The stamp of the flax-brake: five ways to gain power
Mechanics of the pounding lever; a man's shifting weight adds force to the blow
Folio 31 verso studies the blow of the stamp (pestone) of a flax-brake (gramola), a foot-operated pounding lever, worked out in text on the left and in lettered figures on the right. Leonardo grades five ways of driving it, from 'simple' to 'greatly increased' power, showing how a man who shifts his body weight from one lever to another can make a 200-pound stamp strike as if it weighed 401 pounds. He also proves, invoking 'the fifth of the ninth,' that a heavy man yields far less at the point of percussion than one would expect, and ranks the fifth mode - hanging on the lever's rope - as 'the prince of all.' The diagrams carry the labels a, b, n, m, o, p, d and figures of 100 to 400 pounds.
On this page
The stamp (pestone) of the flax-brake (gramola)
The page opens 'on the blow of the stamp of the flax-brake,' a foot-worked pounding lever. The operator drives the heavy stamp down against the brake while steadying himself on ropes overhead.
Adding the body's weight to the blow: 401 pounds
In the greatly increased mode the man weighs 201 pounds and the stamp 200. Setting all his weight on the foot of lever b lifts the stamp; shifting it to lever a adds his own weight to the blow, so it lands as 401 pounds, while he hangs from the ropes as he steps across.
Why 200 lb of man gives only 50 lb at the blow
Leonardo argues that a 200-pound man on a 100-pound stamp is left not with 100 but with 50 of effective power. He proves it by how far the bar a d bends to points a and b, citing 'the fifth of the ninth,' and concludes only 50 pounds reach the site of percussion.
Second and third modes: footwork about the pivot n-m
In the second mode one foot rests over the stamp's pivot at n and the other at m; loading foot m raises the stamp, loading the foot over n drops it to its blow. In the third mode the man straddles the pivot, raising the stamp with one foot and lowering it with the other.
Fourth and fifth modes; the fifth is 'the prince of all'
The fourth mode resembles the first but is better, since it does not lose the force the bar wastes in bending. The fifth, called the prince of all, uses a great lever: the man hangs on its rope, then shifts rope and footing to throw his whole weight in the stamp's favor.
The lever rope must be thick to bear the hands
A note on the fifth figure specifies that the rope of the lever must itself be thick, so that the hands leaning on it can add their weight. The points a, b flank the figure with the numbers 200 and 400.