Stackable Mini-ITX NAS case

// Stackable Mini-ITX NAS case for a small printer (180 mm bed).
// A base module carries the board, bay modules carry drive trays on a bolt grid,
// and a fan lid closes the stack and pulls air up through it. Modules print
// upright as one piece, the lid prints upside down, the shield, trays and feet flat.
// Modules bolt together with M3 screws into nuts trapped in corner bosses.

/* [Parts] */
// The whole stack, or one part in print orientation. board_gauge is a thin frame with
// the four standoff holes: lay the board on it before printing the board module.
part = "assembly"; // [assembly, board_module, bay_module, tray_35, tray_35_hanging, lid, rear_shield, foot, board_gauge]
// Print a coupon set instead: the rear left corner of the board module and of a bay
// module, the matching strip of rear shield and one foot. Stack them, drop a nut in,
// bolt through, slide the shield in: every fit is tested in about an hour.
test_print = false;
// Size of the corner the coupons are cut from.
test_size = 40; // [30:2:60]
// Bay modules shown in the assembly.
bay_modules = 2; // [0:1:4]
// Show a drive hanging under the lowest bay, above the board.
hang_hdd = true;
// Pull the stack apart in the assembly view.
explode = 0; // [0:5:80]
// Show the board and the drives as ghosts in the assembly.
show_hardware = true;

/* [Board] */
// Board size, 170 for Mini-ITX.
board = 170; // [120:1:172]
// Gap between the board edge and the wall, each side.
board_clear = 0.5; // [0.3:0.1:1.5]
// Height of the printed standoffs under the board.
standoff_h = 6.5; // [4:0.5:10]
// Screw hole in the standoffs, 2.6 for a self tapping M3.
standoff_hole = 2.6; // [2.4:0.1:4.5]
// The four standoffs, each on its own: x from the left edge of the board seen from
// the front, y from the rear (I/O) edge. These NAS boards do not follow the Mini-ITX
// pattern, so measure all four with calipers and check them with board_gauge.
hole1_x = 6.35; // [2:0.05:168]
hole1_y = 10.16; // [2:0.05:168]
hole2_x = 163.5; // [2:0.05:168]
hole2_y = 23; // [2:0.05:168]
hole3_x = 6.35; // [2:0.05:168]
hole3_y = 163.65; // [2:0.05:168]
hole4_x = 163.65; // [2:0.05:168]
hole4_y = 163.65; // [2:0.05:168]
// Height of the board module. With a hanging drive the cooler gets board_h minus 44 mm.
board_h = 60; // [40:1:90]

/* [Front, rear and sides] */
// Extra depth in front of the board for the pico PSU that overhangs the front edge.
// Every millimetre adds to the 177 mm footprint; an A1 mini bed stops at 180.
front_clear = 2; // [0:0.5:10]
// Thin the front wall to 1.2 mm over the PSU, between psu_x0 and psu_x1 from the left.
front_relief = true;
psu_x0 = 0; // [0:1:160]
psu_x1 = 65; // [10:1:170]
// Thread diameter of the power button, 16 for the common vandal switch. 0 for none.
button_d = 16; // [0:0.5:22]
// Button position from the left, and height from the module bottom. 88 is centred.
button_x = 88; // [10:0.5:167]
button_z = 36; // [15:1:80]
// Shallow ring recessed around the button.
button_ring = true;
// Panel mount DC jack hole, 0 for none.
jack_d = 12; // [0:0.5:16]
// Where the DC jack sits: in the rear shield above the ports, or in a side wall.
jack_pos = "rear"; // [rear, right, left]
// Jack position: from the left edge of the board (rear), or from the rear (sides).
jack_x = 150; // [10:1:160]
// Jack height from the module bottom.
jack_z = 42; // [12:1:80]
// Intake band low on each side of every module.
vents = true;
// Horizontal dashes in rows, or short vertical slots.
vent_style = "horizontal"; // [horizontal, vertical]
// Width of the band along the side, centred.
vent_span = 96; // [30:2:150]
// Bottom of the band above the module bottom.
vent_z = 8; // [6:1:20]
// Slot width (vertical) or slot height (horizontal).
vent_w = 1.6; // [1.2:0.2:4]
// Horizontal: rows of dashes and dash length.
vent_rows = 3; // [1:1:6]
vent_dash = 20; // [8:1:40]
// Vertical: slot height and pitch.
vent_h = 12; // [6:1:30]
vent_pitch = 6; // [4:0.5:12]

