Dobby Shedding Mechanism

The Dobby may be a shedding device placed on the highest of a loom so as to supply figure patterns by employing a larger no of healds than the capacity of Tappet. To control the movement of the heald shaft in the loom dobby is attached

The no of heald shaft in a dobby is given below:

               Tappet- 14

               Dobby- Theoretical: 48

               Practical (Wool & allied):36

               Practical (cotton & allied): Maximum 24

               (At least 12 heald shafts are used)

In this case, the healds are all operated by jacks and levers and occupy less space as compared to the tappet shedding mechanism. In the dobby shedding mechanism, it is very easy to change the pattern and it gives a good scope for weaving designs repeating a large no of picks and ends.

Classification of dobby:

        1. According to lift:

                               (a) Single lift

                               (b) Double lift

        2. According to figuring capacity (no. of heald shaft):

                               48’s, 36’s, 24’s, 20’s, 16’s, 12’s

        3. According to the position of the heald shaft:

                               (a) Vertical

                               (b) Horizontal

        4. According to the driving of heald shaft:

                               (a) Positive

                               (b) Negative

        5. According to shed:

                               (a) Bottom close shed

                               (b) Centre close shed

                               (c) Semi-open shed

                               (d) Open Shed

        6. According to no. of jack lever:

                               (a) Single jack lever

                               (b) Double jack lever

         7. Broadly dobby shedding:

                               (a) Ordinary dobby (i.e. single jack lever, single lift dobby)

                               (b) Special dobby (i.e. double jack lever, 48’s dobby)

Positive dobby: The dobby which can raise and lower the heald frame without the use of an additional reversing motion is called a positive dobby. positive dobby is used For weaving heavy fabrics such as fancy woollen and worsted

Negative dobby:  only raises the shafts is done by the Negative dobby. Lowering is carried out by spring under motion. For  light to low medium weight fabrics, Negative dobbies are used

Double jack lever Double lift Dobby/Negative hook and knife dobby:

Construction: 

Two knives K1 and K2 are connected with T-lever, which is driven by the dobby driving shaft which in turn gets motion from rock bottom shaft. The upper hook and lower hook get movement by the upper knife and lower knife.at the 2 ends of S-lever, the 2 hooks are joined. Outside jack lever joined with the baulk lever by timber lever and inside the jack, lever joined with baulk lever by link with the surface and inside jack lever The two ends of the heald shaft joint. Two feelers P & Q are used to activate two hooks. P feeler is directly connected with the lower hook & Q feller is joined with the upper hook by a needle. The two feelers are fulcrum to some extent. There is a patterned cylinder below the feelers. according to fabric design, There is a peg chain in the pattern cylinder.

             Fig: Negative hook and knife dobby (Climax)/Double jack lever Double lift Dobby Mechanism

Working principle:

T-lever gives outward and inward movement When the rod moves up and down. According to fabric design, when peg came in touch with the feeler, then the proper portion of the feeler is raised and therefore the left portion is lowered. As hooks are supported with the feeler, hooks are lowered. When the left end of feeler Q is lowered, then upper hook cam in touch with the upper knife. As a result, the upper portion of S-lever moves to the proper. As the bulk lever is joined with S-lever bulk lever also moves to the proper side.
Similarly, when the left end of feeler P is lowered, then the lower hook came in touch with the lower knife. As a result, the bottom portion of S-lever moves to the right & the same process occurs i.e. the top portion of the baulk lever moves to the proper, then jack levers are moved up at an equivalent time. Hence the heald shafts are again raised. By the upper knife & lower knife thus a heald shaft is alternately raised. The shaft will, therefore, be lowered with the assistance of a return spring and can take the count for the next pick