Among cotton looms the over-pick or Blackburn pick is commonest. Attached to the tappet shaft are picking plates, one at each side of the loom. As the picking arrangement at one side is similar to that at the other, a single description applies to both.
The picking plate ends in a point and acts on an upright picking shaft through a stud affixed to the latter. The point is removable and is lengthened in broader looms about 1/8 inch for every 10 inches wider reed space. At the top of the picking shaft is a picking stick, an arm of some 30 inches long, carrying a band connected with the shuttle box of the slay. It is now necessary to describe the slay. This is a beam of wood along which the shuttle is passed through the shed and by which the reed is held to beat up the weft. Its length is about 3 feet more than the width of the cloth being woven, the space at each end being taken up by the shuttle boxes. These are cavities open at the top and at one end just sufficiently wide to hold one shuttle. Parallel to the bottom of the box or fly-plate is a spindle carrying a hard piece of horny substance called a picker. To the top of this the band from the picking-stick is attached, whilst at the bottom the shuttle rests against it. The back of the box forms an angle of 86° with the fly-plate—thus, as it were, forming a dovetail into which the shuttle is bevelled to fit. The space between the boxes is called the shuttle race; it is not absolutely level, the middle point being from 1/8 to 1/4 inch lower than the boxes, the greater depression being for wide looms.
It will be easily seen how the revolution of the picking plate actuates quickly the picking shaft, and consequently the end of the stick, with an increased speed. The blow is transmitted to the picker and the shuttle driven across the slay into a similar box at the other side.
When a new shed has been formed by the healds it is driven back again.
A smooth pick is most desirable, and for this reason the stud on the picking shaft must be set so as to receive a smooth side blow from the plate, neither a downward nor an upward one. This is a point in the tackling of looms which receives the attention of every good overlooker.
The shuttle used in the ordinary classes of cotton goods is of box or some other heavy wood pointed and tipped at each end with iron. The usual length is about 13 inches and depth 1-3/8 inch. Care must be taken that it is smooth at all parts where it comes in contact with the twist, free from knots or other flaws, which, should they give, would make havoc among the threads.
The weft is in cop form, and fits on a peg inside the shuttle, the loose end from the cop nose being drawn through the shuttle eye by a strong inhalation of air by the weaver. To prevent excessive waste the manufacturer should obtain yarn well copped, the cops hard, free from nicked places caused by the minder having his ends down; clear apertures at the bottom of the cop, which should also be free from backlashing—that is, ends hanging slackly below and over-lapping those previously wound on. Weft cops, or pin cops, should be five inches in length, and as thick as the shuttle will admit of. Weft yarn is selected according to its evenness, good cover or nap, and cleanliness.
Beating Up.
The shot or pick of weft often being put through the shed, is at a distance of five inches from the woven cloth, and requires pushing up into close contact with it. The motion of the slay performs this operation. As explained on page 60, the slay is a beam of wood carrying a reed, and having a reciprocating motion to and from the fell of the cloth, imparted to it by the cranks on the shaft ([Figs. 22] and [43].) The beam is supported on two vertical rods, called slay swords, attached near the bottom of the loom to a vibrating or “rocking” shaft. The slay is away from the cloth or front centre a sufficient time to give opportunity for the propulsion of the shuttle through the shed. Were the crank-shaft at the same level as the slay-sword pin, the dwell at each end of the stroke would be exactly equal—a dwell of some duration, however slight, it is obvious, there must be. However, the centre of the crank-shaft is at a lower level than that of the connection of the crank-arm with the slay-sword ears, and thus the slay dwells longer at the healds than at the cloth. As the slay makes some 200 strokes per minute, the variations of speed at the back and front centres are scarcely observable, but by means of exact measurements a certain amount of dwell may be traced at the back centre.
By describing a circle to represent the movement of the crank, and at a distance from it drawing to scale an arc of a circle to represent the movement of the slay, we can prove the foregoing remarks. In [Fig. 24] the circle referred to is shown, and also the line A E representing the stroke of the slay. By observing the position of the ends of the connecting rod E1, when in contact with the circle at the back centre, and also when the slay is at front centre, we find that it has travelled over from E1 to A1, which is more than half of the circle. Then assuming that the crank-shaft runs at one even speed, we would say that the slay takes longer time going forward than coming back. Again, by measuring the movement of the slay from A to B at the front, and from D to E at the back, these parts are found of equal length, but by extending from these points our crank-arm of equal length in every case, we find that to move the slay from B to A and back occupies a space on the circle from B to B1, while to move the slay from D to E and back occupies a space from D1 to D1 obviously greater, from which fact we assume that the slay occupies a longer time at the back than at the front, an arrangement purposely contrived so as to get theoretically a longer dwell. The difference between the arcs D1 D1 and B B1 is approximately 15°. Calculating at 180 picks per minute, we get the difference between the time of dwell at front and back to a seventy-secondth part of a second—to a practical mind not a very great consideration.