LEONARDO DA VINCI - Systems to reduce friction on rotating axles - Adjustable bearings
Madrid Ms. I (BNM), fol. 100v (detail)
The two devices - one using a wedge (top), the other a screw (bottom) - are designed to keep a constant grip on the axle as the support wears down. Leonardo also recommends making the support frame out of "mirror metal, that is, 3 parts of copper and 7 of tin, melted together," a highly friction-resistant alloy.