/* [Drives] */
// Size of the disk, 3.5" by default.
hdd_w = 101.6; // [69:0.1:102]
hdd_l = 147; // [100:0.1:150]
hdd_h = 26.1; // [7:0.1:30]
// Room above the disk.
hdd_gap = 3; // [2:0.5:10]
// Height of the bolt grid bosses on the bay floor.
grid_boss_h = 3; // [2:0.5:5]
// Thickness of the drive tray.
tray_t = 3; // [2.5:0.1:4]
// Grid column the tray sits in (18 mm steps from the left): on the bay floor, and hanging under it.
tray_col = 1; // [0:1:2]
hang_col = 2; // [0:1:2]

/* [Lid] */
// Fan in the lid, 0 for a plain lid.
fan_size = 80; // [0, 40, 60, 80, 92, 120]
// Thickness of the fan.
fan_t = 25; // [10:1:30]
// Free air under the fan, so it can breathe over a drive.
fan_gap = 8; // [2:1:15]
// Relief pattern over the whole lid; it opens up over the fan.
lid_pattern = "ripple"; // [ripple, hex, diagonal]
// Depth of the relief. 0 for a flat lid.
lid_relief = 1; // [0:0.2:1.5]
// Chamfer on the top edge of the lid.
lid_ch = 2.5; // [0:0.5:4]

/* [Rear shield] */
// One opening in the rear shield: from the left edge of the board, its width, and its height from the shield bottom.
io_x = 0; // [0:0.5:170]
io_w = 170; // [10:0.5:170]
io_h = 20; // [5:0.5:60]

/* [Case] */
wall = 3; // [2.5:0.1:4]
floor_t = 2.5; // [2:0.1:4]
top_t = 2.5; // [2:0.1:4]
// Rounding of the vertical outer corners.
corner_r = 2; // [0:0.5:3]
// Chamfer on the top outer edge of every module, the seam line in the stack.
edge_ch = 0.8; // [0:0.1:1.5]
// Height and thickness of the stacking lip, and its play in the pocket.
lip_h = 4; // [3:0.5:6]
lip_t = 1.5; // [1.2:0.1:2]
lip_c = 0.2; // [0.1:0.05:0.4]
// M3 nut across flats, plus play.
nut_af = 5.7; // [5.4:0.1:6.2]
// Height of the screw-on feet.
foot_h = 8; // [5:0.5:15]

/* [Colour] */
// Display only, the STL carries no colour.
color_case = "Silver"; // [Silver, Gainsboro, White, DimGray, Black, SlateGray, FireBrick, SteelBlue, ForestGreen, Goldenrod]

/* [Hidden] */
$fn = 48;
pcb_t = 1.6;
S = board + 2 * (board_clear + wall);      // width
Sy = S + front_clear;                        // depth
holes = [[hole1_x, hole1_y], [hole2_x, hole2_y], [hole3_x, hole3_y], [hole4_x, hole4_y]];
skirt_t = wall - lip_t - lip_c;
rib_in = wall + lip_c + 0.1;
rib_t = 1.6;
grid_p = 18;
stop_len = 6;
stop_end = wall + stop_len;
groove_d = 1.0;
shield_t = 1.6;
bs = 9;                     // corner boss size
boss_h = 12;
nut_h = 2.8;
nut_ac = nut_af / cos(30);  // across corners
nut_top = 2.5;              // material above a trapped nut
bolt_d = 3.4;
bc = wall + bs / 2;         // bolt centre from the outer faces
z0 = lip_h + floor_t;
board_z = z0 + standoff_h;
rear_top = board_z - 0.5;
cell_in = rib_in + rib_t;   // corner cell starts here
plug = grid_p - rib_t / 2 - cell_in - 0.6;
bay_h = z0 + grid_boss_h + tray_t + hdd_h + hdd_gap;
lid_wall = rib_in + rib_t;
fan_boss_h = 3;
lid_h = top_t + (fan_size > 0 ? fan_boss_h + fan_t + fan_gap : 5);
fan_hole = lookup(fan_size, [[40, 32], [60, 50], [80, 71.5], [92, 82.5], [120, 105]]);
hex_af = 6;                 // honeycomb cell across flats
hex_w = 1.8;                // honeycomb wall
rip_p = 6;                  // ripple pitch
rip_w = 2.5;                // ripple groove width
dia_p = 8;                  // diagonal pitch
dia_w = 2;                  // diagonal groove width
vent_gap = 4;               // between dashes
vent_rp = vent_w + 2.4;     // row pitch
tray_span = ceil((hdd_w + 8) / grid_p) * grid_p;   // flange hole spacing, a grid multiple
tray_fx = (hdd_w - tray_span) / 2;                  // flange hole x, left of the drive edge
tray_l = 140;
tray_x = grid_p * tray_col + 9 - tray_fx;           // drive left edge in the bay
hang_x = grid_p * hang_col + 9 - tray_fx;           // same for the hanging drive
tray_y = grid_p;                                    // drive rear edge in the bay
hang_pad = lip_h + 0.3;                             // pads reach past the ribs to the floor
foot_s = 18;                                        // foot pad size
relief_t = 1.2;                                     // front wall left over the PSU

