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.
Fig. 49.