Chap. 11.] CONSTRUCTION OP MACHINES. 235
clination is greater near the centre than at the end, andvaries regularly. Dove-tail the flights into the arm, ob-serving to put the side that is to drive the meal, to theline of inclination. The bottoms of them should not ex-tend past the middle line, the ends being all rounded anddressed off at the back side, to make the point sharp,leaving the driving side quite straight, like the flight r.(See them complete in the end ca.) The sweepersshould be 5 or 6 inches long, screwed on behind theflights, at the back side of the arms, one at each end ofthe arm, and one at the part that passes over the hop-per : their use is described in Art. 88.
The upright shaft should be 4 by 4 inches, and maderound for about 41 feet at the lower end, to pass lightlythrough the centre of the arm. To keep the arm steady,there is a stay-iron 15 inches high, its legs \ inch by £,to stride 2 feet. The ring at the top should fit the shaftneatly, and be smooth and rounded inside, that it mayslide easily up and down; by this the arm hangs to therope that passes over a pulley at the top of the shaft, 8inches diameter, with a deep groove for the rope or cordto run in. Make the leading arm 6 by 1| inches in themiddle, 2 by 1 inch at the end, and 8 feet long. Thisarm must be braced to the cog-wheel above, to keep itfrom splitting the shaft by an extra stress.
The weight of the balance w, must be so nearly equalto the weight of the arm, that when it is raised to thetop it will descend quietly.
In the bottom of the upright shaft is the step-gndgeon(fig. 15,) which passes through the square plate 4 by 4inches (fig. 14;) on this plate the arm rests, before theflights touch the floor. The ring on the lower end ofthe shaft is less than the shaft, that it may pass throughthe arm : this gudgeon comes out every time the shaft istaken out of the arm.
If the machine is to attend but one bolting-hopper, itneed not be above 12 or 13 feet long. Set the uprightshaft close to the hopper, and the flights all gather asthe end c b, fig. 13. But, if it is to attend for the grind-ing of two pair of stones, and two hoppers, make^it 15