// Sheet-metal Z bracket (offset bracket), 2 mm aluminium
// Units mm, Z up, part resting on Z=0.
// Bottom flange extends -X, vertical web, top flange extends +X.

/* [Sheet] */
thickness = 2;          // [0.5:0.1:6]
bend_radius = 2;        // inside bend radius [0.5:0.1:10]
k_factor = 0.44;        // [0.2:0.01:0.5]

/* [Geometry] */
width = 30;             // [10:1:100]
offset_height = 20;     // outside-to-outside flange offset [8:0.5:100]
flange_length = 25;     // from outside of bend (outer mold line) [10:0.5:100]
hole_diameter = 4.5;    // [0:0.1:15]

/* [Output] */
mode = "folded";        // [folded, flat2d, flat3d]

/* [Hidden] */
$fn = 96;
T = thickness; R = bend_radius; K = k_factor;
ro = R + T;                                   // outer bend radius
flat_flange = flange_length - ro;             // straight part of each flange
flat_web = offset_height - 2 * ro;            // straight part of web
BA = (PI / 2) * (R + K * T);                  // bend allowance, 90 deg
flat_len = 2 * flat_flange + flat_web + 2 * BA;
hole_from_end = flange_length / 2;            // hole centred on nominal flange

assert(flat_web >= 0, "offset too small for bend radius");
assert(flat_flange > hole_diameter, "flange too short");

module sector(cx, cz, a0) {
    // annulus sector from angle a0 to a0+90 in XZ (angle measured from +X toward +Z)
    translate([cx, width, cz]) rotate([90, 0, 0])
        linear_extrude(width)
            intersection() {
                difference() { circle(r = ro); circle(r = R); }
                rotate(a0) square([ro + 1, ro + 1]);
            }
}

module hole_z(x) {
    translate([x, width / 2, -1]) cylinder(d = hole_diameter, h = offset_height + 2);
}

module folded() {
    // web outer face (bottom bend side) at x = T, inner at x = 0
    difference() {
        union() {
            // bottom flange: z in [0,T], x from T - flange_length to T - ro
            translate([T - flange_length, 0, 0]) cube([flat_flange, width, T]);
            // bottom bend: centre at (T - ro, ro) = (-R, ro)
            sector(-R, ro, 270);
            // web: x in [0,T], z from ro to offset_height - ro
            translate([0, 0, ro]) cube([T, width, flat_web]);
            // top bend: centre at (ro, offset_height - ro)
            sector(ro, offset_height - ro, 90);
            // top flange: z in [H-T, H], x from ro to flange_length
            translate([ro, 0, offset_height - T]) cube([flat_flange, width, T]);
        }
        hole_z(T - hole_from_end);
        hole_z(hole_from_end);
    }
}

module flat_outline() {
    difference() {
        square([flat_len, width]);
        translate([hole_from_end, width / 2]) circle(d = hole_diameter);
        translate([flat_len - hole_from_end, width / 2]) circle(d = hole_diameter);
    }
}

if (mode == "folded") folded();
else if (mode == "flat2d") flat_outline();
else linear_extrude(T) flat_outline();

echo(str("FLAT ", flat_len, " x ", width, "  BA=", BA));