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.