// ---- 2D outlines ----

module outer2d() {
  offset(r = corner_r) offset(delta = -corner_r) square([S, Sy]);
}

module inset2d(k) {
  offset(r = -k) outer2d();
}

module ring2d(a, b) {
  difference() { inset2d(a); inset2d(b); }
}

module annulus2d(r1, r2) {
  difference() { circle(r = r2); circle(r = r1); }
}

// Rib grid under the floor.
module ribs2d() {
  for (p = [grid_p : grid_p : S - grid_p / 2]) translate([p - rib_t / 2, 0]) square([rib_t, Sy]);
  for (p = [grid_p : grid_p : Sy - grid_p / 2]) translate([0, p - rib_t / 2]) square([S, rib_t]);
}

// Blocks in the rear corners of the pocket: they stop the stack sliding rearward.
module stops2d() {
  for (m = [0, 1]) translate([m ? S : 0, 0]) mirror([m, 0])
    translate([skirt_t - 0.05, skirt_t - 0.05]) {
      square([rib_in - skirt_t + 0.6, stop_end - skirt_t + 0.05]);
      square([stop_end - skirt_t + 0.05, rib_in - skirt_t + 0.6]);
    }
}

// Lip ring on top of a module, kept clear of the corners.
module lip2d(wt) {
  difference() {
    ring2d(wt - lip_t, wt);
    for (m = [0, 1], n = [0, 1]) translate([m ? S : 0, n ? Sy : 0]) mirror([m, 0]) mirror([0, n])
      square([stop_end + 0.3, stop_end + 0.3]);
  }
}

// The four corners, as a transform: children are drawn in the rear left corner,
// with the side wall along x = 0 and the rear wall along y = 0.
module corners() {
  for (m = [0, 1], n = [0, 1])
    translate([m ? S : 0, n ? Sy : 0, 0]) mirror([m, 0, 0]) mirror([0, n, 0]) children();
}

// ---- Lid patterns, all centred on the origin ----

// Honeycomb of pointy top hexagons covering a w by w area.
module hex_field2d(w) {
  p = hex_af + hex_w;
  n = ceil(w / p / 2) + 1;
  for (j = [-n : n], i = [-n : n])
    translate([(i + (j % 2 == 0 ? 0 : 0.5)) * p, j * p * cos(30)])
      rotate(90) circle(d = hex_af / cos(30), $fn = 6);
}

// Diagonal stripes of width w covering the lid.
module stripes2d(w) {
  n = ceil(Sy / dia_p);
  rotate(45) for (k = [-n : n]) translate([k * dia_p - w / 2, -Sy]) square([w, 2 * Sy]);
}

// The recessed groove network of the relief.
module grooves2d() {
  if (lid_pattern == "hex")
    difference() { square(2 * Sy, center = true); hex_field2d(Sy); }
  else if (lid_pattern == "ripple")
    for (r = [rip_p : rip_p : Sy]) annulus2d(r, r + rip_w);
  else
    stripes2d(dia_w);
}

