Cotton Weaving and Designing / 6th Edition

by John T. Taylor

FIG. 62.

The position of the crank-shaft in relation to the connecting pin has some effect upon the eccentricity of the slay’s movement. [Fig. 62] shows this, but to see clearly the effect it would be advisable to make an accurate drawing to a large scale. Four positions of the crank-shaft are shown. The one on the line A is just a little below the level of the connecting pin, so that the pin moves as nearly as possible on the line A when making the front quarter of its stroke. The circle on the line B is the position where the pin moves as nearly as possible on line B when at the back quarter of its stroke; D is any higher plane, and C any lower one. Divide the stroke of the connecting pin LR into four equal parts, and from S, with the crank-arm in the compasses, cut the circles with the arc E, and from T cut the circles with the arc F. It will be found that in the circle A, OP is slightly longer than in any of the other circles; therefore this is the position where the beat up is slowest. It will also be found that in the circles B and C there is scarcely any difference in OP, therefore sinking the crank-shaft from within reasonable limits makes very little difference; if anything, there is a slight decrease in the size of OP as the plane is lowered, but it is very slight, and the increase in the velocity of slay would also be very slight. On the other hand, by raising the crank-shaft to D a considerable increase in the velocity of the slay in beating up takes place, as it will be found that in this circle OP is much less than in the others.

At the back of the stroke it will be found that in the plane B the distance XY is least; therefore there is here the least dwell of the slay at the back of its stroke with the shaft in this position. This is because the pin moves as nearly as possible on the line B whilst the crank is at the back part of its stroke. As the crank is raised or lowered the dwell at the back increases slightly.

Reversing the direction of the loom makes a difference in the beat-up.

It will be found that in the circle A, OP and ON are about equal, therefore there will be scarcely any change in the velocity of beat-up by reversing the loom; but as the shaft is lowered ON will be found to become less than OP, and therefore a quicker blow is given by reversing the loom if the shaft is in this position. If the shaft is raised, as in the case of circle D, it will be found that ON becomes greater than OP; therefore with the crank above A, reversing the direction of the loom will cause a slower and weaker beat-up.

In the diagram, [Fig. 62], the crank and crank-arm are the same length for each position, the centre of the shaft being indicated by the dotted arc.

Timing of the Primary Movements.

FIG. 63.

The primary movements, shedding, picking, and beating up, are timed differently in relation to each other in weaving different classes of fabrics. For plain cloths, or other cloths where a good cover is required—that is, where the warp has to be spread—the crank should be set about the top centre when the healds are crossing each other. At [Fig. 38] the loom is timed in this manner. When so timed it is obvious that the shed will be considerably or altogether open when the reed is in contact with the cloth. By sinking the centres of the healds below a line drawn from the temple to the back rest, the upper portion of the shed is always slack, and if the pick is beaten up in a crossed shed, the loose ends of the warp are spread between the taut ones. In [Fig. 63] the straight line AB is drawn from the front carrier A to the back carrier B. The centres of the healds when level are on the line ACB, the point C being a little way below the line AB. When one stave is lifted a certain distance and the other goes down the same distance, it is obvious that the upper portion of the warp will be slacker than the lower portion, because the line ADEFB is shorter than ADGFB, and when the reed beats up with the warp in this position the slack ends are spread between the taut ones, thus giving a good cover to the cloth and preventing the reed marks from showing. Each set of ends alternately becomes slack.