Form of gear teeth and wear of axle-pivots
Learn true tooth shape from worn mill wheels; why short pivots are better, and the use of oil
This all-text folio strings together short paragraphs on gearing: a wheel driving a smaller pinion needs longer teeth, and Leonardo advises studying worn mill-wheel teeth to learn the true shape necessity gives their flanks (text 1). He observes how the number and size of teeth govern the difference between notch-bottom and notch-mouth, insisting the teeth always keep the same figure. Turning to pivots (poli), he argues a pivot with less contact wears out sooner, and that ungreased pivots file their own holes; olive oil helps, but with dust and time it thickens and clogs the motion, as seen in clock counterweights where greasing makes ten pounds do the work of a hundred.
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Learn true tooth form from worn mill wheels
To find the true form of the flanks of gear teeth, go to the mills where long use has almost worn the teeth away and study what remains of the driving and driven tooth; there experience shows what shape necessity forces on their contacting flanks. A wheel driving a smaller pinion needs longer teeth.
Tooth number, notch depth and constant tooth figure
On a large wheel with many teeth there is little variation from notch-bottom to notch-mouth, but with few teeth the mouths vary greatly from their bottoms; smaller wheels show the greatest disparity. The spaces vary with wheel size, yet the teeth must always keep the same figure.
Wear of pivots and the use of oil
Of equally loaded pivots, the one with less contact wears itself and its support out soonest. Ungreased pivots file their holes, leaving filing-dust at their seats; olive oil helps, but dust and time thicken it and hinder motion. In clock counterweights, greasing the pivots and pinion teeth lets ten pounds do the work of a hundred.