// The same pattern cut through over the fan.
module fan_open2d() {
  d = fan_size - 4;
  if (lid_pattern == "hex")
    intersection() { circle(d = d); hex_field2d(fan_size); }
  else if (lid_pattern == "ripple")
    difference() {
      intersection() {
        circle(d = d);
        for (r = [rip_p : rip_p : d / 2]) annulus2d(r - 0.5, r + rip_w + 0.5);
      }
      for (a = [0, 90]) rotate(a) square([fan_size, 2.5], center = true);
    }
  else
    intersection() { circle(d = d); stripes2d(dia_p - 3); }
}

// ---- Shared shell ----

module body(h, ch) {
  hull() {
    linear_extrude(h - ch) outer2d();
    translate([0, 0, h - 0.01]) linear_extrude(0.01) inset2d(ch);
  }
}

module shell(h, wt, has_floor, has_lip, cap, ch) {
  cav_z = has_floor ? z0 : -1;
  cav_h = cap > 0 ? h - cap - cav_z : h + lip_h + 2;
  union() {
    difference() {
      body(h, ch);
      // cavity
      translate([0, 0, cav_z]) linear_extrude(cav_h) inset2d(wt);
      // pocket ring for the lip of the module below
      translate([0, 0, -1]) linear_extrude(lip_h + 1) ring2d(skirt_t, rib_in);
      // hollow under the floor, leaving the rib grid
      if (has_floor)
        translate([0, 0, -1]) linear_extrude(lip_h + 1)
          difference() { inset2d(cell_in); ribs2d(); }
    }
    linear_extrude(lip_h) stops2d();
    if (has_lip) {
      translate([0, 0, h]) linear_extrude(lip_h - 0.3) lip2d(wt);
      corner_bosses(h);
    }
  }
}

// A boss in each top corner. An M3 nut slides in from the side and is trapped under
// nut_top of material; the boss tapers at 45 degrees from the side wall so it prints
// without support.
module corner_bosses(h) {
  corners() difference() {
    hull() {
      translate([wall - 0.01, wall - 0.01, h - boss_h]) cube([bs, bs, boss_h]);
      translate([wall - 0.01, wall - 0.01, h - boss_h - bs]) cube([0.02, bs, 0.02]);
    }
    translate([bc, bc, h - boss_h - bs - 1]) cylinder(d = bolt_d, h = boss_h + bs + 2);
    translate([bc - nut_af / 2, bc - nut_ac / 2, h - nut_top - nut_h]) cube([nut_af, 20, nut_h]);
  }
}

// Bolt holes through the floor corners: down into the bosses of the module below,
// or into the feet under the base.
module floor_bolt_holes() {
  corners() translate([bc, bc, -1]) cylinder(d = bolt_d, h = z0 + 2);
}

module floor_slots(ys, w) {
  for (y = ys)
    translate([wall + 10, y, lip_h]) cube([S - 2 * wall - 20, w, floor_t + 1]);
}

// Intake band on both side walls: rows of horizontal dashes, or vertical slots.
module side_vents(h, with_jack) {
  if (vent_style == "vertical") {
    vh = min(vent_h, h - vent_z - 6);
    for (m = [0, 1], y = [Sy / 2 - vent_span / 2 : vent_pitch : Sy / 2 + vent_span / 2 + 0.01])
      if (!(with_jack && jack_d > 0 && jack_pos != "rear" && ((jack_pos == "right") == (m == 1)) && abs(y - jack_x) < jack_d / 2 + 5))
        translate([m ? S - wall - 1 : -1, y - vent_w / 2, vent_z]) cube([wall + 2, vent_w, vh]);
  } else {
    dp = vent_dash + vent_gap;
    n = max(1, floor((vent_span + vent_gap) / dp));
    y0 = Sy / 2 - (n * dp - vent_gap) / 2;
    rows = min(vent_rows, floor((h - vent_z - 6) / vent_rp));
    for (m = [0, 1], r = [0 : rows - 1], k = [0 : n - 1])
      if (!(with_jack && jack_d > 0 && jack_pos != "rear" && ((jack_pos == "right") == (m == 1)) && abs(y0 + k * dp + vent_dash / 2 - jack_x) < jack_d / 2 + vent_dash / 2 + 3))
        translate([m ? S - wall - 1 : -1, y0 + k * dp, vent_z + r * vent_rp]) cube([wall + 2, vent_dash, vent_w]);
  }
}

