diff --git a/follow_focus.py b/follow_focus.py
index 60cf306..d36c06b 100644
--- a/follow_focus.py
+++ b/follow_focus.py
@@ -61,7 +61,9 @@ base = base.edges('|Z and <X').fillet(outer_fillets)
 base = base.edges('|Z').edges('<<Y[-2]').fillet(5)
 
 # Shell
+copy = base.faces('>>Z[0]').workplane().center(0, -offset-loop_thickness).polarLine(2*stepper_motor_size, slant_degree).vLine(-2*stepper_motor_size).hLine(-2*stepper_motor_size).close().cutThruAll()
 base = base.faces('+Z').shell(-1.6)
+base = base.add(copy)
 
 # Stepper motor mount points
 stepper_hole_width=31.0