Another simple method is to have the card frame made with a double curve in it, as shown in Fig. 100. One set of cards hang in each of these curves, as at A and B. The set in the curve A can be wrought over as long as required; then these cards can be taken off the cylinder and the set at B put over it. One thing must be observed: that the frame and rollers be so placed that the cards can be guided into the receptacle B, and to do this there must be a considerable fall for the cards, so that for a loom with a low framing this might not be feasible. Otherwise, it is a simple method of arranging two small lots of cards, and if one lot is much larger than the other, let A be a narrow curve, and the small lot of cards hang in it, which will lessen the slant of the cards falling to B.
Although such arrangements as the foregoing are required where there is much machinery used, it is evident that for frequent changes they would take up quite too much time. Several machines have been made for the purpose of changing from one set of cards to another without having to move the cards. The principle of these machines is to have two cylinders, one at each side; one set of cards is placed on one cylinder, and the other set on the other cylinder, so that by working one or other cylinder, as required, either border or centre may be woven. No. 1 (Fig. 101) shows a plan that was tried some time ago, but did not work satisfactorily. The needles passed through a needle board at each side of the machine, as at A and B, and had small spiral springs fastened on them inside the needle boards. The border cards could be put on the cylinder at A, and the centre cards on that at B. The cylinder at A could be wrought as a single-acting machine till a change of pattern was required; then the cylinder at B could be brought into action, and that at A remain stationary and clear of the needles. The heads of the hooks were made heart-shape, as shown, and the blades of the griffe could revolve into the position shown by the dotted lines, so as to suit the working of the cylinder at B; this was effected by the weaver pulling a cord. This machine was given up, as it was difficult to keep it in order.