Concept only

scad/YOOPAI_round_to_rectangular_duct_transition_adapter.scad

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+//
+// duct_round_to_window_slot.scad
+// 20260321 ChatGPT
+// $Id$
+// $HeadURL$
+//
+// Example command lines:
+//
+//   openscad -o duct_round_to_window_slot_20260321_1830.stl duct_round_to_window_slot.scad
+//
+//   openscad \
+//     -D 'round_stub_od=72.0' \
+//     -D 'round_fit_clearance=0.6' \
+//     -D 'slot_h=25.4' \
+//     -D 'slot_w=162.0' \
+//     -D 'wall=2.4' \
+//     -D 'round_stub_len=30' \
+//     -D 'transition_len=140' \
+//     -D 'slot_stub_len=30' \
+//     -o duct_round_to_window_slot_20260321_1831.stl \
+//     duct_round_to_window_slot.scad
+//
+
+$fn = 128;
+
+// ------------------------------------------------------------
+// PARAMETERS
+// ------------------------------------------------------------
+
+// Measured OD of the existing plastic tent outlet that your flex duct
+// currently wraps around.
+round_stub_od = 72.0;
+
+// Extra diameter added so the flex duct can slip over this printed stub.
+// Start with 0.4 to 0.8 mm and adjust after a test print.
+round_fit_clearance = 0.6;
+
+// Wall thickness
+wall = 2.4;
+
+// Length of straight circular collar for flex duct attachment
+round_stub_len = 30;
+
+// Length of tapered transition body
+transition_len = 140;
+
+// Length of straight rectangular outlet section for insertion under window
+slot_stub_len = 30;
+
+// Window slot internal size
+slot_h = 25.4;      // 1.0 inch
+slot_w = 162.0;     // approximately area-preserving for 72 mm round
+
+// Corner radius for rounded rectangle, internal passage
+slot_r = 6.0;
+
+// Optional lip / stop ring on circular end so the duct has something
+// to register against before clamp/strap tightening.
+add_round_stop_ring = true;
+round_stop_ring_len = 5.0;
+round_stop_ring_extra_od = 6.0;
+
+
+// ------------------------------------------------------------
+// DERIVED VALUES
+// ------------------------------------------------------------
+
+// This is the OD of the printed round collar that the flexible duct
+// will fit around.
+round_outer_d = round_stub_od + round_fit_clearance;
+
+// Inner flow diameter at the round side
+round_inner_d = round_outer_d - 2*wall;
+
+// Outer dimensions of the rectangular outlet
+slot_outer_h = slot_h + 2*wall;
+slot_outer_w = slot_w + 2*wall;
+slot_outer_r = slot_r + wall;
+
+// Z locations
+z0 = 0;
+z1 = round_stub_len;
+z2 = round_stub_len + transition_len;
+z3 = round_stub_len + transition_len + slot_stub_len;
+
+
+// ------------------------------------------------------------
+// HELPERS
+// ------------------------------------------------------------
+
+module rounded_rect_2d(w, h, r) {
+    rr = min(r, min(w,h)/2 - 0.01);
+    hull() {
+        translate([-(w/2 - rr), -(h/2 - rr)]) circle(r=rr);
+        translate([ +(w/2 - rr), -(h/2 - rr)]) circle(r=rr);
+        translate([-(w/2 - rr), +(h/2 - rr)]) circle(r=rr);
+        translate([ +(w/2 - rr), +(h/2 - rr)]) circle(r=rr);
+    }
+}
+
+module round_profile_3d(d, z, h=1) {
+    translate([0,0,z])
+        linear_extrude(height=h)
+            circle(d=d);
+}
+
+module rect_profile_3d(w, h_rect, r, z, h=1) {
+    translate([0,0,z])
+        linear_extrude(height=h)
+            rounded_rect_2d(w, h_rect, r);
+}
+
+
+// ------------------------------------------------------------
+// OUTER SHELL
+// ------------------------------------------------------------
+
+module outer_shell() {
+    union() {
+        // Straight round collar
+        hull() {
+            round_profile_3d(round_outer_d, z0, 1);
+            round_profile_3d(round_outer_d, z1, 1);
+        }
+
+        // Transition
+        hull() {
+            round_profile_3d(round_outer_d, z1, 1);
+            rect_profile_3d(slot_outer_w, slot_outer_h, slot_outer_r, z2, 1);
+        }
+
+        // Straight rectangular collar
+        hull() {
+            rect_profile_3d(slot_outer_w, slot_outer_h, slot_outer_r, z2, 1);
+            rect_profile_3d(slot_outer_w, slot_outer_h, slot_outer_r, z3, 1);
+        }
+    }
+}
+
+
+// ------------------------------------------------------------
+// INNER VOID
+// ------------------------------------------------------------
+
+module inner_void() {
+    union() {
+        // Straight round passage
+        hull() {
+            round_profile_3d(round_inner_d, z0 - 0.2, 1.4);
+            round_profile_3d(round_inner_d, z1 + 0.2, 1.4);
+        }
+
+        // Transition passage
+        hull() {
+            round_profile_3d(round_inner_d, z1 - 0.2, 1.4);
+            rect_profile_3d(slot_w, slot_h, slot_r, z2 + 0.2, 1.4);
+        }
+
+        // Straight rectangular passage
+        hull() {
+            rect_profile_3d(slot_w, slot_h, slot_r, z2 - 0.2, 1.4);
+            rect_profile_3d(slot_w, slot_h, slot_r, z3 + 0.2, 1.4);
+        }
+    }
+}
+
+
+// ------------------------------------------------------------
+// OPTIONAL ROUND STOP RING
+// ------------------------------------------------------------
+
+module round_stop_ring() {
+    if (add_round_stop_ring) {
+        translate([0,0,z0]) {
+            difference() {
+                cylinder(d = round_outer_d + round_stop_ring_extra_od,
+                         h = round_stop_ring_len);
+                translate([0,0,-0.2])
+                    cylinder(d = round_outer_d,
+                             h = round_stop_ring_len + 0.4);
+            }
+        }
+    }
+}
+
+
+// ------------------------------------------------------------
+// FINAL PART
+// ------------------------------------------------------------
+
+union() {
+    difference() {
+        outer_shell();
+        inner_void();
+    }
+    round_stop_ring();
+}