// ---- Board module ----

module standoffs() {
  for (hh = holes)
    translate([wall + board_clear + hh[0], wall + board_clear + hh[1], z0 - 0.01])
      difference() {
        cylinder(d = 7, h = standoff_h + 0.01);
        translate([0, 0, 1]) cylinder(d = standoff_hole, h = standoff_h + 1);
      }
}

module board_module() {
  difference() {
    union() {
      difference() {
        shell(board_h, wall, true, true, 0, edge_ch);
        floor_slots([wall + 12 : 9 : Sy - wall - 12], 3);
      }
      standoffs();
    }
    floor_bolt_holes();
    // rear open above the board, the ports run edge to edge
    translate([wall - 0.01, -1, rear_top])
      cube([S - 2 * wall + 0.02, wall + 1.01, board_h + lip_h + 2]);
    // grooves the rear shield slides down into
    for (m = [0, 1])
      translate([m ? S - wall - 0.01 : wall - groove_d, 1.0, rear_top])
        cube([groove_d + 0.01, shield_t + 0.2, board_h + lip_h + 2]);
    // front wall thinned over the pico PSU
    if (front_relief)
      translate([wall + board_clear + psu_x0, Sy - wall - 0.01, board_z + 2])
        cube([psu_x1 - psu_x0, wall - relief_t + 0.01, board_h - board_z - 6]);
    if (button_d > 0) {
      translate([button_x, Sy - wall - 1, button_z]) rotate([-90, 0, 0])
        cylinder(d = button_d + 0.3, h = wall + 2);
      if (button_ring)
        translate([button_x, Sy - 1, button_z]) rotate([-90, 0, 0])
          cylinder(d = button_d + 12, h = 2);
    }
    if (jack_d > 0 && jack_pos != "rear")
      translate([jack_pos == "right" ? S - wall - 1 : -1, jack_x, jack_z]) rotate([0, 90, 0])
        cylinder(d = jack_d + 0.3, h = wall + 2);
    if (vents) side_vents(board_h, true);
  }
}

// A thin frame with the four standoff holes, to lay the board on before printing.
module board_gauge() {
  difference() {
    linear_extrude(1.2) difference() { square(board); translate([30, 30]) square(board - 60); }
    for (hh = holes) translate([hh[0], hh[1], -1]) cylinder(d = bolt_d, h = 4);
    translate([board / 2, 8, 0.6]) linear_extrude(1) text("REAR", size = 7, halign = "center");
    translate([board / 2, board - 15, 0.6]) linear_extrude(1) text("FRONT", size = 7, halign = "center");
  }
}

// ---- Bay module ----
// A floor grid of bosses on the 18 mm rib pitch, each with a self tapping M3 hole
// that goes through the floor. Anything with holes on the same pitch bolts down
// anywhere on the floor, or hangs under it.

module grid_bosses() {
  for (i = [0 : 8], j = [1 : 9]) {
    x = grid_p * i + 9;
    y = grid_p * j + 9;
    if (x < S - wall - 6 && y < Sy - wall - 6)
      translate([x, y, z0 - 0.01]) difference() {
        cylinder(d = 7, h = grid_boss_h + 0.01);
        translate([0, 0, -z0]) cylinder(d = 2.6, h = z0 + grid_boss_h + 2);
      }
  }
}

module bay_module() {
  difference() {
    union() {
      difference() {
        shell(bay_h, wall, true, true, 0, edge_ch);
        // two vent slots per grid cell, between the bosses and the ribs
        floor_slots([32 : grid_p : Sy - wall - 8], 2);
        floor_slots([38 : grid_p : Sy - wall - 8], 2);
      }
      grid_bosses();
    }
    floor_bolt_holes();
    // cable pass-through behind the drive
    translate([S / 2 - 55, wall - 0.01, -1]) cube([110, tray_y - wall, z0 + 2]);
    if (vents) side_vents(bay_h, false);
  }
}

// ---- Drive tray ----
// A frame the 3.5" drive screws onto from below through its bottom holes (SFF-8301),
// with flanges either side that bolt to the bay grid. Drawn flat, drive rear edge at
// y = 0, drive left edge at x = 0. With pads it hangs under a bay floor instead: the
// pads reach up between the ribs, the drive hangs upside down below the tray.

