Worn pivots and the best bearings for wheels
How a journal wears its hole, and the best ways to seat a pivot
The drawings study how a wheel's pivot (polo) wears the hole (buso) that carries it: the pivot a has worn its hole both downward, by the wheel's weight, and sideways, by the motion toward b along the line of its counterweight. Leonardo adds that if pivot and hole are tempered they wear each other equally, and records that Giulio reported seeing a wheel in Germany worn away by its pivot m. Further figures show what Leonardo calls the best ways to seat a pivot, both for one that makes complete turns and for one that does not, illustrated with calipers, wheels in frames, and grouped rollers. Parts are lettered a, b, c and m.
On this page
A pivot wears its hole both down and sideways
The pivot a has worn its hole downward, by the weight of the wheel, and crosswise, because of the motion this pivot makes toward b, that is along the line of its counterweight. If the pivot and the hole are tempered, they wear one another away equally.
Giulio's report of a wheel worn in Germany
Leonardo notes a second-hand observation: Giulio says that in Germany he saw one of these wheels worn away by the pivot m.
The best way to seat a pivot
If you want the pivot always to make its complete turns, this is the best way that can be done. And to receive a pivot upon itself that does not make a complete turn, this is likewise the best that can be done.