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.
FIG. A.
FIG. B.
FIG. C.
The leading characteristic of dobbies is, that by means of pegs placed in revolving lattices, any heald can be selected and raised by the machine.
The favourite dobby is the improved Keighley, first patented in 1867 by Messrs. Hattersley & Smith, of that town—it was used to a considerable extent, but recent improvements have greatly increased its value. [Plate VII]. and [Fig. 48] show a general view of the machine—one of Henry Livesey’s, Limited, make, on Ward’s principle, 20 jacks, double lift. At the under side is seen a pegged lattice; immediately above the pegs and resting on the topmost lag is a row of levers, double the number of shafts or jacks representing the capacity.
The [T] knife lever works on the centre shown, and slides the knives backwards and forwards in grooves at A and B.
The jacks to which at one end the heald cords are attached have at the other end latches fixed to them, which are out of the way of the sliding knives, unless purposely dropped on to them.
When a lag is in gear without any pegs, none of the latches touch the knives, and there is consequently no raising of the healds. If all the holes be pegged, one end of each lever is raised, the other end depressed, and consequently all the latches drop on the knives; at the next stroke of which all the healds will be lifted.
By pegging a few of the holes, say the 1st, 3rd, and 10th, we should find only those three healds lifted; in this manner any desired working of the healds may be obtained. The lattice is made up of lags, each of which suffices for two picks, and as the barrel of the dobby will not hold less than 8 lags, a pattern of 16 picks or more is required, unless a smaller pattern be repeated.
In pegging, the lags are placed so that the lattice stands as in the machine, thus:—
FIG. 49.
Numbers 1 to 10 indicate the picks; L 1 to L 5 indicate the lags.
In a left-hand machine the numbers here given ([Fig. 49]) represent the order of the picks, the lattice when in use moving over to the left. B indicates the peg-hole for the back-jack, the front or first jack being at A, and the other holes ranging between; there are two rows of holes on each lag, each equal to 1 pick.
Taking [Fig. 37], showing lifting plan which occupies 5 healds and 8 picks, the pegging for this dobby will be as under, the small number indicating where the peg is placed and which jack is lifted, the picks being also indicated:—
FIG. 50.
PEGGING FOR HONEYCOMB, LEFT-HAND DOBBY.
As at least 16 picks are required, a lattice would be prepared for 8 lags, 4 being a repeat of those given.
For the other hand of dobby the pegging would commence at the right hand for the first pick, and move towards the left.
FIG. 51.
The tie-up, shown in [Fig. 38], A, is correct pegging for a right-hand Keighley or Ward dobby, as is also 34, B.
Among other makes of shedding machines the common dobby or witch machine may be mentioned. It is of earlier invention than the Keighley, patents having been taken out for it at varying dates from 1830 to 1850. In it the knives slide vertically; there are two lattices, all the odd picks being on one side, the even ones on the other, and a peg indicates a faller—contrarily to the Keighley.
A sketch of a double-lift machine on this system, called by the makers a Blackburn dobby, is shown at [Fig. 51].
The connection of the jacks with the lifting knives is made by hooked wires, 2 wires to each jack. Where there is no peg these hooks are in position over the knives; thus, whichever knife should lift, the jack will be lifted by one of the two hooks. Where there is a peg, however, the wire is pressed back slightly, sufficiently so as to remove the hook at the top of the wire away from the knife; and there is no lift for the jack to which the wire is attached.
The pegging for a Blackburn dobby of pattern [Fig. 32] is shown in [Fig. 52], which represents six jacks and four lags on each side of the machine, a lag in the Blackburn dobby only carrying the pegs for one pick. The large figures indicate the picks and the smaller ones the jack pegged for the picks against which they stand.
FIG. 52.
The Keighley is generally preferred by practical men for its strength and less liability of getting disarranged or broken. Other makes of dobbies are made, resembling in principle one or other of the types given.