diff --git a/src/kiri/core/widget.js b/src/kiri/core/widget.js
index 85b16879..f72115da 100644
--- a/src/kiri/core/widget.js
+++ b/src/kiri/core/widget.js
@@ -332,6 +332,10 @@ class Widget {
         moto.space.refresh();
     }
 
+    isSynth() {
+        return this.track.synth ?? false;
+    }
+
     isVisible() {
         return this.getMaterial().visible;
     }
diff --git a/src/kiri/mode/cam/client.js b/src/kiri/mode/cam/client.js
index 16459738..40adae9e 100644
--- a/src/kiri/mode/cam/client.js
+++ b/src/kiri/mode/cam/client.js
@@ -810,6 +810,7 @@ export function init() {
         clearPops();
         for (let group of Widget.Groups.list()) {
             let root = group[0];
+            if (root.tabs)
             for (let tab of Object.values(root.tabs)) {
                 let geo = tab.box.geometry.clone();
                 if (geo.index) geo = geo.toNonIndexed();
diff --git a/src/kiri/mode/cam/prepare.js b/src/kiri/mode/cam/prepare.js
index 1bc4c4b7..079cc378 100644
--- a/src/kiri/mode/cam/prepare.js
+++ b/src/kiri/mode/cam/prepare.js
@@ -26,7 +26,7 @@ export async function cam_prepare(widall, settings, update) {
     print.output = [];
 
     let point;
-    widgets.forEach((widget, index) => {
+    widgets.filter(w => !w.isSynth()).forEach((widget, index) => {
         point = prepEach(widget, settings, print, point, (progress, msg) => {
             update((index * weight + progress * weight) * 0.75, msg || "prepare");
         });
@@ -337,7 +337,7 @@ export function prepEach(widget, settings, print, firstPoint, update) {
         // 1. move to safe z of current point preserving angle
         // 2. move to safe z of new point preserving old angle
         // 3. move to safe z of new point with new angle
-        if (lop && lop !== currentOp && lastPoint) {
+        if (lop !== currentOp && lastPoint) {
             // compensate for applyWidgetMovement() applied to lastPoint
             let lpo = lastPoint.clone().move({ x: -wmx, y: -wmy, z: -zadd });
             camOut(lpo.clone().setZ(zsafe).setA(lastPoint.a), 0);