Crank handles converting rotary motion into saw-like reciprocation
The 'mezzano' intermediary and how its angle governs the effort
The page studies crank handles on wheels whose circular motion is turned, through an intermediate link the engineers call the 'mezzano', into a straight back-and-forth motion 'in the manner of a saw'. Leonardo argues that a longer intermediary and a more acute angle between it and the driven rod make the motion easier, while a larger angle makes it harder for the mover. A lower series of crank-and-disc mechanisms shows handles a, b, c, d that can each be worked by up to four pullers, with notes on how many can pull at once and the best moment to throw one's full force forward.
On this page
Wheel handles giving a saw-like straight motion
A crank on a wheel drives, through an intermediate member, a rod that goes and returns like a saw; the longer this intermediary, the easier the motion. The member a n is what the engineers call the 'mezzano', set properly midway between the driving handle and the thing it moves.
Angle of the intermediary sets the effort
The larger the angle formed where the intermediary joins the rod it moves, the more difficult the motion becomes for its mover; the more acute the angle, the easier. The acute, favourable case is the one made here above by the intermediary b m with the rod S m.
Handles worked by four pullers
Each handle a, b, c, d can be pulled by four pullers set at equal distances, as shown at handle d. But in a and b only one of the four can pull at a time, while in c and d two pull at once, so they are not equally strong; a man should first draw back as far as he can, begin to return a little, then at once throw his whole force forward.