new design: parameterized box with clip in lid
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// =====================================================================
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// Parametric box with clip-in lid
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// =====================================================================
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// PRINT NOTES
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// * Box: print open side UP. Lid: print flat (either face down).
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// * No supports needed - every overhang is <= 45 degrees.
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// * The snap beams flex in the XY plane, i.e. along the layer lines,
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// so they are strong (no bending across weak layer bonds).
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// * Suggested: 0.4 mm nozzle, 0.2 mm layers, 3+ perimeters, PLA/PETG.
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// Walls and beams are multiples of 0.4 mm -> full-width extrusions.
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// * Lid too tight? raise `clearance` (0.1 steps).
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// * Lid rattles? raise `snap_preload` (up to ~= clearance).
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// * Lid pops off too easily? raise `snap_depth` (0.1 steps) or `flex_t`.
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// =====================================================================
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/* [Box size - outer dimensions in mm] */
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length = 50; // X
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width = 50; // Y
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height = 30; // Z
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/* [Walls] */
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wall = 2.4; // side wall thickness
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floor_t = 1.6; // floor thickness
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corner_r = 3; // rounded vertical edges (0 = sharp)
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foot_chamfer = 0.4; // bottom edge chamfer, compensates "elephant foot" (0 = off)
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/* [Lid] */
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lid_t = 3; // lid thickness
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ledge = 0.8; // width of the shelf the lid rests on
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clearance = 0.2; // gap between lid and box
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/* [Snap fit] */
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snap_depth = 0.5; // how far the ridge sticks out
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snap_flat = 0.6; // flat tip of the ridge
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snap_preload = 0.15; // 0 = loose, for snug fit
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clip_count = 1; // clips per long edge
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clip_len = 30; // length of each flexible beam
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flex_t = 1.6; // beam thickness (thinner = softer clip)
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slot_w = 1.2; // slot width = room for the beam to flex
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/* [Options] */
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pry_notch = true; // small notch to get a fingernail under the lid
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notch_r = 5;
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part = "print"; // [print, box, lid, assembly]
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cutaway = false;
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$fn = 48;
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// ---------------------------------------------------------------------
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// Derived values
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// ---------------------------------------------------------------------
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R = corner_r;
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rim_wall = wall - ledge; // wall thickness in the lid rebate
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rr = max(R - rim_wall, 0); // rebate corner radius
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rl = length - 2*rim_wall; // rebate size
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rw = width - 2*rim_wall;
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lid_l = rl - 2*clearance; // lid size
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lid_w = rw - 2*clearance;
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lid_r = max(rr - clearance, 0);
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// The clips go on the two long edges of the lid.
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long_x = length >= width;
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edge_l = long_x ? lid_l : lid_w; // length of the clip edges
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edge_w = long_x ? lid_w : lid_l; // lid size across the clip edges
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hb = snap_depth + snap_flat/2; // half-height of ridge at its base
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avail = edge_l - 2*lid_r - 4; // straight edge usable for clips
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seg = avail / clip_count;
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clip_l = min(clip_len, seg - 4);
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ridge_l = clip_l - slot_w;
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clip_x = [for (i = [0 : clip_count-1]) -avail/2 + seg*(i + 0.5)];
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assert(corner_r >= 0 && corner_r <= min(length, width)/2 - 0.1,
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"corner_r is too large for this box");
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assert(height >= floor_t + lid_t + 8,
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"height is too small for floor + lid");
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assert(rim_wall - snap_depth >= 0.8,
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"Rim wall too thin at the groove: reduce ledge/snap_depth or increase wall");
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assert(lid_t/2 - snap_preload - hb >= 0.2,
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"Lid too thin for the snap ridge: increase lid_t or reduce snap_depth/snap_flat");
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assert(edge_w/2 - flex_t - slot_w >= 3,
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"Box too narrow for the flex slots: reduce flex_t/slot_w");
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assert(clip_count >= 1 && clip_l >= 8,
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"Box too short for this many clips: reduce clip_count");
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// ---------------------------------------------------------------------
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// Helpers
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// ---------------------------------------------------------------------
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module rrect(l, w, r) { // centred rounded rectangle (2D)
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if (r > 0.01) offset(r = r) square([l - 2*r, w - 2*r], center = true);
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else square([l, w], center = true);
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}
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// ---------------------------------------------------------------------
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// BOX
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// ---------------------------------------------------------------------
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module outer_shell() {
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if (foot_chamfer > 0)
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hull() {
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linear_extrude(0.01)
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rrect(length - 2*foot_chamfer, width - 2*foot_chamfer,
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max(R - foot_chamfer, 0));
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translate([0, 0, foot_chamfer])
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linear_extrude(height - foot_chamfer) rrect(length, width, R);
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}
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else
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linear_extrude(height) rrect(length, width, R);
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}
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// Snap groove running around the rebate wall.
