Mechanics of wheels: friction, axles and gear teeth
An outline of a science of motion and weight, with rules for pinions and toothed wheels
This densely written sheet lays out Leonardo's programme for a science of mechanics and applies it to wheels and gearing. He plans to treat, in order, motion, weight, force and percussion, then wheels that turn one way or reciprocate, screws, levers, balances, mills and toothed gears. Practical notes analyse how friction at the axles ('poli') resists turning, how a loaded cart burdens its axle, and how the teeth of pinion and wheel should engage — the driving tooth always kept in line with the two axles. Discs, pulley blocks with counterweights (16-16-88), a toothed wheel and pinion, and a masked dredge-like form are drawn beside the text.
On this page
Friction at the axles resists the wheel's turning
The frictions made by the axles ('poli') of the wheels against the hollows that receive them are the cause of making their turning difficult. It is as much labour to move the road under the weight as the weight over the road.
A plan for the science of motion, weight, force, percussion
Speak first of motion, then of weight (born of motion), then of the force born of weight and motion, then of percussion born of weight, motion and force. Then treat wheels that turn one way and wheels that go and return, the screw, levers and balances, mills and instruments for moving and throwing, and finally the teeth — beginning with the axles and what receives them.
A loaded cart burdens its axle
If a cart is light and set on a very perfect plane, the mover feels little labour; but load it heavily and its movement becomes difficult. The cause is the axle ('polo') that receives such a load and passes it to its point of contact.
Pinion and wheel: how the teeth engage
Make a general rule for giving a pinion that will move every wheel, and a wheel that will turn every pinion, from one tooth up until the wheels are equal. The tip of the driving tooth must always lie in line with the two axles of its two wheels, so that as one tooth leaves, the other touches the whole side of its tooth.
The smaller the pinion, the deeper the wheel's teeth bite
The smaller the pinion ('rocchetto') is relative to its wheel, the more deeply it will be penetrated by the teeth of the large wheel. The remark bears on how gears of unequal size mesh.