Cotton Weaving and Designing / 6th Edition

by John T. Taylor

OSCILLATING TAPPETS.

Another form of shedding device, which embodies certain features of ordinary rotary tappets and dobbies, is that known as the oscillating or rocking tappet, an example of which is shown in [Fig. 45]. This type of shedding motion consists of a series of plates, B, cast with upper and lower projecting ridges, C, D, and fulcrumed on shaft A, upon which they oscillate in a manner indicated by arrows, E. A movement in either direction represents one pick. On each side of the rocking shaft A, and oscillating with the tappets, is a pattern chain, F and F′, composed of bowls and bushes threaded upon spindles, G. Pattern chains, which represent odd and even picks respectively, are rotated alternately and intermittently, one spindle for each pick, thereby causing elbow-levers H to be raised or depressed, according to whether a bowl or a bush is presented underneath them respectively. The vertical arms of H act upon loose plates, I (termed “duck-bills”), which are fulcrumed upon short studs, J. Grooves may thus be formed between either the upper or lower ridges of tappet plates, and the upper or lower edges of “duck-bills,” which grooves, by acting upon treadles K, governing healds, will operate the latter in a manner determined by the pattern chains.

FIG. 45.

Oscillating tappets are situated at one end of a loom, above the crank shaft, from which they are driven by wheel gearing and suitable connecting arms. They are chiefly employed on looms weaving fustians and similar heavy and strong fabrics.

In plain looms with under tappets, the healds are generally connected round a top roller or cone, so that when the tappet is pressing one stave down, it is also taking the other stave up. The shedding is thus positive. For weaving twills, satins, and such weaves, either spring, roller, or pulley top motions are used. Where spring tops are used, the tappet pulls the heald down, and the spring pulls it up again. Of course, the speed at which the heald moves upward will be controlled by the shape of the tappet exactly as it is in its downward stroke, but in the up stroke of the heald, the tappet is only acting negatively. With roller tops the movement is positive, as the rollers are so constructed that as one stave is taken down by the tappets another is taken up. If two staves are taken down, two will be taken up, and the tappets must be constructed so as to allow this. It is very important also that the tappets should be of the proper shape, and the exact counterpart of each other, so that any one stave is allowed to go up at exactly the same speed, and with the same amount of eccentricity in its movement, as any other stave which is being taken down by the tappets. [Fig. 46] shows the top roller arrangement for plain cloth. Straps are connected to the staves over the rollers K, K¹; so that when one stave is taken down by the tappet, the other is taken up.

FIG. 46.

For three staves the arrangement of rollers as shown at [Fig. 47] is used. The diameter of B must be twice that of A. Sometimes a pulley is used at C, but when it is a roller, it is fitted into slots at the ends so as to allow of its being lifted. The diameter of C is immaterial, but the reason for B and A being as 2: 1 is that when the first heald is taken down, either the second or third must be taken up the same distance. Suppose the first stave is pulled down a distance of 4 inches, the strap E, being fastened to the roller A, which is half the size of B, will be taken up only two inches; and as the tappets are constructed so as to allow only one heald to go up each pick, if this heald is the second one, the third being immovable, the second will be taken up 4 inches, or the same distance that the first was taken down. If the strap E were fastened to B, the stave would be taken up eight inches instead of four. This arrangement of rollers is suitable for a 2 and 1 twill; either 2 down and 1 up, or 1 down and 2 up.

FIG. 47.

FIG. 48.

FIG. 49.

FIG. 50.

For four staves the arrangement shown at [Fig. 48] is used. The relative size of the rollers in this case is immaterial. If the first stave is pulled down by the tappet 4 inches, and the second is the one allowed to go up, it will be taken up the same distance. If the first is being pulled down 4 inches, and the third is the one allowed to go up, the fourth being immovable, the strap A is pulled down 2 inches, and B lifted two inches, and the third stave will be lifted 4 inches. If any one of the four healds is pulled down, another will be lifted the same distance. This motion can be used for either a 3 and 1 twill or a 2 and 2 twill, or any four-stave pattern with the same number of staves going up as are going down each pick. The arrangement shown at [Fig. 49], in which the top roller is dispensed with, is sometimes used for a 2 and 2 twill. It will not work a 3 and 1 pattern. The principle of this will be understood by carefully following the movement of staves in weaving a 2 and 2 twill. The draft used with [Fig. 49] must be 1, 3, 2, 4, or the first end must be drawn through the first stave, the second end through the third stave, the third end through the second stave, and the fourth through the fourth stave. If the pattern is the one shown at [Fig. 50], in which the first and second ends are down for the first pick, it is obvious that to effect this the first and third staves will be down for that pick, and the second and fourth staves will be up. For the second pick the second and third ends are down, and as these are drawn through the third and second staves respectively, these staves must be down for the second pick. As the third is already down, it is only necessary to take the second down, which will pull the first up as required. The changes in this pattern will be easily understood from the following:—

