diff --git a/src/components/ViewerControls.tsx b/src/components/ViewerControls.tsx
index bc8b3ff..741304d 100644
--- a/src/components/ViewerControls.tsx
+++ b/src/components/ViewerControls.tsx
@@ -107,6 +107,30 @@ export function ViewerControls() {
         <span className="font-mono text-xs">Grid</span>
       </Button>
 
+      {/* Grid calibration: click a face on the piece to anchor the grid there */}
+      <Button
+        variant={gridCalibMode ? 'default' : 'outline'}
+        size="sm"
+        className="gap-2 h-9"
+        disabled={!activeModelId}
+        onClick={() => {
+          const next = !gridCalibMode;
+          setGridCalibMode(next);
+          if (next) {
+            setGridAutoFollow(false);
+            toast.info('Calibrar Grid: clique numa face da peça');
+          } else {
+            toast.dismiss();
+          }
+        }}
+        title="Posiciona o grid na altura de uma face da peça"
+      >
+        <LayoutGrid className="h-3.5 w-3.5" />
+        <span className="font-mono text-xs">
+          {gridCalibMode ? 'Clique na face…' : 'Calibrar Grid'}
+        </span>
+      </Button>
+
       {/* Scale presets */}
       <ScaleSelector />