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// Trapezoid profile with 45 degree flanks -> prints without supports.
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module snap_groove() {
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zc = height - lid_t/2 - snap_preload;
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ht = snap_flat/2;
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hull() {
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translate([0, 0, zc - ht]) linear_extrude(2*ht)
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rrect(rl + 2*snap_depth, rw + 2*snap_depth, rr + snap_depth);
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translate([0, 0, zc - hb]) linear_extrude(2*hb)
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rrect(rl, rw, rr);
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}
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}
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module pry_notch() {
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p = long_x ? [length/2, 0] : [0, width/2]; // on a short wall
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translate([p[0], p[1], height - lid_t - 1])
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cylinder(r = notch_r, h = lid_t + 2);
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}
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module box() {
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difference() {
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outer_shell();
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// main cavity
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translate([0, 0, floor_t]) linear_extrude(height)
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rrect(length - 2*wall, width - 2*wall, max(R - wall, 0));
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// rebate for the lid (leaves a ledge of width `ledge`)
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translate([0, 0, height - lid_t]) linear_extrude(lid_t + 1)
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rrect(rl, rw, rr);
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snap_groove();
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if (pry_notch) pry_notch();
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}
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}
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// ---------------------------------------------------------------------
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// LID
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// ---------------------------------------------------------------------
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// Ridge along +Y edge, centred on x = 0, z = 0. 45 degree flanks.
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module ridge(len) {
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e = 0.05;
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ht = snap_flat/2;
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rotate([90, 0, 90]) translate([0, 0, -len/2]) linear_extrude(len)
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polygon([[-e, -hb - e], [snap_depth, -ht],
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[snap_depth, ht], [-e, hb + e]]);
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}
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// Rounded slot
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module slot(len) {
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hull() for (x = [-1, 1])
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translate([x*(len - slot_w)/2, 0, 0]) cylinder(d = slot_w, h = lid_t + 2);
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}
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module lid_core(L, W) {
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difference() {
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union() {
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linear_extrude(lid_t) rrect(L, W, lid_r);
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for (s = [-1, 1]) scale([1, s, 1])
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for (cx = clip_x)
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translate([cx, W/2, lid_t/2]) ridge(ridge_l);
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}
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for (s = [-1, 1]) scale([1, s, 1])
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for (cx = clip_x)
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translate([cx, W/2 - flex_t - slot_w/2, -1]) slot(clip_l);
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}
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}
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module lid() {
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rotate([0, 0, long_x ? 0 : 90]) lid_core(edge_l, edge_w);
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}
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// ---------------------------------------------------------------------
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// OUTPUT
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// ---------------------------------------------------------------------
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module assembly() {
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big = 10 * max(length, width, height);
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difference() {
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union() {
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box();
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color("orange") translate([0, 0, height - lid_t]) lid();
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}
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if (cutaway) translate([-big/2, 0, -1]) cube([big, big, big]);
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}
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}
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if (part == "box") box();
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else if (part == "lid") lid();
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else if (part == "assembly") assembly();
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else { // "print": both parts side by side
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lid_ext_y = long_x ? lid_w : lid_l;
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box();
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translate([0, (width + lid_ext_y)/2 + 10, 0]) lid();
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}
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