FIG. 104.
Another method of effecting the same purpose is shown at [Fig. 104]. A shaft A is placed under the loom, and this shaft is made to rock to and fro to work the mails B and C alternately up and down. The picking shaft of the loom has a crank M fastened to it, and a strap S is taken from this crank to the small drum H on the shaft A, and is wrapped round it. As the crank M revolves it will pull the shaft A in one direction until the crank gets to the top, and when the crank has passed the top of its stroke the spring X will pull the shaft back to its original position, and thus the required reciprocating motion is given to the shaft A and to the mails B and C.
Double-beat Slay.
A double beat is sometimes required to be given to each pick of weft. This is done in weaving some of the heaviest kinds of sackings, carpets, and similar fabrics. [Fig. 105] shows how this is effected. AB is the slay, and is movable about B as a centre; EC is in two pieces, viz. ED and DC, and these are fitted loosely on a pin at D. It will be obvious that when the crank occupies either position QP or QP′, the slay will be at the front of its stroke, and as the crank is moving from P to M it will pull the slay back a little, and in moving from M to P′ a second beat-up will be made. Whilst the crank is moving from P′ to P the shuttle is passed through the shed. It is obvious that a beat-up of this kind will enable the weft to be beaten well up into the cloth, and more to be put in than with a single beat. The force exerted is often so great that the looms have to be very firmly fastened into the floor on which they stand, or they would move.
FIG. 105.
CHAPTER VI
JACQUARD WEAVING
THE Jacquard machine was the invention of a Frenchman of that name, who exhibited the machine about the year 1800. It was introduced into this country about twenty years later. The chief advantage of the machine is that a large number of warp threads can be operated separately, and a larger figure be produced than with a shaft harness. The chief ideas in the machine are that each mail is connected separately to its hook, and the use of perforated cards to leave any hook over the griffe if it is required to be lifted, or to push it away from it if the hook is required to be left down in the shed.
The original Jacquard machine was a single-lift, and although many minor improvements have been made in it, the main features are practically the same to-day as in the earliest machines introduced into this country. At the present day the single-lift is comparatively little used in cotton manufacture owing to the increased speed at which double-lifts can be worked, but it is still preferred in silk manufacture for several reasons. One reason is that the character of the shed when beating up in a double-lift machine is essentially different to that produced by a hand-loom, where of course a single-lift is always used, and as hand-loom fabrics have a finer touch and appearance than power-loom fabrics, the object is to imitate the hand-loom production as nearly as possible. The cause of this difference in the character of the shed when beating up will be explained later in this chapter. Another reason is that silk-looms could never be run at any speed higher than that of which a single-lift machine is capable, and therefore the advantage of increased speed of the double-lift is of no use.