From a769d51d9f9d328a6b39a7a3c5def0c99a706089 Mon Sep 17 00:00:00 2001
From: "gpt-engineer-app[bot]"
 <159125892+gpt-engineer-app[bot]@users.noreply.github.com>
Date: Sun, 24 May 2026 20:50:18 +0000
Subject: [PATCH] Changes

Co-authored-by: Reifonas <211114984+Reifonas@users.noreply.github.com>
---
 src/components/three/ModelViewer.tsx | 29 ++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/src/components/three/ModelViewer.tsx b/src/components/three/ModelViewer.tsx
index 14cbf51..9fa1ffa 100644
--- a/src/components/three/ModelViewer.tsx
+++ b/src/components/three/ModelViewer.tsx
@@ -1035,34 +1035,39 @@ function GridLayer() {
   );
 }
 
-/** Continuously aligns the grid Y to the bottom of all visible models so the
- *  piece always looks like it is sitting on the grid — including after
- *  calibration, fine-tuning, repositioning or scale changes. */
+/** Continuously aligns the grid Y to the bottom of all registered model
+ *  groups (not the entire scene), so the piece always sits on the grid —
+ *  including after calibration, fine-tuning or repositioning. */
 function GridAutoFollower() {
-  const { scene } = useThree();
   const lastY = useRef<number>(Number.NaN);
   const acc = useRef(0);
   useFrame((_, dt) => {
     const auto = useModelStore.getState().gridAutoFollow;
     if (!auto) return;
-    // Throttle to ~10 Hz to keep this cheap.
     acc.current += dt;
     if (acc.current < 0.1) return;
     acc.current = 0;
+    const groups = getAllModelLocalGroups();
+    if (groups.length === 0) return;
     const box = new THREE.Box3();
     let has = false;
-    scene.traverse((obj) => {
-      if (obj instanceof THREE.Mesh && obj.geometry) {
+    const tmp = new THREE.Box3();
+    for (const g of groups) {
+      g.updateWorldMatrix(true, true);
+      tmp.makeEmpty();
+      g.traverse((obj) => {
+        if (!(obj instanceof THREE.Mesh) || !obj.geometry) return;
         if (obj.geometry instanceof THREE.SphereGeometry) return;
         if (obj.geometry instanceof THREE.RingGeometry) return;
         if (obj.userData.__edgeLine) return;
         const b = new THREE.Box3().setFromObject(obj);
-        if (isFinite(b.min.y)) {
-          if (!has) { box.copy(b); has = true; }
-          else box.union(b);
-        }
+        if (isFinite(b.min.y)) tmp.union(b);
+      });
+      if (!tmp.isEmpty() && isFinite(tmp.min.y)) {
+        if (!has) { box.copy(tmp); has = true; }
+        else box.union(tmp);
       }
-    });
+    }
     if (!has) return;
     const target = box.min.y - 0.005;
     if (!Number.isFinite(lastY.current) || Math.abs(target - lastY.current) > 1e-4) {