So far we have mentioned only plain looms, or those limited to the capacity of eight or twelve pick cams. Before we consider any of the varied constructions relating to elastic webs it will be well to speak of fancy looms. There are different types, adapted to a wide range of fancy effects, but the fancy loom most generally used is what is known as the chain head, an example of which is shown at Fig. 1. Such looms are usually of 18 and 24 harness capacity, and are operated by a figure chain of the length required to produce the desired figure. Chains are made up of a series of bars, one bar operating with each pick of the loom and having on it space for a roller or sinker for each harness to be operated.
Wherever a roller is placed on the bar, the corresponding harness will be raised, and wherever a sinker is used, the corresponding harness will be dropped. A series of rollers following each other will hold the harness up, and likewise a series of sinkers following each other will keep the harness down, thus maintaining at all times an open shed.
The Shedding Operation
The shedding operation is very simple. In the fancy head there are two cylinders, each of which has gear teeth running the entire length. These cylinders operate continuously in opposite directions. The teeth of the cylinders do not go around the entire circumference as will be noticed on the upper cylinder shown in Fig. 1, but there is a blank space provided so as to allow for the engaging of the gear wheels brought into position at the right time as the cylinders revolve.
Between the two cylinders are vibrator gears, one for each harness, and to these gears are attached arms which are connected with the different harnesses. These vibrator gears can be thrown into position by the chain rollers or sinkers, so as to come in contact with the teeth of either the upper or lower cylinder, and are so timed that they take their position at the moment when the blank part of the cylinder presents itself. A vibrator gear engaging the upper cylinder is turned so as to lift the harness connected with it, while a vibrator gear engaging the lower cylinder drops that particular harness. The harnesses stay in their relative positions until the chain calls for another change.
Both cylinders and engaging gears are made of hard chilled steel, so that wear and tear by hammering at the time of engagement are reduced to a minimum. To further soften the engagement, the speed of the cylinder is controlled by elliptical driving gears, which reduce the speed of travel just at the moment when the engagement takes place.
The timing of the various movements of the head is so well controlled that there is little risk of any part failing to maintain proper relationship with the other parts. But in the event of any accident or breakage occurring which interferes with the free motion of the head, such strain is taken care of by a soft pointed set screw on the head driving shaft, which shears off and so prevents further serious damage.
The capacity of the head is such that by careful arrangement of figures and repeats it is quite possible to make several simple designs to run side by side in the same harnesses and this is often done. Of this we may write more later.
