diff --git a/src/woodshop/gui/viewport.py b/src/woodshop/gui/viewport.py
index ed3904a..5c6a518 100644
--- a/src/woodshop/gui/viewport.py
+++ b/src/woodshop/gui/viewport.py
@@ -7,7 +7,7 @@ from PySide6.QtWidgets import (QApplication, QHBoxLayout, QPushButton,
                                QVBoxLayout, QWidget)
 
 from ..scene import Scene
-from ..viewer import _PALETTE, _part_mesh, _quiet_vtk
+from ..viewer import _PALETTE, _add_feature_edges, _part_mesh, _quiet_vtk
 
 
 class Viewport(QWidget):
@@ -64,13 +64,16 @@ class Viewport(QWidget):
         labels, pts = [], []
         for i, part in enumerate(scene.parts):
             selected = part.id in selected_ids
+            mesh = _part_mesh(part)
             actor = self.plotter.add_mesh(
-                _part_mesh(part),
+                mesh,
                 color="#f5d76e" if selected else _PALETTE[i % len(_PALETTE)],
                 show_edges=not part.features, line_width=3 if selected else 1,
                 edge_color="black", reset_camera=False, pickable=True,
             )
             self._actor_to_pid[actor] = part.id
+            if part.features:
+                _add_feature_edges(self.plotter, mesh, selected)
             mid = [part.position_in[j] + part.axis_unit()[j] * part.length_in / 2 for j in range(3)]
             labels.append(part.name or part.id)
             pts.append(mid)
diff --git a/src/woodshop/viewer.py b/src/woodshop/viewer.py
index 1549959..08018c1 100644
--- a/src/woodshop/viewer.py
+++ b/src/woodshop/viewer.py
@@ -54,6 +54,20 @@ def _part_mesh(part: Part):
     return cube
 
 
+def _add_feature_edges(plotter, mesh, selected: bool) -> None:
+    """Overlay a tessellated solid's real edges (corners/holes/chamfers) so it
+    reads as crisply as a plain board, without the triangle-mesh noise."""
+    try:
+        edges = mesh.extract_feature_edges(
+            feature_angle=20, boundary_edges=True, feature_edges=True,
+            manifold_edges=False, non_manifold_edges=False)
+        if edges.n_points:
+            plotter.add_mesh(edges, color="yellow" if selected else "black",
+                             line_width=3 if selected else 2, reset_camera=False)
+    except Exception:
+        pass
+
+
 def _quiet_vtk() -> None:
     """Stop VTK from spamming warnings (esp. headless) through Python logging."""
     try:
@@ -71,14 +85,17 @@ def _render(plotter, scene: Scene) -> None:
     labels, label_pts = [], []
     for i, part in enumerate(scene.parts):
         edge = part.id == scene.selection
+        mesh = _part_mesh(part)
         plotter.add_mesh(
-            _part_mesh(part),
+            mesh,
             color="#f5d76e" if edge else _PALETTE[i % len(_PALETTE)],
-            show_edges=not part.features,   # triangle mesh would look noisy with edges
+            show_edges=not part.features,   # plain boxes: real quad edges
             line_width=3 if edge else 1,
             edge_color="black",
             smooth_shading=False,
         )
+        if part.features:                   # tessellated: overlay only the true edges
+            _add_feature_edges(plotter, mesh, edge)
         mid = [part.position_in[j] + part.axis_unit()[j] * part.length_in / 2 for j in range(3)]
         labels.append(part.name or part.id)
         label_pts.append(mid)