Add ender 3 secondary spool holder

models/spool_holder.scad

@@ -0,0 +1,36 @@
+// A second spool holder for ender 3. This replaces the back piece that tightens
+// onto the original spool holder.
+
+// TODO - On mine, it fits slightly loose when printed at 0.2 layer height.
+// tab_height might need increasing to fix.
+
+spool_width = 90;
+wall_thickness = 1.5;
+
+connector_inner = 15.5;
+tab_height = 4; // TODO - test increasing tab_height by 0.2?
+
+difference() {
+    union() {
+        cylinder(h=10, d=40);
+        cylinder(h=10 + spool_width, d=(2 * (connector_inner + wall_thickness)));
+        translate([0, 0, (10 + spool_width)]) {
+            cylinder(h=3, d1=(2 * (connector_inner + wall_thickness)), d2=((2 * (connector_inner + wall_thickness)) + 6));
+        }
+        for(i = [0 : 60 : 300]) {
+            rotate([0, 0, i]) {
+                translate([19, 0, 0]) {
+                    cylinder(h=10, r=3);
+                }
+            }
+        }
+    }
+    translate([0, 0, -1]) {
+        cylinder(h=spool_width + 15, d=(2 * connector_inner));
+    }
+}
+for(i = [-1, 1]) {
+    translate([connector_inner * i, 0, tab_height]) {
+        cylinder(h=3, r=2.5);
+    }
+}