improve clip in strength

pill_container/pill_container.scad

@@ -8,12 +8,12 @@
 cases = 4;
 // Inner size of each compartment: X * X * X (mm)
 X = 20;
-// Text engraved on the lid
+// Text engraved on the lid (runs parallel to the sliding direction)
 engraving = "Monday";
 
 /* [Engraving] */
 text_size  = 6;
-text_depth = 0.6;
+text_depth = 0.6;   // engraved with sloped walls (see dt_ang)
 text_font  = "Overpass:style=Bold";
 
 /* [Structure] */
@@ -21,33 +21,39 @@ wall        = 3.2;   // outer side walls and front wall
 divider     = 1.6;   // wall between compartments
 floor_t     = 1.6;   // floor thickness
 lid_h       = 3.0;   // lid thickness
-rail_ledge  = 2.4;   // width of the ledge the lid edges rest on (< wall)
+rail_ledge  = 1.4;   // width of the ledge the lid edges rest on (< wall)
 end_wall    = 5.5;   // rear wall thickness (holds the clip groove)
 corner_r    = 1.5;   // vertical corner rounding
 
-/* [Tolerances] */
+/* [Dovetail] */
-// Sliding clearance between lid and box
+// Angle of the sliding faces from vertical = worst overhang of the print.
+// 30 prints cleanly without supports; lower = even safer but less grip.
+dt_ang = 30;   // [15:1:45]
+
+/* [Fit] */
+// Sliding clearance between lid and box (PETG: 0.2 - 0.3)
 tol      = 0.25;
 // Clearance inside the snap pockets (smaller = tighter, less rattle)
 snap_tol = 0.15;
 
 /* [Snap] */
+// Length of the slots in the lid = length of the flexible tab and arms.
+clip_len     = 11.4;
 // Rear bump: how far it is pushed aside while sliding (click strength)
-detent       = 0.7;
+detent       = 0.5;
-// Side bumps: same, but sideways
+// Side ridges: same, but sideways
-side_detent  = 0.6;
+side_detent  = 0.5;
-// Side bump length along the lid face
+// Flexible tab (rear bump): width, thickness, slot width
-side_len     = 1.8;
+clip_w       = 5;
-// Flexible tab (rear bump): width, max length, slot width
+tab_t        = 1.2;   // thinner = softer (the underside of the tab is relieved)
-clip_w       = 4.5;
-clip_len_max = 28;
 clip_slot    = 1.0;
-// Flexible side arms: thickness (stiffness) and slot width
+// Flexible side arms: thickness (stiffness) and slot width, both measured
-arm_t        = 1.6;
+// perpendicular to the sloped faces
+arm_t        = 1.2;
 arm_slot     = 1.2;
 
 /* [Display] */
-// plate = both parts laid out for printing, assembly = closed for preview
+// plate = both parts laid out for printing, assembly = closed, for preview
 part       = "plate"; // [plate, box, lid, assembly]
 // Assembly preview only: push the lid open by this many mm
 lid_offset = 0;
@@ -58,6 +64,9 @@ lid_offset = 0;
 $fn = 48;
 eps = 0.01;
 
+m   = tan(dt_ang);                               // sideways shift per mm of height
+cs  = cos(dt_ang);
+
 W         = X + 2*wall;                          // outer width (Y)
 x_cav_end = wall + cases*X + (cases-1)*divider;  // end of last compartment
 L         = x_cav_end + end_wall;                // outer length (X)
@@ -65,35 +74,43 @@ z0        = floor_t + X;                         // top of compartments
 hg        = lid_h + tol;                         // height of the lid groove
 H         = z0 + hg;                             // total height
 gb        = X/2 + rail_ledge;                    // groove half width at z0
-k45       = tol*sqrt(2);                         // horizontal offset = tol on a 45 deg face
+k         = tol/cs;                              // horizontal gap = tol on the sloped faces
-lw_b      = gb - tol - k45;                      // lid half width at its bottom
+lw_b      = gb - m*tol - k;                      // lid half width at its bottom
-lw_t      = gb - hg - k45;                       // lid half width at its top
+lw_t      = gb - m*hg  - k;                      // lid half width at its top
+d1        = arm_t/cs;                            // horizontal offsets of the arm slot
+d2        = (arm_t + arm_slot)/cs;               //   walls from the sloped face
 
 lid_x0    = wall + tol;                          // lid front (closed position)
 lid_len   = L - lid_x0;                          // lid rear is flush with box rear
-clip_len  = min(clip_len_max, lid_len*0.45);     // tab and arm length
+tab_r     = lid_h - tab_t;                       // relief under the tab (softens it)
+
+// Engraving: shrink the text if it would not fit between the lid front
+// and the slots (average bold glyph is ~0.9 * text_size wide, conservative)
+text_zone = lid_len - clip_len - 2*2;            // 2 mm margin at both ends
+text_fit  = min(text_size, text_zone/(len(engraving)*0.9));
 
