A mechanical device includes a long, narrow element made of a rigid, elastic material. A rigid frame is configured to anchor at least one end of the element, which is attached to the frame, and to define a gap running longitudinally along the element between the beam and the frame, so that the element is free to move within the gap. A solid filler material, different from the rigid, elastic material, fills at least a part of the gap between the element and the frame so as to permit a first mode of movement of the element within the gap while inhibiting a different, second mode of movement.