shedding Shedding: Divination of warp threads into two parts for insertion of weft threads is called shed and the mechanism of the shed is called shedding, it is the first primary motion of weaving. Condition of good shed: 1. A shed should be as small as the nature of the work to be done 2. Healds should be placed at right angles with the warp threads 3. Exact vertical movement of the heald shafts are required 4. Perfect leveling of the heald shaft 5. The heald shafts must begin to move slowly Types of Shed 1.Bottom closed shed: Here all the ends return to the bottom position to form a closed shed after every pick. There is a great deal of wasted movement in this weave, as there would be in any other weave that required some ends to be lifted for two or more picks in succession. Some early types of dobby produced this type of shed. Now it is only produced by hand looms and in single lift jacquards 2.Centre closed shed: Here all the ends return to the middle position to form a closed shed after every pick. Whatever the weave, every end must be either raised or lowered at every pick, so again there is a great deal of wasted movement. It is still used in some jacquard machines because, the movement is balanced and the wasted movement is reduced. 3. Semi-open shed: In bottom-closed shedding, the rest position is at the bottom. But in case of semi-open shed, an end required to stay up for two or more picks in succession drops only to the centre position between picks. There is less wasted movement than in this type of shed. This type of shed is produced by double lift jacquards. The ends do not form a single sheet between successive picks. But neither does it remain fully open. Hence we have the term ‘semi-open’. 4. Open Shed: Here there is no rest position. Ends required to stay up or down for two or more consecutive picks simply stay up or down. There is no wasted movement the shed never closes unless the weave is such that there is a complete interchange in the position of the ends between successive picks This is an exceptional condition encountered in weaves such as plain, warp-rib and matt weaves. For most purposes, this is the ideal type of shed It is attained without difficulty in tappet shedding, especially with positive tappets. Double-acting dobbies give a close approximation to it. Basic shedding mechanism 1. Padel/Treadle 2. Tappet 3. Dobby 4. Jacquard 5. Combined

12. Shedding Mechanism Theoretical Practical
Tappet 16 heald frames 8 – 10 heald frames
Dobby 48 heald frames 36 heald frames (for wool
weaving),
24 heald frames (for cotton
weaving)
Jacquard Unlimited no.of ends 1800 ends