Working model after Leonardo da Vinci, Madrid Ms. I (BNM), fol. 26r
The screw jack's anti-friction mechanism is visible through the Plexiglas panel. The crank-driven worm screw meshes with the crown wheel, raising and lowering the vertical screw slowly but effortlessly even when a heavy load is attached. To reduce friction, Leonardo has placed spheres between the crown wheel and the supporting platform.
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