 bump_h    = tol + detent;                        // rear V bump height
-sb_h      = tol + side_detent;                   // side bump height
+sb_h      = tol + side_detent;                   // side ridge height
 cham      = detent + tol;                        // lead-in chamfer on rear wall
 xb        = x_cav_end + (end_wall - cham)/2;     // x of all detents
-
+zm        = tol + lid_h/2;                       // mid height of the lid faces
-// Height (above z0) of the side bump centre on the sloped lid face, chosen so that bump and dimple stay clear of the groove bottom and of the rail top
-sb_hl  = side_len/2 + snap_tol;
-sb_up  = sqrt(0.5)*(sb_hl + sb_h + snap_tol);
-sb_dn  = sqrt(0.5)*(sb_hl + 0.2 + snap_tol);
-zs_lo  = 0.15 + sb_dn;
-zs_hi  = hg - 0.35 - sb_up;
-zs     = (zs_lo + zs_hi)/2;
 
 assert(cases >= 1, "cases must be >= 1");
-assert(rail_ledge < wall, "rail_ledge must be smaller than wall");
+assert(dt_ang >= 15 && dt_ang <= 45, "dt_ang must be between 15 and 45");
-assert(zs_lo <= zs_hi, "Lid too thin for the side bumps: increase lid_h or reduce side_len / side_detent");
+assert(rail_ledge < wall - 1, "rail_ledge must be at least 1 mm smaller than wall");
+assert(m*lid_h - k >= 1, "Dovetail grip too small: increase lid_h or dt_ang");
 assert(arm_slot > side_detent + 0.2, "arm_slot must exceed side_detent + 0.2");
-assert(clip_w/2 + clip_slot + 1.2 < lw_t - (arm_t + arm_slot)*sqrt(2),
+assert(lw_t - d2 - (clip_w/2 + clip_slot) >= 1.2,
-       "Tab, slots and side arms do not fit in the lid (X is too small, about 20 mm minimum with default settings): decrease clip_w / clip_slot / arm_t / arm_slot or increase X");
+       "Tab, slots and side arms do not fit in the lid (X too small, about 18 mm minimum with default settings): reduce clip_w / clip_slot / arm_t / arm_slot or increase X");
+assert(tab_t >= 0.8 && tab_t <= lid_h, "tab_t must be between 0.8 and lid_h");
+assert(lid_len >= clip_len + 8, "Lid too short for this clip_len: reduce clip_len");
+assert(text_zone > 4, "Lid too short for any engraving: reduce clip_len");
 
 echo(str("Outer size: ", L, " x ", W, " x ", H, " mm"));
+if (text_fit < text_size)
+    echo(str("Engraving scaled down from size ", text_size, " to ", text_fit));
+if (text_fit < 3)
+    echo("WARNING: engraving is very small; use fewer characters, more cases or a shorter clip_len");
 
 // ---------------------------------------------------------------------
 //  Helpers
@@ -102,7 +119,7 @@ echo(str("Outer size: ", L, " x ", W, " x ", H, " mm"));
 module yz_extrude(len) {
     rotate([90, 0, 90]) linear_extrude(height = len) children();
 }
-// Extrude a 2D (x,z) profile along Y, centered on y = 0
+// Extrude a 2D (x,z) profile along Y, centred on y = 0
 module xz_extrude(w) {
     rotate([90, 0, 0]) linear_extrude(height = w, center = true) children();
 }
@@ -110,27 +127,20 @@ module rrect(l, w, r) {
     translate([0, -w/2]) offset(r = r) offset(delta = -r) square([l, w]);
 }
 
-// Side bump
+// Side ridge profile: x = sliding direction, y = face normal.
-module side_bump_3d(extra = 0) {
+// It runs along the whole sloped face (no end faces -> no overhang).
-    h = sb_h + extra;
+module side_bump_2d() {
-    len = side_len + extra*2;
+    polygon([[-sb_h, -0.3], [sb_h, -0.3], [sb_h, 0], [0, sb_h], [-sb_h, 0]]);
-    
-    // Pyramid pointing outwards in local +Y
-    rotate([-90, 0, 0])
-        scale([1, len/(2*h), 1])
-        cylinder(h = h, r1 = h, r2 = 0, $fn = 4);
-        
-    // Embedded base
-    translate([0, -0.2, 0])
-        rotate([-90, 0, 0])
-        scale([1, len/(2*h), 1])
-        cylinder(h = 0.2, r1 = h, r2 = h, $fn = 4);
 }
-
+module side_prism(grow = 0) {
+    linear_extrude(height = hg/cs + 4, center = true)
+        offset(delta = grow) side_bump_2d();
+}
+// Place children on the middle of the lid's sloped face
 module on_side(s) {   // s = +1 right side, -1 left side
-    translate([xb, s*(lw_b - (zs - tol)), z0 + zs])
+    translate([xb, s*(gb - m*zm - k), z0 + zm])
-        if (s > 0) rotate([45, 0, 0]) children();
+        if (s > 0) rotate([dt_ang, 0, 0]) children();
-        else mirror([0, 1, 0]) rotate([45, 0, 0]) children();
+        else mirror([0, 1, 0]) rotate([dt_ang, 0, 0]) children();
 }
 
