Wear of gear pivots, steel bearings, and tooth ratios
Rules for sizing and hardening pivots so wheels and pinions last
A page of paired notes and gear sketches on how to keep wheels and lantern-pinions from wearing out. Leonardo argues that heavy or fast wheels need long pivots so the load spreads over more contact, that soft-on-soft and hard-on-soft both wear away, so pivots and their holes should both be tempered steel, and that a lantern-pinion's spindles last longest when the wheel's teeth touch them along their whole length. He warns that a wheel turning on a fixed pivot enlarges its own central hole and is spoiled, and states the proportional rule that a pinion with one-tenth the teeth of its wheel wears out ten times faster. The many small drawings show paddle-wheels, drums, gear pairs, lantern-pinions and a toothed ring.
On this page
Long pivots for heavy or fast wheels
When the weight is large, or light but fast-moving, the pivots should be long, so that the load discharges itself over much contact. When the pivots are short and the weight heavy or fast, they wear away both themselves and the hole that supports them.
Hard on hard: tempered-steel pivots and holes
Because soft with soft and hard with soft wear one another away, it is necessary to make hard with hard. So make the pivots of the wheels of tempered steel, and likewise the holes that receive them also of tempered steel.
Contact length and tooth ratio govern the rate of wear
A lantern-pinion's spindles last if the wheel's teeth touch them along their whole length, but wear fast where contact is small. A wheel turning on a fixed pivot enlarges its own central hole. And if the wheel's teeth are ten times those of the pinion, the pinion wears out ten times faster than the wheel.