diff --git a/examples/spring_dog.scad b/examples/spring_dog.scad
new file mode 100644
index 00000000..8b4f2637
--- /dev/null
+++ b/examples/spring_dog.scad
@@ -0,0 +1,363 @@
+include <rounded_cylinder.scad>;
+include <cross_sections.scad>;
+include <rotate_p.scad>;
+include <helix_extrude.scad>;
+include <helix.scad>;
+include <circle_path.scad>;
+include <polysections.scad>;
+include <arc.scad>;
+include <ellipse_extrude.scad>;
+include <shape_ellipse.scad>;
+include <shape_glued2circles.scad>;
+include <bezier_curve.scad>;
+include <shape_pie.scad>;
+
+part = "PREVIEW"; // [FRONT, SPRING, BACK, PREVIEW]
+
+head_radius = 15;
+spring_levels = 20;
+line_thickness = 4;
+line_distance = 1.5;
+
+latch_r1 = 2.5;
+latch_r2 = 3;
+latch_h = 6;
+latch_spacing = 0.4;
+
+
+module latch_prototype(r1, r2, h) {
+    rd = r2 - r1;
+    
+    linear_extrude(h) 
+        circle(r1);
+        
+    translate([0, 0, h - rd]) 
+        rotate_extrude() 
+            translate([r2 - rd, 0, 0]) 
+                circle(rd, $fn = 4);
+}
+
+module latch_convex(r1, r2, h) {
+    rd = r2 - r1;
+    
+    difference() {
+        latch_prototype(r1, r2, h);
+        
+        translate([0, 0, rd * 2])  
+            linear_extrude(h - rd * 2) 
+                square([rd * 2, r2 * 2], center = true);
+    
+    }
+}
+
+module latch_concave(r1, r2, h, spacing) {
+    latch_prototype(r1 + spacing, r2 + spacing, h);
+    translate([0, 0, h]) 
+        linear_extrude(spacing) 
+            circle(r2);
+}
+
+
+module toy_spring(radius, levels, sides, line_thickness, line_distance) {
+    $fn = 4;
+    
+    spring = circle_path(radius = line_thickness / 2);
+
+    helix_extrude(spring, 
+        radius = radius, 
+        levels = levels, 
+        level_dist = line_thickness + line_distance,
+        $fn = sides
+    );
+    
+    if(line_distance != 0) {
+        spring_gap = circle_path(radius = line_distance / 2);
+        
+        #translate([0, 0, line_thickness / 2 + line_distance / 2])
+            helix_extrude(spring_gap, 
+                radius = radius, 
+                levels = levels, 
+                level_dist = line_thickness + line_distance,
+                $fn = sides
+            );        
+    }
+}
+
+
+module dog_back(head_r, latch_r1, latch_r2, latch_h) {
+    $fn = 36;    
+
+    module foot() {
+        translate([head_r, 0, 0]) union() {
+            color("PapayaWhip") ellipse_extrude(head_r / 3) polygon(
+                shape_ellipse([head_r / 3, head_r / 2])
+            );
+            
+            color("Maroon")  linear_extrude(head_r) circle(head_r / 8);
+            
+            color("Goldenrod") translate([head_r / 45, 0, head_r / 2]) rotate([0, -15, 0]) rounded_cylinder(
+                radius = [head_r / 5, head_r / 3.5], 
+                h = head_r * 1.25, 
+                round_r = 2
+            );            
+        }    
+    }
+
+
+    module feet() {
+        foot();
+        mirror([1, 0, 0]) foot();
+    }
+
+    module body_feet() {
+        translate([0, -head_r / 5, -head_r * 1.65]) 
+            feet();
+
+        union() {
+            color("Goldenrod") scale([1, 1.25, 1]) difference() {
+                sphere(head_r);
+                
+                translate([-head_r, head_r / 6, -head_r]) 
+                    cube(head_r * 2);
+            }
+        }
+    }
+
+    module back() {
+        mirror([0, 1, 0]) 
+            body_feet();
+        rotate([-36.5, 0, 0]) 
+            color("Goldenrod") 
+                linear_extrude(head_r * 2, scale = 0.5) 
+                    circle(head_r / 6);
+    }
+
+    back();
+        
+    color("Goldenrod")  translate([0, -head_r * 0.2, 0]) 