 // ---------------------------------------------------------------------
@@ -149,8 +159,8 @@ module box() {
         translate([wall, 0, z0])
             yz_extrude(L - wall + eps)
                 polygon([[-gb, 0], [gb, 0],
-                         [ gb - hg - eps, hg + eps],
+                         [ gb - m*(hg + eps), hg + eps],
-                         [-(gb - hg - eps), hg + eps]]);
+                         [-(gb - m*(hg + eps)), hg + eps]]);
 
         // V groove in the rear wall for the tab bump
         translate([xb, 0, 0])
@@ -160,9 +170,11 @@ module box() {
                              [ bump_h, z0 + tol],
                              [ 0,      z0 + tol - bump_h]]);
 
-        // dimples in the rails for the side bumps
+        // V channels along the rail faces for the side ridges
-        for (s = [-1, 1]) on_side(s)
+        intersection() {
-            side_bump_3d(snap_tol);
+            union() for (s = [-1, 1]) on_side(s) side_prism(snap_tol);
+            translate([xb - 5, -W, z0]) cube([10, 2*W, hg + 1]);
+        }
 
         // lead-in chamfer so the tab bump can climb onto the rear wall
         xz_extrude(X)
@@ -173,48 +185,65 @@ module box() {
     }
 }
 
+// Engraving
+engr_slices = 6;
+module engraving_cut(tx) {
+    dz = text_depth/engr_slices;
+    for (i = [0 : engr_slices - 1])
+        translate([tx, 0, z0 + hg - (i + 1)*dz])
+            linear_extrude(dz + eps)
+                offset(delta = -i*dz*tan(dt_ang))
+                    text(engraving, size = text_fit, font = text_font,
+                         halign = "center", valign = "center");
+}
+
 // ---------------------------------------------------------------------
-//  Lid
+//  Lid (modelled in its closed position, engraved face up)
 // ---------------------------------------------------------------------
 module lid(bumps = true) {
     text_x = (lid_x0 + L - clip_len)/2;
-    d1 = arm_t*sqrt(2);
-    d2 = (arm_t + arm_slot)*sqrt(2);
     za = tol - 1;
     zb = hg + 1;
-    // x-offset of the side face at height z (right side)
+    // y of the right sloped face, moved inwards by d (horizontal), at height z
-    function yf(z, d) = lw_b - (z - tol) - d;
+    function yf(z, d) = lw_b - m*(z - tol) - d;
 
     difference() {
         union() {
-            // lid plate (dovetail profile)
+            // lid plate (dovetail profile), underside of the tab relieved
+            difference() {
                 translate([lid_x0, 0, z0])
                     yz_extrude(lid_len)
                         polygon([[-lw_b, tol], [lw_b, tol],
                                  [ lw_t, hg],  [-lw_t, hg]]);
+                translate([L - clip_len, -(clip_w/2 + clip_slot), z0 + tol - 1])
+                    cube([clip_len + 1, clip_w + 2*clip_slot, 1 + tab_r]);
+            }
 
             if (bumps) {
-                // V bump under the free end of the tab
+                // V bump under the free end of the tab (45 deg flanks, grows
+                // from the relieved underside, apex at the same height as before)
                 translate([xb, 0, 0])
                     xz_extrude(clip_w)
-                        polygon([[-bump_h, z0 + tol + eps],
+                        polygon([[-(bump_h + tab_r), z0 + tol + tab_r + eps],
-                                 [ bump_h, z0 + tol + eps],
+                                 [  bump_h + tab_r,  z0 + tol + tab_r + eps],
                                  [ 0,                z0 + tol - bump_h]]);
-                
+                // side ridges, cut flush with the lid top and bottom planes
-                // side bumps on the flexible arms
+                intersection() {
-                for (s = [-1, 1]) on_side(s)
+                    union() for (s = [-1, 1]) on_side(s) side_prism(0);
-                    side_bump_3d(0);
+                    translate([xb - 5, -W/2, z0 + tol]) cube([10, W, lid_h]);
+                }
             }
         }
 
-        // slots that free the central tab
+        // slots that free the central tab (vertical walls)
         for (s = [-1, 1])
             translate([L - clip_len,
                        s*(clip_w/2 + clip_slot/2) - clip_slot/2,
                        z0 - 1])
                 cube([clip_len + 1, clip_slot, hg + 2]);
 
-        // slots (parallel to the sloped faces) that free the side arms
+        // slots that free the side arms, parallel to the sloped faces so the
+        // arms keep a constant thickness (same angle as the dovetail)
         for (s = [-1, 1])
             translate([L - clip_len, 0, z0])
                 yz_extrude(clip_len + 1)
@@ -223,10 +252,7 @@ module lid(bumps = true) {
                                  [yf(zb, d2), zb], [yf(za, d2), za]]);
 
         // engraving, parallel to the sliding direction
-        translate([text_x, 0, z0 + hg - text_depth])
+        engraving_cut(text_x);
-            linear_extrude(text_depth + eps)
-                text(engraving, size = text_size, font = text_font,
-                     halign = "center", valign = "center");
     }
 }