Dobbies.
These shedding motions, in principle, perhaps, bear more relation to the jacquard than to the tappets, but are included in the same chapter as the last in consequence of their frequent association in the same shed of looms, both being adapted for stave work.
The dobby, for very many classes of fancy cotton cloth, has gained a reputation as a good shedding motion, and is well worthy the attention of a student of this branch of industry. Its capacity is superior to tappets, extending to 40 shafts, and over two hundred picks to the round in some makes.
The machine is fixed above the loom, [Plate VII.], giving a direct lift to the healds, which are kept down by springs or dead weights.
FIG. 48.—KEIGHLEY DOBBY.
Dobbies are occasionally of single lift, but in the cotton trade far more frequently double. The difference is in the double lift having two sets of knives: either knife can lift any heald, and, by duplicating, a second knife can be preparing for and even commencing to lift a heald as the first drops; it thus saves time and increases speed. In single lift machines only one knife is used, and in case of a heald having to be raised two picks in succession, it would have to be dropped to the bottom of the shed after the first pick, and raised again. A double lift Keighley is often called, in error, a single lift, in consequence of only one shedding rod being used; it however lifts twice in one complete stroke. Dobbies have the advantage over tappets in increased power of weaving fancier cloths, a greater number of picks to the round, and a possibility of changing to other patterns.
PLATE VII. To face pp. 104 and 105.