Not only is it necessary to provide special apparatus for twisting the cotton at the bobbin and fly frames, but also very complicated and highly ingenious mechanism for winding the attenuated cotton in suitable form upon the bobbins. Indeed it is with this very mechanism that some of the most difficult problems of cotton spinning machinery are associated.
Although the cotton at this stage is strengthened by twist, yet it is extremely inadvisable and practically inadmissible to insert more than from 1 to about 4 twists per inch at any of these machines, so that at the best the rovings are still very weak.
If too much twist were inserted at any stage, the drawing rollers of the immediately succeeding machine could not carry on the attenuating process satisfactorily.
This winding problem was so difficult that it absolutely baffled the ingenuity of Arkwright and his contemporaries and immediate successors, and it was not until about 1825 that the difficulties were solved by the invention of the differential winding motion by Mr. Holdsworth, a well-known Manchester spinner, whose successors are still eminent master cotton spinners.
This winding motion is still more extensively used than any other, although it may be said that quite recently several new motions have been more or less adopted, whose design is to displace Holdsworth's motion by performing the same work in a rather more satisfactory manner.
In these pages no attempt whatever will be made to give a technical explanation of the mechanism of the winding motion. It may be said that it was a special application of the Sun and Planet motion originally utilised by Watt in his Steam Engine, for obtaining a rotary motion of his fly-wheel.
Sufficient be it to say that this "Differential Motion," acting in conjunction with what are termed "Cone drums," imparts a varying motion to the bobbins upon which the cotton is wound, in such a manner that the rate of winding is kept practically constant throughout the formation of the bobbins of roving, although the diameters of the latter are constantly increasing.
The spindles and bobbins always rotate in the same direction, but while the revolutions per minute of the spindles are constant, so as to keep the twist uniform, those of the bobbins are always varying, in order to compensate for their increasing diameters or thicknesses of the bobbins. The delivery of cotton from the rollers is also constant and the mechanism required to operate them is exceedingly simple.
A vast number of details could easily be added respecting the operations performed by the bobbin and fly frames, but further treatment is deemed unnecessary in this story.