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 ¼-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.
Movement of Harnesses
Four-pick cams are all that are necessary to produce the plain webs which are used for ordinary purposes. However, it is not the practice to confine looms to the limitations of this capacity, but to put in either 8 or 12-pick cams. These, besides providing means to make the plain weave, open up possibilities for a number of other weaves and combinations of weaves, which add materially to the usefulness of the loom.
Fig. 3.—Direct Cam Movement
