Jacquard Weaving and Designing

by T. F. Bell

HECKS OR GUIDE REEDS

A heck is a frame of hard wood with wires across it, a wire for each row of hooks in the machine, from back to front. It should be made to suit the machine, so that when the harness passes from the hooks between the wires, it will go vertically down, and have no slant in it. In narrow hecks, there is usually one cross-stay to support the wires, but for broader machines there should be at least two. The wire should be iron, as brass soon cuts with the friction of the cords, and then in turn cuts the cords. For a single-acting machine the wires should be loose, so that they can roll with the cords; but for a double-acting machine this would be of no advantage, as a portion of the cords are falling when the remainder are rising. If the machine is very wide, or has to be set forward or back on the loom, there should be cross rollers of hard wood above the wires, at right angles to them, to prevent the bottoms of the hooks from being drawn either backwards or forwards, which might push their heads on or off the griffe knives.

Sometimes glass rollers are used in the silk trade for this purpose, with mountings of the London tie, and while they are very smooth and polish the twines, they get too hot if used in warm power-loom factories working at a high speed. Hecks are not required for very narrow harnesses, as the cords do not diverge much from the vertical, and the friction on the heck being saved, the cords wear much longer.

In a wide harness it is impossible to draw an even shed without a heck, although in some districts they are hardly known, and the more any portion of the harness diverges from the vertical, the more irregular will the shed be.

Fig. 48

Suppose we take an extreme case of a loom having three or four jacquards on it, the harness to be 96 in. wide, and the pattern to be for a table-cover; then, if we deduct 2 ft. from the width of the harness, it is possible some of the border twines may have to slant across 6 ft., or 72 in. Now make a triangle as No. 1, [Fig. 48]. Let the base, A B, be 72 in., and take it as the level of the cumber board. Take the vertical side, A C, as the height of the harness to the heck, viz., 84 in. Now calculate the length of the hypotenuse B C by squaring 84 and 72 and finding the square root of the sum, and it will be found to be 110·63 in. Again: Make another triangle, as No. 2, with base 72 in.; vertical side 3-1/2 in. longer than that of the former triangles, viz., 87·5 in. (this 3-1/2 in. is to represent the draw or lift of the harness). Calculate the length of the hypotenuse as before, and it will be found to be 113·31 in. From this deduct 110·63 in., the length of B C in No. 1, and the remainder, 2·68 in., equals the height that the cord B C has been raised, while the cord A C, which is vertical, has been raised 3-1/2 in.; and if we take into consideration that the side draw of the sloping cords, as B C, will pull the tail cord a little to one side and rise the vertical cords a little higher, while the sloping ones remain proportionately lower, 1 in. may be safely taken as the difference of the height that the two cords, B C and A C, would be raised by the jacquard, and all the other cords in the harness would vary, being less than this in proportion to their divergence from the straight or vertical line. It can thus be seen how the shed would require to be opened to let the shuttle through, and the irregular strain that would be on the yarn; and for any cloth that requires a fine surface, any irregularity of strain on the warp has a deleterious effect, very well known by experienced overlookers.

Some consider that the London style of harness is more suitable for working without a heck than the Norwich style, and adopt it to avoid using one, as it is severe on the harness twines. Some raise the machines very high to avoid using them, but for particular work with border ties they must be used to give a proper working harness. With the London mounting rollers should be, and are, used when there is no heck. These rollers are set as a coarse heck in a frame under the machine, and lie lengthways under it, just as they would do when used above a heck. The heck should be about 3 in. below the knots which fasten the tail cords to the neck twines. Some have the tugs, or tail cords, coming down through the heck; in this case the heck only takes the strain off the hooks of the machine, and has no effect on the shed, though sometimes this is mitigated by having more than one tug or tail cord, and the neck twines that slant in different directions are tied to different tail cords. The only point in favour of this is that it saves some trouble in tying broken harness twines when they begin to wear away by their friction on the heck.