docs: Add a square_tower.scad and stl print object

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

docs/prints/square_tower.scad

@@ -0,0 +1,63 @@
+// Calibration test tower
+//
+// Generate STL using OpenSCAD:
+//   openscad square_tower.scad -o square_tower.stl
+
+square_width = 5;
+square_size = 60;
+square_height = 50;
+antiwarp_height = .8;
+antiwarp_radius = 5;
+
+module square_with_anti_warp() {
+    module anti_warp_cylinder() {
+        cylinder(r=antiwarp_radius, h=antiwarp_height, $fs=.5);
+    }
+    cube([square_size, square_size, square_height]);
+    dist = antiwarp_radius / 2.5;
+    translate([dist, dist, 0])
+        anti_warp_cylinder();
+    translate([square_size-dist, dist, 0])
+        anti_warp_cylinder();
+    translate([dist, square_size-dist, 0])
+        anti_warp_cylinder();
+    translate([square_size-dist, square_size-dist, 0])
+        anti_warp_cylinder();
+}
+
+module hollow_square() {
+    difference() {
+        square_with_anti_warp();
+        translate([square_width, square_width, -1])
+            cube([square_size-2*square_width, square_size-2*square_width,
+                  square_height+2]);
+    }
+}
+
+module notch() {
+    CUT = 0.01;
+    depth = .5;
+    width = 1;
+    translate([-depth, -width, -CUT])
+        cube([2*depth, 2*width, square_height + 2*CUT]);
+}
+
+module square_with_notches() {
+    difference() {
+        // Start with initial square
+        hollow_square();
+        // Remove four notches on inside perimeter
+        translate([square_width, square_size/2 - 4, 0])
+            notch();
+        translate([square_size/2, square_size - square_width, 0])
+            rotate([0, 0, 90])
+                notch();
+        translate([square_size - square_width, square_size/2, 0])
+            notch();
+        translate([square_size/2, square_width, 0])
+            rotate([0, 0, 90])
+                notch();
+    }
+}
+
+square_with_notches();