The ritenaculo: a ratchet wheel and its serving pawl
On power and resistance; the Florentine catch that stops a moved load from slipping back
Headed "On power and resistance," this page describes an engineers' instrument the Florentines call the ritenaculo: an orthogonally toothed circle whose sole job is to keep a moved load from slipping or turning back, a great security for movers of weights (text 3). The pawl resting on its teeth is called the servidore because it obeys and serves the wheel; its line must form a right angle with the tooth's line, while the tooth's line is directed to the wheel's centre. Leonardo prescribes making the pawl level so it always bears toward its seat, with the tooth beneath it tangent to it, as the first degree of the instrument's goodness. The drawing shows a ratchet wheel with a rope-wound axle, a hanging weight, and the pawl marked with the letters n, m, a.
On this page
The ritenaculo and its servidore (pawl)
The instrument the Florentines call ritenaculo is an orthogonally toothed circle that only keeps a moved thing from slipping or turning back, a great security for movers of weights. The support resting on its teeth is called servidore because it obeys and serves the wheel.
Right-angle geometry of pawl and tooth
The line of the servidore must form a right angle with the line of the wheel's tooth, and the tooth's line must be directed to the centre of its wheel. The pawl is made level so it always weighs toward where it rests, and the tooth beneath it must be entirely tangent with it.