module tray_35(pads = 0) {
  x0 = tray_fx - 6;
  tw = tray_span + 12;
  difference() {
    union() {
      translate([x0, 0, 0]) cube([tw, tray_l, tray_t]);
      if (pads > 0)
        for (x = [tray_fx, tray_fx + tray_span], y = [9 : grid_p : tray_l - 5])
          translate([x, y, tray_t - 0.01]) cylinder(d = 7, h = pads + 0.01);
    }
    // open centre, air reaches the drive board
    translate([12, 12, -1]) cube([hdd_w - 24, tray_l - 24, tray_t + 2]);
    // grid holes in the flanges
    for (x = [tray_fx, tray_fx + tray_span], y = [9 : grid_p : tray_l - 5])
      translate([x, y, -1]) cylinder(d = bolt_d, h = tray_t + pads + 2);
    // drive screw slots: the required pair and both optional pairs
    for (x = [3.18, 3.18 + 95.25], y = [41.28, 76.2, 101.6])
      hull() for (dy = [-1.2, 1.2])
        translate([x, y + dy, -1]) cylinder(d = 3.7, h = tray_t + 2);
  }
}

// ---- Foot ----
// Follows the case corner, plugs into a corner cell of the rib grid and bolts through
// the floor hole. A recess underneath takes a 10 mm stick-on rubber pad. Drawn in the
// rear left corner, pad down.

module foot_pad2d(k) {
  offset(r = max(corner_r - k, 0.01)) offset(delta = -corner_r) translate([0.4, 0.4]) square(foot_s);
}

module foot() {
  difference() {
    union() {
      hull() {
        linear_extrude(0.01) foot_pad2d(1);
        translate([0, 0, 1]) linear_extrude(foot_h - 1) foot_pad2d(0);
      }
      translate([cell_in + 0.3, cell_in + 0.3, foot_h - 0.01]) cube([plug, plug, lip_h - 0.3]);
    }
    translate([bc, bc, -1]) cylinder(d = bolt_d, h = foot_h + lip_h + 2);
    translate([bc - nut_af / 2, bc - nut_ac / 2, foot_h - nut_top - nut_h]) cube([nut_af, 20, nut_h]);
    translate([bc, bc, -1]) cylinder(d = 10.4, h = 1.6);
  }
}

// ---- Lid ----
// One relief pattern over the whole top, raised tiles with a recessed groove network,
// and the same pattern cut through over the fan. The fan hangs from four bosses under
// the plate and is screwed from the inside, so the top carries no screw heads.

module fan_bosses() {
  for (sx = [-1, 1], sy = [-1, 1])
    translate([S / 2 + sx * fan_hole / 2, Sy / 2 + sy * fan_hole / 2, 0]) children();
}

module lid() {
  difference() {
    union() {
      shell(lid_h, lid_wall, false, false, top_t, lid_ch);
      // full height columns in the corners for the long lid bolts
      corners() translate([rib_in, rib_in, 0]) cube([wall + bs - rib_in, wall + bs - rib_in, lid_h - 0.5]);
      if (fan_size > 0)
        fan_bosses() translate([0, 0, lid_h - top_t - fan_boss_h]) cylinder(d = 7, h = fan_boss_h + 0.01);
    }
    corners() {
      translate([bc, bc, -1]) cylinder(d = bolt_d, h = lid_h + 2);
      translate([bc, bc, lid_h - 7]) cylinder(d = 6.5, h = 8);
    }
    // the recessed grooves of the relief, inside the chamfer border
    if (lid_relief > 0)
      translate([0, 0, lid_h - lid_relief]) linear_extrude(lid_relief + 1)
        offset(r = 0.3) offset(r = -0.3)
          intersection() {
            inset2d(lid_ch + 2);
            translate([S / 2, Sy / 2]) grooves2d();
          }
    if (fan_size > 0) {
      // the pattern opens up over the fan
      translate([S / 2, Sy / 2, lid_h - top_t - 1]) linear_extrude(top_t + 2) fan_open2d();
      // self tapping holes for the fan screws
      fan_bosses() translate([0, 0, lid_h - top_t - fan_boss_h - 1]) cylinder(d = 2.6, h = fan_boss_h + 2);
    }
  }
}

// ---- Rear shield ----
// Modelled flat: x along the case width, y up the case, z inward.