+        rotate([90, 0, 0]) 
+            latch_convex(latch_r1, latch_r2, latch_h);
+}
+
+module spring_dog_spring(head_r, spring_levels, line_thickness, line_distance, latch_r1, latch_r2, latch_h, latch_spacing) {
+    spring_sides = 36;
+    h = spring_levels * line_thickness;
+
+    module latch_plate_back() {
+        difference() {
+            linear_extrude(latch_h + latch_spacing) 
+                circle(head_r);  
+            
+            latch_concave(latch_r1, latch_r2, latch_h, latch_spacing, $fn = spring_sides);
+        }         
+    }
+
+    module latch_plate_front() {
+        linear_extrude(latch_h + latch_spacing) 
+            circle(head_r);  
+        
+        translate([0, 0, latch_h + latch_spacing]) 
+            latch_convex(latch_r1, latch_r2, latch_h, $fn = spring_sides);      
+    }    
+    
+    color("yellow") union() {
+        latch_plate_back();
+        
+        translate([0, 0, line_thickness / 2])  toy_spring(
+            head_r - line_thickness / 1.5, 
+            spring_levels, 
+            spring_sides, 
+            line_thickness,
+            line_distance
+        );
+        
+        translate([0, 0, h + line_distance * spring_levels]) 
+            latch_plate_front();
+    }
+}
+
+module dog_front(head_r, latch_r1, latch_r2, latch_h, latch_spacing) {
+    $fn = 36;
+    
+    module head() {
+
+        module head_nose() {
+            color("Goldenrod") 
+                rotate([-15, 0, 0]) 
+                    scale([1, 0.9, 0.9]) 
+                        sphere(head_r);
+
+            // nose
+            color("PapayaWhip") 
+                translate([0, -head_r * 0.45, -head_r / 5]) 
+                    rotate([85, 0, 0]) 
+                        scale([1.25, 0.8, 1]) 
+                            rounded_cylinder(
+                                radius = [head_r / 2, head_r / 6], 
+                                h = head_r * 1.25, 
+                                round_r = 4
+                            );    
+
+            color("black") 
+                translate([0, -head_r * 1.6, 0]) 
+                    rotate([15, 0, 0]) 
+                        scale([1.25, 1, 1]) 
+                            sphere(head_r / 7);    
+        }
+        
+        module eye() {
+            translate([head_r / 2, -head_r / 1.75, head_r / 3]) 
+                rotate([-20, 5, 30]) 
+                    scale([1.2, 0.5, 1]) union() {
+                        color("Goldenrod") 
+                            sphere(head_r / 3);
+
+                         color("white") 
+                             translate([0, 0, -head_r / 15]) 
+                                 rotate([-25, -10, 0]) 
+                                     scale([1.1, 1.25, 1.2]) 
+                                         sphere(head_r / 3.5);
+                     
+                        color("black") 
+                            translate([-head_r / 15, -head_r / 4, -head_r / 12]) 
+                                sphere(head_r / 7);
+                }    
+        }
+        
+        module eyes() {
+            eye();
+            mirror([1, 0, 0]) 
+                eye();
+        }
+        
+        module eyebrow() {
+            color("black") 
+                translate([head_r / 2.5, -head_r / 2.5, head_r / 3]) 
+                    rotate([60, 15, 30]) 
+                        linear_extrude(head_r / 2, center = true) scale([1.5, 1, 1]) 
+                            arc(radius = head_r / 3, angle = 120, width = head_r / 20);
+            
+        }
+        
+        module eyebrows() {
+            eyebrow();
+            mirror([1, 0, 0]) eyebrow();
+        }
+        
