Now as to the action of the machine. When the pattern card presses upon the needles the griffe begins to rise, and when rising it must lift all the hooks required for the pattern except 1/8th part of them which must be left down (in an 8-leaf twill) to form the binding or texture of the cloth. In addition to this, 1/8th part of the ground warp must be raised for the weft to pass under it and form the ground texture. This is all accomplished by the one rising of the griffe. When the griffe is down, one of the twilling needles, A, [Fig. 119], is pressed back by a peg or stud in the barrel, which causes the knives connected with this needle to turn out of the way of the heads of the hooks, so that when the griffe is rising these knives will pass clear of them, leaving every eighth row of hooks down to form the binding of the raised or pattern warp. In the Scotch machines the knives slide back instead of revolving. As shown at H, [Fig. 118], there are projecting pieces of brass fastened on the knives between the twilling hooks. These hooks stand clear of the knives, but when the latter revolve the projections on them push the hooks forward to the next knife, which lifts them when the griffe is rising. The hooks draw up the bars to which their lower ends are looped, and raise the rows of ordinary hooks through which the bars pass, thus forming the twill on the ground in the same way, but in the reverse direction, that the knives passing clear of the adjoining rows of hooks form the twill on the figure.
Fig. 119
Fig. 120
The working of the texture requires the griffe to fall for every shot, which would be otherwise unnecessary, and the card must come in against the needles each time to push off the hooks that are not to be raised. This causes wear and tear, which cannot be avoided with this machine, but they work very well, though they are not by any means perfect. There is a good deal of friction on the needles, which causes them to wear quickly; but being so much easier on the warp than the pressure harness, and more easily managed, they are extensively used for large patterns in the fine linen damask trade. They will not make so firm a cloth as the pressure harness, and have the objection that all twills formed with the harness have when there is a gathered tie—viz. that a portion of the cloth will have the twill running in one direction and a portion in the reverse direction.
Like all single-acting jacquards, these machines have no counterpoise in themselves, and being very heavy require one added to assist the loom to raise them. Sometimes this is accomplished by means of a carriage spring placed on a beam or on the top rail of the loom frame; and an arm from the shaft, which raises the griffe resting on the spring, will form a sufficient counterpoise, the spring being made as strong as is required for the purpose. Unless the springs, which are made similar to those used for carriages, are nicely tempered, and the different pieces made so as to slide freely on each other, they are liable to snap when the loom is running quickly. The griffe is generally driven from the fly-wheel on the crankshaft in the same manner as for ordinary single-acting jacquards. It is, however, a better plan to drive it from a crank on a stud wheel gearing into the tappet-shaft wheel. This does away with the necessity for a counterpoise unless the machinery is very heavy, in which case a few strong spiral springs will suffice. The horizontal shaft for raising the griffe, or griffes if two or more machines are used, must be very strong, so as not to twist with the tortuous strain, which is very great. Three of these machines, with 500 or 600 needles to each, are required for tablecloth mountings when tied up for centred patterns—one machine to work the border, one the centre, and one the portion between the border and the centre; or two machines to work the double portion, and one the single portion. [Fig. 121] gives a view of a mounting tied up in this way, Nos. 1 and 2 machines being double mounting and No. 3 single.