Lappet figures are formed by giving a horizontal motion to a thick end, and making it interweave in the manner shown at Fig. 160. The system has long been used in hand-looms, and it is now extensively used in power-looms, especially in Scotland. The figures are usually produced with a very thick end upon a fine muslin ground, and the advantage it possesses over figuring with extra weft is that the figuring material does not require cutting off every pick, and therefore there is not the same amount of waste, and in addition the figures are more firmly bound into the cloth.
Only small solid spot figures can be woven, as the figuring thread cannot be bound between the extreme edges of the figure. This is the chief disadvantage of the principle, and it is not to be compared with swivels for the purpose of producing intricate designs. In swivel weaving each figuring thread is placed in a small shuttle, which receives a horizontal motion by means of a rack. The small shuttles can be lifted out of, and dropped into, the warp, so as to allow the figuring thread to be passed through the shed where the spot is formed, and therefore twill or satin, and shaded effects, can be formed in the spot. In lappet weaving the floats cannot be bound in the middle.
The chief advantage of lappet weaving is that it can easily and satisfactorily be applied to a power-loom. Swivels have been applied to power-looms, but not yet with entirely satisfactory results, taking into consideration the question of cost.
The principle of the lappet power-loom will be understood from Fig. 161. In front of the slay cap the needle rack A is placed, the ends resting in the slots BB, and this is moved downwards by the hook C being lifted by the treadle F at the side of the loom. The figuring threads are taken from a separate beam through the needles in the rack, and it will thus be seen that when the rack is pulled down the figuring threads will be at the bottom of the shed. When the treadle F is forced down, the springs PP pull the rack back to its topmost position, and when in this position the rack is pulled to the left by pressing down the treadle D, the distance which the rack can be moved being regulated by the size of the groove in the lappet wheel at that point.
The lappet wheel G is a wheel with ratchet teeth, and is turned one tooth at a time. The groove in the wheel is so shaped that the rack can be pulled sideways a greater or a less distance as desired, to form a spot or figure. The pin N fits in the groove, and when the treadle D is pressed down the rack is pulled to the left as far as the groove will allow, when the spring S gives way until the treadle reaches the bottom of its stroke. When the treadle is released the spring K pulls back the rack and treadle as far as the groove in the wheel will allow it. The spring K is much weaker than S, so that when the treadle D is pressed down the spring K gives way the first.
The needle rack being in front of the ordinary reed, a “false” reed is required to guide the shuttle across the shed. This false reed M is placed immediately behind the shuttle race, and it is lifted every pick when the shuttle is going across, and dropped to make room for the proper reed to beat up. The treadle E is used for operating the false reed; the connection is shown in the diagram, and when the treadle is pressed down the reed is lifted.
At Fig. 162 a section is given showing how the needle rack receives a lateral as well as a perpendicular motion. The slay-cap is cut square, and the cover C works loosely upon it. The needle rack A is pulled down against the spring S, and the cover is pulled sideways by the bar attached to the cover at O, carrying the needle rack along with it.
The treadles are operated by tappets, and those operating treadles E and F must do so every pick, whilst the treadle D only requires to be pressed down once every two picks, because the spring K pulls the needle rack to the right. The tappets are shown at Fig. 163, where it will be seen that when the treadle E is down, F is up, and the rack will be dropped and the false reed lifted; and when the treadle F is pressed down—letting the rack be pulled up by the springs, the treadle D is pressed down, which pulls the rack to the left as far as the groove in the wheel will allow it to move.
At the back of the lappet wheel a face cam L (Fig. 164) acts upon a lever, MN, centred at P, and the bent arm of the lever N pushes the hook C on to the treadle F when the spot figure is being formed, and when there is no figuring going on the hook is pulled out of the way of the treadle, and so the motion of the rack is stopped.
The pattern is formed by the groove in the lappet wheel (Fig. 165), and in drawing this the wheel is divided into as many teeth as there are picks in the pattern. The wheel is usually made of hard wood, and after being smoothed off a number of circles are described, the distance between each being equal to one dent in the reed. Suppose the pattern is a continuous one, as at Fig. 166, the picks shown on paper being in addition to the ground picks. In drawing a wheel for this pattern the number of teeth required will be twenty-four, as there are this number of picks in the pattern.
The pattern extends to seven dents, and as the pin N (Fig. 165) occupies four dents, it will be necessary to have eleven spaces, each equal to a dent, in the groove. The first pick in the pattern floats over two dents or four ends, and therefore the groove at this point must be six spaces wide—four for the pin, and two for the space it has to move through. Before the next movement of the rack, the wheel will have been turned one tooth, and at this point the groove moves one space further to the left. For the third pick both sides of the groove are moved one space to the left, and the size of the float will remain the same as in the second pick, but it will float over different ends. The groove gradually gets wider until the tenth pick is reached, when it narrows down again until it repeats on the twenty-fourth pick.
If there are two spots set “one and one” in the pattern, the wheel requires one tooth more than the picks in a repeat, in consequence of changing from one spot to the other.