In order to perform this doubling operation in an efficient manner for the production of thread, it is usual to employ two machines. The first of these is shown in the illustration, and is termed the quick traverse winding machine. Here the cops from the mule, or the bobbins from the ring frame, are fitted in a suitable creel, as shown clearly at the front and lower part of our illustration. Each thread of yarn is conducted over a flannel-covered board which cleans the yarn and keeps it tight. Then each thread passes through the eye of a small detector wire which is held up by the thread and forms part of an automatic stop motion which stops the rotation of any particular bobbin or "cheese" when an end or thread belonging to that "cheese" fails or breaks, leaving the needles or detector wires. All the threads--from two to six in number--belonging to one "cheese" are combined to form one loose rope or thicker thread. Image: FIG. 36.--Quick traverse winding frame. It ought to be explained that the term cheese is applied to the kind of bobbin of yarn which is formed upon this particular machine, one or two being placed as shown on the frame work. =Doubling Machine.=--The machine just described does not put any twist into the thread, although twisting is a process which is absolutely indispensable for the proper combination of the several single threads so as to produce a strong doubled thread. The twisting operation is therefore performed on the machine illustrated in Fig. 37, and termed the "Ring doubling machine." In the creel of this machine are placed the cheeses formed on the winding machine, and the threads are conducted downward and usually under a glass rod in trough containing water, as the addition of water helps to solidify the single threads better into one doubled thread. From the water trough the threads are conducted between a pair of revolving brass rollers which draw the threads from the cheeses and pass them forward to the front of the machine. Here each doubled thread extends downwards and passes through a "traveller" upon the bobbin. This machine is a modification of the ring spinning frame previously described and therefore does not call for detailed treatment at our hands. The two machines are practically identical in principle, the chief difference being that in the doubler there are no drawing rollers, as the cotton is not attenuated in any degree at this stage. Other differences consist in having larger "travellers" and "rings" and "spindles," and in a different kind of bobbin being formed. Image: FIG. 37.--Ring doubling machine. At the doubling mill these threads are submitted to finishing processes, by which they may be polished and cleared and finally wound upon small bobbins or spools ready for the market, as seen in Fig. 2.