Screw hoist for raising a bell into its tower
With a tool for cutting a female screw and a double-rope lifting wheel
The sheet works out how to raise and seat a large bell at the top of a bell-tower, an ornate Gothic campanile drawn at the right with the bell hoisted inside it. Once the bell has reached its height, a female screw M is turned so the bell, held by n, climbs the last stretch along guide-beams to its place, a descending counterweight box doing the lifting. Two subsidiary devices are worked out beside it: an instrument that cuts the female thread (madrevite) of a wooden screw, and a wheel carrying two ropes wound in opposite directions so that one rises as the other falls.
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Screw hoist and counterweight for seating a bell
When the bell reaches its height, the hauling timbers are locked into two strong hooks, then the female screw M is turned and the bell, held fast by n, rides up the flanking beams to its place. Each time the counterweight box exceeds the bell by more than ten pounds it descends and draws the bell up, that ten-pound margin being held back by a rope and lowered little by little.
Instrument for cutting a female screw (madrevite)
In a block M a hole is bored as wide as the screw was before threading, and an iron two fingers wide and thin as a bowstring is nailed at a b to project half a finger into the hole. In a second block f r a helical channel is cut to the form of the screw; as the iron a b runs in this channel it advances, and the little blade c d hollows out the female thread.
Wheel with two counter-wound ropes
A wheel on whose axle two ropes are wound in opposite directions is offered as a way to do a job quickly. As one rope pays out and returns, the other is drawn up.
Gothic campanile receiving the bell
The tall tower at the right, with pinnacle, gabled belfry stage and buttressed shaft, is the bell-tower into which the bell is hoisted. It is drawn as the architectural setting for the lifting apparatus at the left.