Fig. 23. Needles and Hooks Used in Double-Lift and Single Cylinder Machines.
In addition to the added friction on the needles and hooks, it takes considerably more time to replace a worn needle than it does in machines where single needles are used, for a rod has to be temporarily inserted that will press to one side the two hooks around which the needle has to go, and it is often necessary to take out the hooks until the needle has been replaced, particularly if the machine is an old one, or if deep blades are used in the griffe.
DOUBLE ACTION MACHINE
This means that there are two griffes and two cylinders. The same methods are used to operate the moving parts, as are used on the single action machines, but the lever and arms are used in a compound manner. This machine is undoubtedly the best, where large reproduction is aimed at, for it can be run 170 or 180 picks per minute. The illustration, Fig. [24], shows a double action machine.
Fig. 24. Double Action Jacquard Machine.
The shedding motion is obtained by means of a double crank fixed on the end of the pick cam shaft, and to which the long lifting rods are attached. This is shown in Fig. [25]. Cams have been used to take the place of the double crank, so as to allow a dwell for the shed while the shuttle is passing through. It is particularly desirable in a broad loom to have the shed full open for a longer period in order to give clearance for the shuttle, but the cam motion was proven to be somewhat detrimental, owing to the quick rise and fall of the harnesses, which causes the lingoes to jump and to be constantly breaking off. The neck cords also were constantly breaking. The cam movement could be used successfully with a jacquard that had not many harness threads attached to the neck cords, and had heavier lingoes fixed to the harnesses, but for general use, the double crank is best, as it gives a more even movement. There is also a short dwell while passing around the extended part of the crank.
