Rack and Pinion Movement
The shuttles across the entire width of the loom are drawn to and fro by what is known as the rack and pinion movement. (See Fig. 2). This method has pretty generally superseded the old-time plan of rise and fall pegs. The rack runs back and forth in a slot grooved in the top of the lay bed, A, the entire length of the loom. To the rack is attached leather straps G, or heavily woven fabric straps, with which the rack B is pulled to and fro at each pick of the loom. The rack is of wood, having rounded teeth-paced approximately one-third of an inch apart. Into the rack are meshed pinions C, two to carry each shuttle E, the teeth of which are correspondingly spaced. The rack is set into a wood carrier which is about one inch deep and one inch wide, and the full length of the lay. The pinions are made of either raw hide or paper fibre, and these pinions again mesh into a series of racks D, grooved in on the under side of each shuttle, and thus drive the shuttle to and fro across the web spaces J.
The constant travel of the driving rack running in the groove at the top of the lay bed necessarily produces more or less wear at the bottom of the rack. It therefore is advisable to place underneath this rack a false bottom of wood of about ΒΌ-inch thick, which after becoming worn by constant use and contact with the ever-moving rack may be easily taken out and replaced by a new one, thus keeping the rack and pinions and shuttles at all times in proper mesh with each other.
The rack is drawn backwards and forwards by the before-mentioned straps, which are passed over pulleys and are either fastened to the rack by means of wood screws, or securely locked with a metal clamp designed for this purpose. These straps are sometimes separated by a pair of cams set on a shaft making one revolution to each two picks of the loom. The power from these cams is first communicated to eccentrically-shaped wood pulleys, moving backwards and forwards, which are so formed as to start and stop the shuttles slowly, and to operate them at a higher rate of speed during their passage through the middle of the shed. This movement is necessary to avoid a too early entrance of the shuttle into the weaving shed before the harness is properly settled, and also to soften the hammering at the close of its travel so as to reduce the wear and tear.
It might be well to note here also that this hammering is also softened by the placing of a piece of soft rubber H at each end of the rack run, so that the rack strikes this soft cushion each time it goes home. While the cam method has been extensively used to produce the kind of movement most desirable for the travel of the shuttle, it has its drawback in the momentum produced, which it is often found difficult to control.
The Crompton & Knowles Loom Works have designed a shuttle motion which effectively governs the desired speeds in the travel of the shuttles while they are entering, passing through, and leaving the shed, by a dwelling movement operated by a series of gear wheels and oscillating slotted rocker. It is absolutely positive in action and does away with the uncontrollable and erratic movement so often met with in the cam drive.