Cotton Weaving and Designing / 6th Edition

by John T. Taylor

THE PRESSURE HARNESS.

The pressure harness was invented with the object of enabling very large figures to be woven on ordinary sized Jacquard machines. In very fine silk damasks—say, with about 400 threads per inch—a very large machine (or machines) is necessary to obtain a figure suitable for damask on the ordinary principle. The pressure harness overcomes this difficulty in a most ingenious manner.

FIG. 125.

The method originally used consisted in drawing a number of ends in each mail, and then drawing each end separately through a shaft in front of the harness. These shafts had long eyes, as shown in [Fig. 125]; in fact, the eyes are large enough to permit of the shed being opened without their interfering with it. In [Fig. 125] two of the Jacquard lingoes are shown, A, representing those lifted by the Jacquard, and B, those left down. There may be any number of ends in each mail, say five. After being drawn through the Jacquard harness in fives, the ends are drawn singly through the shaft harness in front. These shafts are either worked by treadles or by a Jacquard. In the diagram they are shown worked in the latter manner. A small pulley is placed between the hooks and the shafts, and each shaft is connected to two hooks, a cord from one hook passing round the pulley to the other hook. When both hooks are lifted, the shaft will be lifted to the top, like the shaft 1; when only one hook of the pair is lifted, the shaft will be taken up half way, like the shafts Nos. 2, 4, and 5; and when both hooks are left down, the shaft is left at the bottom, like the shaft No. 3 in the diagram. These shafts require to be worked by a machine with double the lift of the Jacquard machine behind them, as from bottom to top the lift is twice the size of the shed. They may also be worked on the centre shed principle, one shaft going up and another one going down from the centre each pick.

If one of these shafts is lifted to the top, like shaft No. 1, it is obvious that it will take up one end out of every mail left down, and by lifting the shafts in satin order the ends left down by the Jacquard in fives would be woven singly five shaft satin. By leaving one shaft down every pick, the ends lifted by the Jacquard will be split up in the same manner. So that with one shaft at the top, one at the bottom, and the other three lifted half way, a figure repeating on 2000 ends can be woven on a 400s Jacquard, every end being woven singly in both the ground and the figure. Of course only simple weaves can be used, and the figure will move in steps round the edges. If it is required to weave an eight shaft weft satin figure on an eight shaft warp satin ground, eight shafts must be used instead of five. The ends may still remain five in a mail, as it is not necessary that the number of ends in each mail should be the same as the number of shafts used. These shafts are called pressure healds; hence the name given to the harness.

In designing for this class of harness the figure is put on point paper in simple colour, no binding dots being used, as the binding is all done by the pressure healds. The method of putting down the plan for lifting the healds, and of devising a variety of weaves for pressure harness weaving, will be found fully explained in Chapter X.

FIG. 126.

Another and better kind of pressure harness is illustrated at [Fig. 126]. Instead of healds with long eyes, two sets without eyes are used, but with a simple clasp in the middle. [Fig. 126] shows the mounting for a five end satin figure on a five end satin ground, and two lingoes only of the Jacquard are shown, O representing the lifted hooks, and P the hooks left down.

FIG. 127.

There may be five, six, eight, or more ends in each mail, and they are drawn singly into the pressure healds in front in the following manner:—There are two sets of healds with clasps, as shown at [Fig. 127]. Each end is drawn singly over a clasp in the set A, and under a clasp in the set B. The clasps in the set A are fixed at the bottom of the shed, and the clasps in B are fixed at the top of the shed. By pulling one of the set B down and lifting one of the set A every pick in satin order, the ends lifted in fives or sixes are woven singly in warp satin, and the ends left down in fives or sixes are woven singly in weft satin.

FIG. 128.

The method of operating the pressure healds in a hand loom is shown at [Fig. 128]. The shafts in set B are pulled down by lifting the end E of the levers EF, and the same on the other side. The shafts in the set A are lifted directly by the hooks. The shafts are lifted by a few spare hooks in the Jacquard. Sometimes the Jacquards have three or four rows of extra hooks for this purpose, and these hooks are placed a little to one end of the machine, and a small separate cylinder is used. The cards for lifting or pulling the pressure healds are put on this cylinder, and the large cylinder carrying the figure cards is only turned round once every few picks by arranging the catches to do this. The same card is thus brought against the needles several times in succession, and the smaller cylinder being turned every pick, interweaves the threads in satin or the required order. This will form steps at the edges of the figure in the weft way as well as warp way, and is a considerable saving of cards. The weights M are to pull the healds B up, and the weights N to keep the healds A down. Springs may be used in their place, but weights are preferred in the hand loom.

The mails used in the Jacquard harness are made with a separate hole for each end. Sometimes as many as twelve or sixteen ends are drawn in each mail, thus giving in the latter case a 6400 end figure from a 400s machine, so that with 300 ends per inch the figure would measure over 20 inches wide.