_Bobbin Building._—The outstanding advantage of this machine is the efficient manner in which the bobbin is built, and in this process several factors have to be considered. The thread guide G has a regular up-and-down motion for the traverse, this upward and downward sweep being brought about by the heart-shaped cam C which, by its revolving action, causes the whole stage P to rise and fall, thus giving a similar motion to the thread guide. Partaking in this traverse is the spiral S with the wheel W, which has a ribbed surface to preserve contact with the yarn level. The wheel W has a finger V attached, which in turn works into the spiral of rod S, and whenever the yarn rises to a certain level on the bobbin, it comes into frictional contact with the ribbed wheel which receives a turn sufficient to cause the wheel and guide to rise higher on the spiral and with it the thread guide also assumes a more elevated position. In this way the wheel W and the thread guide G travel from the lower end of the spiral S to the other upper end during the operation of filling a single bobbin. Up to this stage the action may be detailed thus: the thread guide receives its traverse over a certain distance of the bobbin by the action of the heart-shaped cam C, this being denoted by the dotted positions C1 for cam, K1 for stud, P1 for the stage, G1 for the guide, and this motion proceeds regularly during the winding operation. There is next the gradual rising of the guide on the spiral rod caused by the turning of the bobbin B, the high part of the bobbin B having friction with the ribbed wheel W causing it to rise gradually on the spiral.
_The Differential._—The final element in successful bobbin building is the differential and the means of securing this are ingenious in the highest degree. The driving wheel DW with its rough leather rim works on the disc FW and causes it to rotate, but the speed of rotation must vary according as the upper or the lower part of the bobbin is being filled. When the yarn is passing on to the bare part of the bobbin as it does at the upper sweep of the traverse, one revolution coils a very much smaller length of thread than it does at its lowest position when the bobbin is full. The rate of winding varies differentially according to the intermediate positions of the thread, in the upward sweep of the traverse the speed of the bobbin accelerates as the bare part is approached, whilst on the downward sweep the speed of the bobbin decreases, reaching its slowest when the full part of the bobbin is attained. This differential is produced by a side-to-side movement of the driving wheel DW over the rim of the disc FW, from the outer rim and slowly towards the inner rim and _vice versâ_. When the wheel is driving at its extreme position on the outer rim the bobbin is running at its slowest, because the driving wheel has a longer distance to traverse in order to effect one bobbin revolution. When the driving wheel is acting at its furthest position inwards the bobbin is at its highest speed, and this takes place with graduated differences in the intermediate stages of the process.