the bow and stop of a standard EVVA 4KS key (SL)

Evva4KSBowAndStop.scad

// unit: 1mm

key_thickness = 2.26;
bow_width = 25.5;
bow_corner_radius = 6.0;
bow_corner_advance = 12.25;
bow_curve_advance = 10.0;
bow_curve_radius = 3.0;
bow_curve_outer_offset = 3.25;
stop_width = 13.0;
stop_advance = 5.517;
stop_tip_radius = 0.5;
ring_hole_radius = 3.25;
ring_hole_offset = 2.75;

$fn = $preview ? 8 : 32;

// code borrowed from nophead
// http://forum.openscad.org/Script-to-replicate-hull-and-minkoswki-for-CSG-export-import-into-FreeCAD-td16537.html#a16556
module rounded_polygon(points)
    difference() {
        len = len(points);
        union() {
            for (i = [0:len-1])
                if (points[i][2] > 0)
                    translate([points[i].x, points[i].y])
                        circle(points[i][2]);

            polygon([
                for (i = [0:len-1])
                    let (ends = tangent(points[i], points[(i + 1) % len]))
                        for (end = [0, 1])
                            ends[end]
            ]);
        };
        for (i = [0:len-1])
            if (points[i][2] < 0)
                translate([points[i].x, points[i].y])
                    circle(-points[i][2]);
     }
;

function tangent(p1, p2) =
    let (
        r1 = p1[2],
        r2 = p2[2],
        dx = p2.x - p1.x,
        dy = p2.y - p1.y,
        d = sqrt(dx*dx + dy*dy),
        theta = atan2(dy, dx) + acos((r1 - r2) / d),
        xa = p1.x + (cos(theta) * r1),
        ya = p1.y + (sin(theta) * r1),
        xb = p2.x + (cos(theta) * r2),
        yb = p2.y + (sin(theta) * r2)
    )
        [[xa, ya], [xb, yb]];
// end borrowed code

key_points = [
    [
        // bottom left corner
        0,
        0,
        bow_corner_radius
    ],
    [
        // left "midpoint"
        0,
        bow_corner_advance,
        bow_corner_radius
    ],
    [
        // middle of left curve circle
        bow_curve_outer_offset - bow_corner_radius,
        bow_corner_advance + bow_curve_advance,
        -bow_curve_radius
    ],
    [
        // left stop tip
        -bow_corner_radius + bow_width/2 - stop_width/2 + stop_tip_radius,
        bow_corner_advance + bow_curve_advance + stop_advance,
        stop_tip_radius
    ],
    [
        // right stop tip
        -bow_corner_radius + bow_width/2 + stop_width/2 - stop_tip_radius,
        bow_corner_advance + bow_curve_advance + stop_advance,
        stop_tip_radius
    ],
    [
        // middle of right curve circle
        bow_width - bow_corner_radius - bow_curve_outer_offset,
        bow_corner_advance + bow_curve_advance,
        -bow_curve_radius
    ],
    [
        // right "midpoint"
        bow_width - 2*bow_corner_radius,
        bow_corner_advance,
        bow_corner_radius
    ],
    [
        // bottom right corner
        bow_width - 2*bow_corner_radius,
        0,
        bow_corner_radius
    ],
];
difference()
{
    // bore keyhole
    linear_extrude(height=key_thickness)
        rounded_polygon(key_points);
    translate([
        -bow_corner_radius + bow_width/2,
        -bow_corner_radius + ring_hole_offset + ring_hole_radius,
        -5
    ])
        cylinder(
            r=ring_hole_radius,
            h=10
        );
};