In a web of this character where the warp stock is somewhat crowded in the front reed, there is always a tendency for a fibrous yarn to prevent a perfect clearance in the shed, with a liability of producing occasional floats through the shuttle skipping these threads. Such floats will pearl up when the web contracts and make an imperfect face. This trouble may be prevented by setting the back rolls a trifle higher than the breast beam rod, so that the stock in the harness which is down will be slightly tighter than that which is in the upper harness.
The chain draft is so arranged that the face harness will operate to produce a twill which will be reverse to the twist of the yarn employed, and thus reduce the prominence of the twill weave all possible. The filling yarn should be soft, of about 15 turns per inch, and of good uniform quality, in order to produce a nice selvage and not cut the rubber. The reed dent inside the selvage rubber should be carefully twisted at an angle to conform to the nipped in position to the rubber thread, so that the outside edge of the dent will not cut the rubber when the reed beats against the goods at the weaving line.
Fig. 1.—Three Leaf Twill, or Satin Face. Woven in Conjunction With a Plain Back
Fig. 2.—Showing Position of Back Rolls in Relation to Shed
Use of Coarser Yarn
A fine looking twill may be produced with a somewhat coarser face yarn by using a five threaded face over a six-thread repeat. This is shown in the harness draft at Fig. 3.
In non-elastic fabrics there are available a variety of twill and satin weaves for the production of soft lustrous surfaces, but this is not so in elastic webs, as the contraction of the goods after weaving would produce a ragged, spongy surface. A float of three picks on the face is about the limit it is practicable to go on an elastic web, with few exceptions, and even this only in connection with fine picking.