In looms with change boxes at both sides the weft fork is often placed in the middle of the loom. It is obvious that when several shuttles are used there will always be some weft threads opposite the grid in the ordinary weft fork motion, and this renders it inoperative in this class of looms. It is therefore necessary to have a fork to feel for each pick separately.
TAKING-UP OR COILING MOTIONS.
There are two distinct classes of taking-up motions—the positive, and the negative or drag motion. In the former the cloth is taken up a small but regular distance each pick, and the number of picks per inch can be regulated to a fraction. [Fig. 71] is the common form of positive take-up motion. A ratchet wheel or “rack wheel,” A, is moved forward one tooth every pick by a click or catch, M, operated by a projection, G, on the slay sword. As the slay moves forward the rack wheel is moved one tooth, and the holding catch or detent N prevents it from going back. There are five wheels in the train, and the names usually given to them are as follows: A, rack wheel; B, change wheel; C, stud wheel; D, stud pinion; E, beam wheel. The emery taking-up roller is marked F. The cloth, as it is woven, is drawn forward by the emery roller and is wound upon the cloth roller, which is pressed against the emery roller by weighted levers, and is turned by friction.
FIG. 71.
The speed at which the emery beam roller is turned regulates the number of picks per inch, and as changes are constantly required in most weaving mills, the wheel B is usually taken as a change wheel. As this wheel is a driver, a smaller wheel will make the emery roller move slower, and therefore more picks will be put in the cloth, and a larger wheel will drive the emery roller quicker, and as a consequence a smaller number of picks will be put in. If the rack wheel has 50 teeth, the stud wheel 120 teeth, the stud pinion 15 teeth, and the beam-roller wheel 75 teeth, the beam roller being 15 inches in circumference, and if the change wheel used has 25 teeth, the number of picks per quarter-inch will be 20.
This may be proved by multiplying the drivers together and by the circumference of the emery beam roller in quarter-inches for a divisor, and multiplying the drivens together for a dividend: the quotient will be the number of picks per quarter-inch.
DRIVERS.
25
15