module rear_shield() {
  sw = S - 2 * wall + 2 * groove_d - 0.3;
  sh = board_h - rear_top;
  bx = groove_d + board_clear - 0.15;
  lip_in = stop_len + groove_d + 0.15;
  difference() {
    union() {
      cube([sw, sh, shield_t]);
      // the rear lip of the board module lives on the shield
      translate([lip_in, sh - 0.01, 0.3])
        cube([sw - 2 * lip_in, lip_h - 0.3 + 0.01, shield_t - 0.3]);
    }
    translate([bx + io_x, -1, -1]) cube([io_w, io_h + 1, shield_t + 2]);
    if (jack_d > 0 && jack_pos == "rear")
      translate([bx + jack_x, jack_z - rear_top, -1]) cylinder(d = jack_d + 0.3, h = shield_t + 2);
  }
}

// ---- Ghost hardware ----

module ghost_board() {
  color("DarkGreen", 0.5)
    translate([wall + board_clear, wall + board_clear, board_z]) cube([board, board, pcb_t]);
}

module ghost_hdd(x, z) {
  color("Silver", 0.5)
    translate([x, tray_y, z]) cube([hdd_w, hdd_l, hdd_h]);
}

module ghost_fan() {
  color("DimGray", 0.5)
    translate([S / 2 - fan_size / 2, Sy / 2 - fan_size / 2, lid_h - top_t - fan_boss_h - fan_t])
      difference() { cube([fan_size, fan_size, fan_t]); translate([fan_size / 2, fan_size / 2, -1]) cylinder(d = fan_size - 4, h = fan_t + 2); }
}

// ---- Test coupons ----
// The rear left corner of the board module and of a bay module, cut test_size square,
// the matching end of the rear shield and one foot. The board corner carries a lip,
// the shield grooves, a standoff and a nut boss; the bay corner a pocket, a stop, a
// floor bolt hole and a grid boss. Stack, slide, bolt and screw: every fit in one go.

module corner_cut(s) {
  intersection() {
    children();
    translate([-1, -1, -1]) cube([s + 1, s + 1, 300]);
  }
}

module test_layout() {
  corner_cut(test_size) board_module();
  translate([test_size + 12, 0, 0]) corner_cut(test_size) bay_module();
  translate([2 * test_size + 24, 0, 0]) corner_cut(test_size) rear_shield();
  translate([2 * test_size + 24, board_h + 10, 0]) foot();
}

// ---- Layout ----

module assembly() {
  color(color_case) board_module();
  color(color_case) corners() translate([0, 0, -foot_h - explode / 2]) foot();
  color(color_case)
    translate([wall - groove_d + 0.15, 1.1 + shield_t, rear_top]) rotate([90, 0, 0]) rear_shield();
  if (show_hardware) ghost_board();
  if (bay_modules > 0)
    for (i = [0 : bay_modules - 1])
      translate([0, 0, board_h + i * bay_h + (i + 1) * explode]) {
        color(color_case) bay_module();
        color(color_case) translate([tray_x, tray_y, z0 + grid_boss_h]) tray_35();
        if (show_hardware) ghost_hdd(tray_x, z0 + grid_boss_h + tray_t);
        if (i == 0 && hang_hdd) {
          color(color_case) translate([hang_x, tray_y, -0.3 - tray_t]) tray_35(hang_pad);
          if (show_hardware) ghost_hdd(hang_x, -0.3 - tray_t - hdd_h);
        }
      }
  translate([0, 0, board_h + bay_modules * bay_h + (bay_modules + 1) * explode]) {
    color(color_case) lid();
    if (show_hardware && fan_size > 0) ghost_fan();
  }
}

if (test_print) color(color_case) test_layout();
else if (part == "board_module") color(color_case) board_module();
else if (part == "bay_module") color(color_case) bay_module();
else if (part == "tray_35") color(color_case) translate([-tray_fx + 6, 0, 0]) tray_35();
else if (part == "tray_35_hanging") color(color_case) translate([-tray_fx + 6, 0, 0]) tray_35(hang_pad);
else if (part == "lid") color(color_case) translate([0, Sy, lid_h]) rotate([180, 0, 0]) lid();
else if (part == "rear_shield") color(color_case) rear_shield();
else if (part == "foot") color(color_case) foot();
else if (part == "board_gauge") color(color_case) board_gauge();
else assembly();