Instruments for shaping templates and a rasp lathe
Sagoma instruments, unequal wheels on one axis, and drawing a circle's arc
This sheet gathers workshop instruments alongside a geometry note. A 'sagoma' instrument, marked good, turns a template four arm-lengths long in one whole revolution and is meant to give and polish a true concavity using a template in place of a diameter; Leonardo observes that unequal wheels on the ends of one axis trace circles in the same proportion as the wheels. A lathe (fresa/tornio) passes a rod through a hole so that a rasp or file removes whatever thickness exceeds uniformity, the filings falling through two holes a b. In the margins a geometrical note gives, between the fronts of two converging lines, part of the circumferential line drawn about the point where they meet, with an arc a o b judged not very useful.
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Instrument for turning and polishing a template (sagoma)
Marked good, the instrument between a c turns a template of four arm-lengths in one whole revolution and serves to give and polish the true concavity with a template in place of a diameter. Unequal wheels set on the opposite ends of one axis describe circumferential lines in the same proportion as the wheels, the circles being greater the more nearly equal the wheels.
Lathe that files a rod to uniform thickness
A lathe passes a rod through a hole so that all the thickness exceeding the uniformity of the whole is consumed by a roughened rasp or file, the filings falling through the two holes a b.
Arc drawn about the point of two converging lines
In the space between the fronts of two converging lines, Leonardo gives part of the circumferential line made about the point where the concurrence of those lines directs itself, defining the arc appropriate to that centre.