Fabric Club Of BD

       Two tappets are connected to the bottom shaft at 180 degrees to each other because half a rotation of the bottom shaft is equal to one pick, and for each pick, one tappet will lower the heald shaft. The tappets have a portion corresponding to the dwell. This is used to arrest the movement of the heald shafts for a period of time. During this time, the shuttle is traversing from one box to the other. This period is usually 1/3 rd of a pick i.e. 120 degrees. See Figure 1.

Throw of a tappet:
      Referring to the figure, it is clear that the difference between the heal s 1 and toe s 2 of a tappet is equal to its throw. If the difference is high then the throw of tappet is also high. Higher-throw tappets apply more force to the treadle lever. A higher-throw tappet is always connected to the back heald shaft. This is mainly to compensate for the difference in leverage in the treadle levers.

Figure 1: Throw of tappet

Lift between the Back and Front Heald Shafts:
        This is due to the different connections of the heald shafts to the treadle levers. In Figure 2, ‘d’ represents the back shaft connection to one of the treadle levers and d 1 the front heald shaft connection to the other. Since d 1 is greater than d, the front heald shaft gets more lift than the back heald shaft.

Figure 2: Heald shafts connections

Depth of Shed:
        Refer to Figure 3. By altering the positions of the lamb rod hooks on the treadle levers, the depth of shed is changed. By moving the lamb rod towards the fulcrum (distance d 1 ), the depth of shed is reduced and moving it away from the fulcrum (distance d), the depth of shed is increased. The depth of shed is altered when a shuttle of a different height is used.
Lamb rod hooks

Figure 3: Positions of lamb rod hooks

Advantages and Disadvantages of Tappet Shedding:

Advantages:
1. It is robust, simple and cheap.
2. It is capable of lifting a heavy weight with less wear and tear than other shedding mechanisms.
3. It can move heald shafts at great speeds.
4. It puts less strain upon the warp.
5. It consumes less power and gives greater output.
6. It requires less maintenance.

Disadvantages:
1. If the weave is changed, it will be necessary to change the tappet and the change gear wheel in the counter shaft arrangement. So work involved in changing the weave is more.
2. The capacity of a tappet to produce a pattern / weave is ver y much limited. A maximum of 8 or 10 tappets only can be used.
Faults that may Occur in Tappet Shedding Mechanism
1. If the tappet is faulty, it imparts a jerky movement to the heald shaft.
2. The tappet should always touch the bowls. Otherwise a severe blow is applied to the bowl and the vibration is transmitted to the heald shaft. End breakages may occur as a result of this.
3. Overshedding : If the depth of a shed is too much, strain on the warp will be more and end breakages may occur.
4. Undershedding : If the depth of shed is too low, the shuttle will not reach the other end and may be trapped in the shed or may fly out. Hence end breakages will occur.
5. Uneven shedding : Uneven shedding is caused by lifting one end of the heald shafts more than the other so the shuttle may move over some war p threads and fly out or get trapped in the shed.
6. If the shedding is mistimed, then other motions like picking and beat-up cannot be done smoothly and end breakages may occur.