Fig. 2587.
In stretching and adjusting this line, however, we have the following considerations:—It must clear the largest pulley hub on the line of shafting, those pulleys having set-screws being moved to allow it to pass. If the whole line of shafting is parallel in diameter, we set the line equidistant from the shafting at each end. If one end of the shafting is of larger diameter, we set the line farther from the surface of the shafting, at the small end, to an amount equal to one-half of the difference in the two diameters; and since the line is sufficiently far from the shafting to clear the largest hub thereon, it makes, so far as stretching the line is concerned, no difference of what diameter the middle sections of shafting may be. The line should, however, be set true as indicated by a spirit-level.
We may now proceed to erect the targets as follows: The planed edge a in [Fig. 2585] is brought true with the stretched line, and is adjusted so that the plumb-line b in [Fig. 2586] will stand true with the line or mark b. When so adjusted, the target is nailed to the post carrying the shafting hanger. In performing this nailing, two nails may be slightly inserted so as to sustain the target, and the adjustment being made by tapping the target with the hammer, the nails may be driven home, the operator taking care that driving the nails does not alter the adjustment.
Fig. 2588.
In [Fig. 2588] a a represents the line of shafting, b, b two of the hanger posts, and c, c two of the adjusted targets.
Fig. 2589.