Case: add TPU feet held by the base screws

Each foot has a spigot that locates in the base's screw counterbore and a
pocket for the screw head; base screws become M3x10. Base unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

case/README.md

@@ -20,6 +20,7 @@ at least 210 × 115 mm.
 | [stl/body.stl](stl/body.stl) | upside down, top on the bed (as exported) | Sides, top and back wall. No supports needed. |
 | [stl/bezel.stl](stl/bezel.stl) | face down (as exported) | Front panel with the window and the display bosses. |
 | [stl/base.stl](stl/base.stl) | flat (as exported) | Floor with the board standoffs and the screw holes. |
+| [stl/feet.stl](stl/feet.stl) | flat side down (as exported) | 4 feet, print in **TPU**. Each clamps under one of the base screws, with a spigot that locates in the screw's counterbore. |
 
 PETG is a good choice: the display warms the inside by a few degrees. PLA
 works if the case stays out of the sun.
@@ -34,7 +35,7 @@ works if the case stays out of the sun.
   - 4 on the base's board standoffs
 - 4 × M3×8 to bolt the display to the bezel
 - 4 × M3×6 to hold the D1 board on its standoffs
-- 4 × M3×8 to hold the base on, from below
+- 4 × M3×8 to hold the base on, from below; **M3×10** with the TPU feet
 
 ## Assembly
 
@@ -46,7 +47,9 @@ works if the case stays out of the sun.
 5. Connect the display cable. The MAX3232 sits inline in the cable; tie it to
    the anchor on the base.
 6. Put the body on the base and screw it together from below. The base holds
-   the bezel in place.
+   the bezel in place. With the feet, put a foot on each screw first (the
+   spigot faces the base) and use M3×10. Tighten until the foot is snug; the
+   TPU only needs light compression.
 
 ## Measure before printing
 
@@ -78,6 +81,7 @@ with:
 openscad -D 'part="body"'  --export-format binstl -o stl/body.stl  vfd-case.scad
 openscad -D 'part="bezel"' --export-format binstl -o stl/bezel.stl vfd-case.scad
 openscad -D 'part="base"'  --export-format binstl -o stl/base.stl  vfd-case.scad
+openscad -D 'part="feet"'  --export-format binstl -o stl/feet.stl  vfd-case.scad
 ```
 
 `part="assembly"` shows everything with dummy display and board models, and
@@ -85,7 +89,7 @@ openscad -D 'part="base"'  --export-format binstl -o stl/base.stl  vfd-case.scad
 each one must render as an empty object:
 
 - `check_body_bezel`, `check_body_display`, `check_bezel_display`
-- `check_body_base`, `check_bezel_base`, `check_display_base`
+- `check_body_base`, `check_bezel_base`, `check_display_base`, `check_feet_base`
 - `check_board`
 - `check_insertion`: sweeps the bezel and display along their slide-in path
   through the body.

case/vfd-case.scad

@@ -62,6 +62,14 @@ screw_d = 3.4;          // M3 clearance
 head_d = 6.2;           // M3 head counterbore in the base
 head_depth = 2;
 
+/* [TPU feet, held by the base screws (use M3x10 instead of M3x8)] */
+foot_d = 14;            // fits inside the base outline at the rear corners
+foot_h = 4.5;           // below the base
+foot_spigot_h = 1.8;    // locates in the base's screw counterbore
+foot_spigot_d = head_d - 0.2;
+foot_head_d = 6.6;      // pocket for the screw head (from below)
+foot_head_depth = 3.5;  // M3 socket head is 3 mm tall
+
 /* [WEMOS D1 R1 (Arduino UNO footprint)] */
 board_l = 68.58;        // along the case depth, connector edge at the back
 board_w = 53.34;
@@ -227,6 +235,27 @@ module base() {
 
 function board_xy(h) = [board_x0 + h[1], board_conn_y - h[0], 0];
 
+// One foot, top face at z = 0 (against the base's underside), centred on a screw.
+module foot() {
+    difference() {
+        union() {
+            translate([0, 0, -foot_h]) cylinder(d = foot_d, h = foot_h);
+            translate([0, 0, -0.01]) cylinder(d = foot_spigot_d, h = foot_spigot_h + 0.01);
+        }
+        translate([0, 0, -foot_h - 1]) cylinder(d = screw_d, h = foot_h + foot_spigot_h + 2);
+        translate([0, 0, -foot_h - 1]) cylinder(d = foot_head_d, h = foot_head_depth + 1);
+        // soften the bottom edge
+        translate([0, 0, -foot_h - 0.01]) difference() {
+            cylinder(d = foot_d + 1, h = 1);
+            cylinder(d1 = foot_d - 2, d2 = foot_d + 0.01, h = 1.01);
+        }
+    }
+}
+
+module feet_in_place() {
+    for (p = base_screws) translate([p[0], p[1], -base_t]) foot();
+}
+
 module tie_anchor() {
     difference() {
         translate([-5, -3, 0]) cube([10, 6, 5]);
@@ -265,6 +294,7 @@ if (part == "assembly") {
     color("SlateGray", 0.5) body();
     color("DimGray") bezel();
     color("Gainsboro") base();
+    color("Black") feet_in_place();
     color("SeaGreen") display_dummy();
     color("SteelBlue") board_dummy();
 } else if (part == "section") {
@@ -283,6 +313,9 @@ if (part == "assembly") {
     translate([0, depth, height]) rotate([180, 0, 0]) body();      // top on the bed
 } else if (part == "bezel") {
     translate([0, 0, -lip]) multmatrix(M) bezel();                 // front face on the bed
+} else if (part == "feet") {
+    for (i = [0 : len(base_screws) - 1])                         // 4 feet, flat side down
+        translate([i * (foot_d + 5), 0, foot_h]) foot();
 } else if (part == "base") {
     translate([0, 0, base_t]) base();
 }
@@ -294,6 +327,7 @@ else if (part == "check_body_base") intersection() { body(); base(); }
 else if (part == "check_bezel_base") intersection() { bezel(); base(); }
 else if (part == "check_board") intersection() { union() { body(); bezel(); base(); display_dummy(); } board_dummy(); }
 else if (part == "check_display_base") intersection() { base(); display_dummy(); }
+else if (part == "check_feet_base") intersection() { base(); feet_in_place(); }
 // The bezel slides in from below along the panel: sweep it (with the display) down and check.
 else if (part == "check_insertion") intersection() {
     body();