ends
module bore() {
    translate([0, 0, -1]) cylinder(h = leg_h + 1 + eps, d = inlet_id);
    elbow_sweep() circle(d = inlet_id);
    translate(elbow_exit) rotate([0, 90, 0]) {
        // venturi neck: 35 -> 30 over throat_len
        translate([0, 0, -eps])
            cylinder(h = throat_len + 2*eps, d1 = inlet_id, d2 = throat_id);
        // gradual widening: 30 -> 32.1 over the rest, punched past the tip
        widen = run_len - throat_len;
        slope = (tip_id - throat_id) / widen;
        translate([0, 0, throat_len])
            cylinder(h = widen + 1, d1 = throat_id, d2 = tip_id + slope * 1);
    }
}

module adapter() {
    difference() {
        solid();
        bore();
    }
}
adapter();

// Printing: stand it on the big opening face (run vertical, leg
// curving over at the top). The sweep keeps overhangs gradual;
// a little tree support under the leg stub is all it needs.