It is assumed, for the purposes of this description, that the modern style of shafting, increasing in diameter by the ½ inch, is used, and that all pulleys and belts are in place. We will take a line composed of sizes ranging between 3 15/16 and 2 7/16 inches. This gives us four sizes, 3 15/16, 3 7/16, 2 15/16 and 2 7/16 inches in the line.

We will first consider the plumb-bob. The accompanying sketch, Fig. 47, illustrates a good one.

The ball is 1½ inches diameter, and the large end of the tapered stem ½ inch in diameter, turned parallel for a short distance at the lower end. The two thin sheet-steel disks, 1 and 2 inches in diameter, are drilled to fit snugly when pushed on to the ½-inch part of the stem, and stay there until pulled off. These disks are turned true. This arrangement of plumb-bob and disks enables us to deal with five sizes on one line, and there are not many lines that contain more.

Now having our plumb-bob ready, we will stretch the line. The stretchers should be set horizontally by nailing a strip of wood, say 1 à 1½ à 12 inches, with a piece at each end to form a space between it and the wall, or place of location in line with the edge of the shaft, as in Fig. 48. The top of this stretcher should be low enough to clear the largest pulley, and high enough to clear the hat of your tallest man. You would perhaps find it convenient to go between the spokes of a large pulley.

Now having located your stretcher, find approximately the position of your line, and drive a nail a foot or more below it in a vertical line, and another nail anywhere for convenient winding. The advantage of this plan is that the line can be easily adjusted as it merely passes over the stretcher, and is free to respond to movement either way; then when the final adjustment is made, and is ready for its final stretch, it is only necessary to pinch the line to the nail with one hand, while the other is at liberty to unwind, stretch and rewind the line without fear of its shifting.

The line being adjusted over the stretchers, we will now proceed to set it. Begin at the 2 7/16-inch end, by throwing your plumb line over the shaft and setting your line at that end, right with the center point of your bob. Having done so, go to the other or 3 15/16 end of your line, and set the line so that the edge of the ball of your bob just touches it. Now go back to the 2 7/16 end and see that the necessary adjustment did not alter it. Having proved this, give your line the final stretch and try if it is right at both ends. You now have a center line (though the edge instead of the center of the shaft is used) that may remain up for days if necessary without fear of disturbance.

It is best to go over the whole line first, before disturbing anything; so starting at the first hanger at the 2 7/16-inch end, throw your plumb line over the shaft, and record on the floor in chalk beneath it whether it is O. K. or wants to go either way, and how much; then go to the next hanger, and so on to the end. A short study of the conditions enables one to correct the faults, with a knowledge of the requirements, and consequently in the least time and with the least trouble.

Now suppose we start at the 2 7/16-inch end to inspect the line, we use the center point of the bob on the line so long as we are testing 2 7/16 inches.

When we get to the 2 15/16-inch part, which is ½ inch larger, we use the half diameter of the stem, the edge of which should just touch the line.

When we come to the 3 7/16-inch part, 1 inch larger than 2 7/16, we use the 1-inch disk, slip it on to the stem, and when it just touches the line with its edge it is O. K.

The 3 15/16-inch, being 1½ inches larger than the 2 7/16-inch, will be right when the ball of the bob is in light contact with the line.

The 2-inch disk would be suitable for the next size, and other disks or modifications of the bob proper might be made to suit circumstances.

Now having straightened the line, the next process is to level it. As in some cases your pulleys will be too close to place your level where you want, make a light iron frame as per Fig. 49, making the suspending members of sufficient length to admit of your reading the level conveniently when standing on the floor. Hang your frame on the shaft, and put your level on the straight-edge below; in this way travel along the shaft, placing your frame where convenient. Be sure that one end of your frame does not rest on a shaft of different diameter, a key, keyseat, or anything to distort the reading.

Never be content with trying your level, especially an adjusting level, one way; always reverse it and try again; for if it is out of truth at the start, you might want to go through the roof or down cellar at the finish. Get into a habit of reversing your level, and so prove your work as you proceed.

V