1st pick: 1st and 3rd staves down, 2nd and 4th staves up.

2nd pick: 3rd and 2nd staves down, 5th and 3rd staves up.

3rd pick: 2nd and 4th staves down, 1st and 3rd staves up.

4th Pick: 4th and 1st staves down, 3rd and 2nd staves up.

FIG. 51.

[Fig. 51] shows a top-roller device for five healds, with bottom heald staves connected to treadles that are operated by tappets, J, fixed upon a shaft underneath, but a little in front of the healds, and driven by a train of wheels from a pinion, B, on the end of the crank shaft A. This top-roller motion is designed for a five-end weave in which either one heald only or else four healds, must be raised or depressed for every pick, uniformly. Therefore, four of the five healds must be suspended from one pair of rollers C, and one heald from another pair of rollers D, with both pairs of rollers firmly secured to the same shaft. Also, in order to obtain the proper leverage that will ensure the four healds that are suspended from rollers C, exactly counterbalancing the one heald suspended from rollers D, the diameters of the pairs of rollers C and D must be in the ratio of one to four, respectively.

All shedding motions of this type are based on the principle of equilibrium, whether they are designed as top-roller motions, to operate above the healds, or as stocks and bowls to operate below the healds. Therefore, in all top-roller motions, the diameters of the rollers on the same shaft must always be in inverse ratio to the number of healds suspended from them. Likewise with stocks and bowls, the leverage of the stocks must be in inverse ratio to the number of healds to which the respective ends of the stocks or levers are connected.

FIG. 52.

An arrangement for seven staves is given at [Fig. 52]. The two pulleys A and B, on the same centre, are in the ratio of 3: 4, and the pulley D must be twice the diameter of C, the relative size of the remaining pulleys being immaterial. If the first stave is pulled down, say, 6 inches, and the seventh stave is the one allowed to go up; then the strap E will be pulled down 2 inches, and the strap F taken up 1½ inches, the strap G 3 inches, and the stave 6 inches, which is the same distance that the other stave was pulled down. It will be the same with any other healds in the set. If one stave is taken down, any other one left loose by the tappet will be taken up the same distance. Instead of the pulleys A and B, a lever may be used with its two arms in the ratio of 3 to 4, the four staves being connected to the shorter arm, and the three staves to the longer arm.

In some looms the positions of tappets and roller heald-motions are inverted: tappets being fixed above, and roller motions below, healds. In such cases the roller motions are known as “stocks and bowls,” which terms, however, more correctly describe those devices consisting of a combination of levers and bowls, or rollers, and not those consisting of rollers upon shafts. In either case, they are based upon the same principle of leverage, and act in an exactly similar manner to each other. These devices are very limited in their scope, as regards variety of weaves for which they are suitable, and may only be employed for weaves of a regular character, in which the number of healds up and down is the same for every pick. Of course, any number of healds in a set may be up or down as required, but when once that number is selected, and healds are tied up accordingly, it may not be changed without re-tieing up.

FIG. 53.

[Fig. 53] shows a front and end elevation of what is known as the Yorkshire shedding motion, in which tappets are cast upon a sleeve slid upon one end of the second motion or picking shaft D, to operate treadles, M, fulcrumed at N. Connecting rods, J, connect treadles, M, with quadrant jacks, O, secured to cross-bars, K. These serve as fulcra for the jacks, which are connected to upper heald staves, P, by means of straps and cords, R, whilst bottom heald staves are attached by cords to springs, S, for the purpose of pulling healds down, after being raised by the tappets.