In many cases the spindles at this stage are kept on revolving in order to put in any twist that may be lacking in any portion of the stretch.
Twisting being finished, the important operation of "backing off" commences.
It maybe at once explained that "backing off" means the reversing of the spindles; the uncoiling of a portion of the yarn from the spindles; and generally putting all the requisite apparatus into position ready for winding or coiling the attenuated and twisted rovings upon the spindles.
Here come now into action those most beautiful and ingenious applications of mechanical principles, the working out of which entailed so many years of arduous effort, and which rendered the mule practically self-acting and automatic.
By a most wonderful, intricate and clever combination of levers, wheels, pulleys and springs, aided by what is called a "friction clutch," the instant the spindles have ceased twisting the yarn, they are reversed in direction of revolution.
This reversal only occupies two or three seconds, and as the motion imparted to the spindles is very slow at this stage, the practical effect is, that a small portion of yarn is "uncoiled" from each spindle, sufficient to allow of two "guide wires" to assume proper and necessary positions for winding the attenuated threads upon the spindles.
These two wires are termed "faller wires," and while one is controlled by the cop-shaping mechanism and termed the "winding faller wire" the other simply keeps the threads in the requisite state of tension during "winding on" and is termed the "counter" or "tension faller wire." Both these wires can be seen in [Fig. 28]. During backing off, the "winding faller wire" has a descending motion, while the "counter faller" has an ascending motion, these being necessary for them to attain their proper positions for "winding on."
Fig. 28.—Mule showing action of faller wires.