Fig. 41 shows the arrangement of a row of hooks and needles for a double-cylinder machine. The top needle of the upper set and the bottom needle of the under set are attached to two adjoining hooks, which are connected together with the same tail cord. This arrangement is to enable the cards when working at both sides to act on the correct hooks, which will be better understood by referring to the description of lacing cards for these machines. In Fig. 41 it will be observed that all the hooks are vertical. Sometimes the hooks are slanted a little, as in Fig. 42, to give more space between the hooks at the top, without increasing the width of the machine, and there is a slight difference in the arrangement of the hooks and needles, as is shown. Both work very well.
Fig. 43 shows a two-cylinder machine, by Messrs. Devoge & Co., with a slide motion for the cylinders, which would be driven in the same way as the swing motion.
It has been said that the shedding of a single-acting jacquard is of the worst description for general weaving. That of the double-acting machine is by no means perfect either; some prefer the single-to the double-acting for making fine damask. Jacquard shedding cannot be regulated in the same way as tappets or the best shedding motions can. In tappets the dwell can be regulated to suit the cloth required, and the time of the shedding can be made early or late as desired. In jacquards this cannot be done to anything like the same extent. The shed must always be open in time for the pick, and the pick should begin when the cranks are about the bottom centre, a little earlier or later, as desired. The jacquard must have the shed open at this time, and must keep it open till the shuttle passes through.
It has been said that the usual method of raising the griffe or griffes is by a crank (or a stud in the wheel, which is practically a crank) on the crank shaft for a single-acting machine, and by a double crank on the tappet shaft for a double-acting machine. Now, a crank gives a continuous eccentric motion with a slight dwell when it is at both top and bottom centres. Sometimes a tappet is used to raise the griffes instead of a crank, and of course any required dwell can be made on a tappet; but then it must suit the jacquard, and the greater the dwell, the less time is occupied in the rising and falling of the harness. If the harness is plucked up or dropped down too quickly, the result is a dancing or unsteadiness of the cords, and in a double-lift machine there will be a considerable plucking when the hooks that are rising take up the cords that are falling. In order to keep the cords as steady and free from vibration as possible, if there is any swinging in the weights or lingoes, it is a common practice to put a frame round these, with wires run through it at whatever distance apart is thought desirable, so as to partition them off in bunches and keep them from swaying about.