Screw-jacks, wedges, and driving oblique-pointed piles
Every screw or rack must pivot top and bottom; a pile's oblique point acts as a screw; where a wedge's tip ends up
On this folio (149r) Leonardo studies weight-raising mechanisms and the geometry of the wedge. A lever-and-screw hoisting device at the upper right is paired with notes that any screw or rack moving a load must be pivoted at both its foot and its head so it can follow every degree of the lever's circular motion. Lower drawings show a row of piles being driven into the ground by their oblique-cut points, which act like screws, and a wedge o m n whose slanted face is analysed to find where its tip finally rests within its own base.
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A screw or rack must pivot at both foot and head
Any screw or rack that raises a weight by a beam-lever must be pivoted below and above. If it is a screw, its nut sits on a pivot, and a second toothless nut carries and turns the screw's foot; a rack likewise runs in a mortise or channel. This lets the instrument follow every degree of the lever's circular motion.
Piles whose oblique point acts as a screw
This is a way of driving piles into the ground so that the very motion of driving makes them draw together. The cut of the point is oblique, so that as the pile sinks it performs the office of a screw. Below, a query asks on which side, s or f, the ground will remain harder.
Where a wedge's tip ends up within its base
If the wedge o m n is driven into a yielding material, at what part of its upper base will the entry-point of its tip lie? Being straight on one side and oblique on the other, its slanted face acts on the material as a screw acts on the obliquity of its nut. So the spot the tip first touched will, at full entry, be found at the middle of the wedge's base.