+        shape_pts = shape_glued2circles(head_r / 2, head_r * 2.5, tangent_angle = 35);
+
+        module ear() {
+            color("Maroon") 
+                rotate([-15, 0, -10]) 
+                    translate([-head_r / 2.75, head_r / 15, -head_r / 2.75]) 
+                        rotate([0, -60, 0]) 
+                            scale([1.25, 1, 1]) intersection() {
+                                translate([head_r, 0, 0]) 
+                                    linear_extrude(head_r) 
+                                        polygon(shape_pts); 
+
+                                difference() {
+                                    sphere(head_r);
+                                    sphere(head_r - head_r / 10);
+                                }
+                            }    
+        }   
+
+        module ears() {
+            ear();
+            mirror([1, 0, 0]) ear();
+        }    
+
+        head_nose();
+        eyes();
+        eyebrows();
+        ears();
+
+    }
+
+
+    module foot() {
+        translate([head_r, -head_r / 11, 0]) union() {
+            color("PapayaWhip") ellipse_extrude(head_r / 3) polygon(
+                shape_ellipse([head_r / 3, head_r / 2])
+            );
+            
+            color("Maroon")  linear_extrude(head_r) circle(head_r / 8);
+            
+            color("Goldenrod") translate([head_r / 45, 0, head_r / 2]) rotate([0, -15, 0]) rounded_cylinder(
+                radius = [head_r / 5, head_r / 3.5], 
+                h = head_r * 1.25, 
+                round_r = 2
+            );            
+        }    
+    }
+
+
+    module feet() {
+        foot();
+        mirror([1, 0, 0]) foot();
+    }
+
+    module body_feet() {
+        translate([0, -head_r / 5, -head_r * 1.65]) 
+            feet();
+
+        union() {
+            color("Goldenrod") scale([1, 1.25, 1]) difference() {
+                sphere(head_r);
+                
+                translate([-head_r, head_r / 6, -head_r]) 
+                    cube(head_r * 2);
+            }
+        }
+    }
+
+    module front() {
+        body_feet();
+
+        // neck
+        rotate([60, 0, 0]) 
+            union() {
+                color("Goldenrod") 
+                    linear_extrude(head_r * 2) 
+                        circle(head_r / 4);
+                
+                color("green") 
+                    translate([0, 0, head_r * 1.1]) 
+                        rotate([-10, 0, 0]) 
+                            rotate_extrude() 
+                                translate([head_r / 4, 0, 0]) 
+                                    circle(head_r / 10);
+            }
+    }
+    
+        
+    
+    translate([0, -head_r * 1.75 , head_r * 1.3]) 
+        head();
+        
+    difference() {
+        front();
+        
+        translate([0, head_r * 0.209, 0]) rotate([90, 0, 0]) latch_concave(latch_r1, latch_r2, latch_h, latch_spacing, $fn = 36);    
+    }
+}
+
+if(part == "FRONT") {
+    dog_front(head_radius, latch_r1, latch_r2, latch_h, latch_spacing);
+} else if(part == "SPRING") {
+    spring_dog_spring(head_radius, spring_levels, line_thickness, line_distance, latch_r1, latch_r2, latch_h, latch_spacing);
+
+} else if(part == "BACK") {
+    dog_back(head_radius, latch_r1, latch_r2, latch_h);
+}
+else {
+    dog_front(head_radius, latch_r1, latch_r2, latch_h, latch_spacing);
+    translate([0, spring_levels * (line_thickness + line_distance) + latch_h + latch_spacing, 0]) {
+        rotate([90, 0, 0]) spring_dog_spring(head_radius, spring_levels, line_thickness, line_distance, latch_r1, latch_r2, latch_h, latch_spacing);
+            
+        translate([0, 3.25, 0]) dog_back(head_radius, latch_r1, latch_r2, latch_h);
+    }
+}
+
+