CROSS BORDER DOBBIES( dobby shedding):-

Cross-Border Dobbies:-

With a dobby of the Hattersley type difficulty was experienced in weaving cross-bordered fabrics, such as handkerchiefs and towels, on account of the lag space being limited. Many attempts were , however,afe to weave such articles as, for example , by pegging one pattern on alternate lags and another pattern on intervening lags , then giving the barrel a movement of two lags instead of one , until a change became necessary. The barrel was then moved a single lag to bring the second pattern into operation . As a rule the weaver was called upon to effect this change. But measuring chains , provides at suitable intervals with deep links, have been driven from the taking-up roller. Each deep linkk dislocated the driving gear and stopped the loom in time for a change of pattern, when the weaver turned the lag barrel one tooth . Similar measuring motion have also been made to effect such changes automatically, but most of them lacked precision, and defects in the pattern were frequent at the changes.

In the year 1885 Ward Brothers, and at later dates other machinists, added parts which changes from pattern to pattern with ease and certainty. Fig. 69 shows the method adopted by Messrs Lupton and Place. It consists in the use of two lag barrels S, S' one to carry the border lags, the other those for the body . Both barrels ate mounted in a pair of arm 1, which are set-screwed upon a rocking shaft 2. A third arm 3 is also fixed upon this shaft and terminate in a stud for the support of a casting 4 with a horn at each end . 4 is loosely mounted, and as the lever M rocks , a stud 5 , fitted upon M, may make contact with either horn of 4, and causes the barrel shaft 2 and the barrels S, S' to rock simultaneously. Whenever one barrel is moved away from the lever I, I’, the other barrel is taken into contact with an additional set I", I"' . The precise means adopted to the rock the barrels S, S' largely determines the value a device of this kind . Here a short barrel 6 is mounted upon a shaft 7; it is behind the rear frame-work , and beneath the lower line of hooks B . Each lag on 6 is provided with , or left without, a single peg . A lever 8, fulcrumed at 9 , rests upon the lags , and it’s outer end is slotted to receive a stud in the double horn 4. When 8 is lifted by a peg , the outside pattern barrel S' engages with the levers I", I"' . When 8 is undisturbed, the inside pattern barrel S is in action. 

The barrel 6 moves once only for each revolution of either the border or body lags, for a peg in each lattice as S, S' puts in action the otherwise idle back balk C; at such times C impinges upon a stud in a lever 10, which is fulcrumed at the top and carries a pawl 12 at the base to drive a ratchet upon the barrel 6. The lever 19 is normally held back by a spiral spring 11. If the lag brought into position by 6 is similar to the preceding one no change is effected in the barrels S, S' , but if one is pegged and the other is without a peg a change will occur in S, S’. Each set of pattern lags can therefore rise at any number of times without a change of weave , and there is no necessity for a border repeat to equal or be measure of a centre repeat.

The lever I, I' are united to a corresponding set I", I"’, either by forking the light ends of one set and pushing those of the other set between the prongs , as at 13 ; or the ends of one set may simply overlap thise of the other set. Both plans will cause a peg in alag on S or S' to engage a hook A or B with a knife K or L . Two pawls , R , R' , ate mounted upon a stud in the knife lever M, and each may drive it’s ok own barrel whenever rotaru movement is necessary. But one barrel turns inward, the other outward, and one set of lags must be pegged B , the other as at C, Fig. 63. The cetre of the working barrel is always higher than the centre of the shaft 2 , and two flat locking spring 14 , Fig. 79, bear upon the cam-shaped terminals of the outer arms 1. In lieu of the foregoing, a cam may be mounted upon a separate shaft to rock the barrels positively in either direction, in which event the cam locks as well as rocks . Both devices prevent a driving pawl R or R' from vibrating the working barrel.

Image of Fig.63.

Curved brackets , fitted to the front framework, limit the upward movement of a barrel . There is the usual hand adjusting wheel on the forward end of each barrel shaft S, S' and also one on shaft 7, to facilitate pick-finding.

fig.169 cross-border dobby.

In a recent types of cross-border dobby , Fig. 70 introduced by Messrs Ward Brother , the rocking shaft is dispensed with and the lattice barrels work in fixed bearings. In its usual form two pattern barrels S and S' are used, but for some special designs of cloth, where the use of two pattern barrels only would necessitate long chains of lattices, the three barrels motion illustrated has been introduced.

Fig.70

fig.70

Whereas in other motion a chain of lattice has been blanked or rendered inoperative by swinging the lattice barrel away from its feelers , or by lifting the feelers away from the lattice, in this motion the result is obtained by stopping directly opposite the feelers , as at S’, and S". Each barrel is provided with the two ratchet wheels R, R' and each wheel is provided with a driving pawl P or P' , the pawls for the two ratchets of each barrel being on the same stud. A set of three-holed measuring lattice M acting on three levers L, L’, L" determines which of the three pattern barrels S, S' , or S" is operative . A blank under any lever , say L lowers the corresponding outer pawl P into contact with the oter and smaller ratchet wheel R on the pattern barrel S, and that barrel is driven by the small ratchet wheel, the back pawl P' is being inoperative as it is raced by its large ratchet wheel. The two barrel S' and S" are meantime inoperative, their outer driving pawls P being lifted out of contact with the small ratchet wheels by pegs in the measuring lattice M ating on the levers L’, L". These two barrels are pushed forward by their inner pawls P' and large ratchet wheel R' till the space between two lattices is opposite the feelers and they remains in that position until s change is required, ad determined by the measuring lattice M. Mis driven by a ratchet and pawl Q from a rocking lever controlled by the first bottom hook of the dobby. M is moved forward one lattice at the end of the repeat of a pattern , but whether a change of pattern takes place or not depends on whether the lattice brought under the levers L, L’, L" differs from its predecessor or not. To change , for example, from pattern barrel S to S' , s peg under lever L would lift the outer pawl P of barrel S out of action . S would then be pushed over to its inoperative position by its pawl P' acting on the large ratchet wheel; the pawl P' then rides idly on the same tooth of the lathe ratchet wheel so long as D remains inoperative.

Simultaneously with the above action a blank under lever L lowers rhe outer pawl P of barrel S' into contact with the smaller ratchet ; P completes it’s stroke and places the first lattice of pattern S' into work. A peg under lever L" keeps S" still inoperative.

In this way any number of repeats can be made from any pattern, and a change can easily be made from any one to any other. All pattern barrels rotate in the same direction, and thus there is only one hand for pegging purpose. A special form of star wheel , having six large and six small slides arranged alternately, so that the barrels ate hel steadily in either the usual or the inoperative position, is fitted to each pattern barrel Fig. 70 also illustrates Messrs Ward Brothers ' latest improvements in double jack dobbies, the teeth in the jacks being dispensed with an each jack lifted by its own link.

Ref:-The Mechanism of Weaving by Thomas W. Fox.