Most of the frame up to the Y sleds is done

stock_parts.scad

@@ -0,0 +1,23 @@
+stock_color = "lightgray";
+
+bushing_od = 12;
+bushing_id = 8;
+bushing_len = 8;
+
+module bushing() {
+  colorize(stock_color) {
+    difference() {
+      cylinder(d = bushing_od, h = bushing_len);
+      translate([0,0,-1])
+	cylinder(d = bushing_id, h = bushing_len + 2);
+    }
+  }
+}
+
+module colorize(colorname) {
+  if (use_colors) {
+    color(colorname) union() { children(); }
+  } else {
+    children();
+  }
+}