Generally we know that the machine used for weaving is called a loom. Among the basic operations of loom, shedding is very important. Shedding means raising and lowering of the warp yarns by the harnesses to make an opening for the weft yarn to pass through.
Types of Shedding Mechanism:
There are three most common types of shedding mechanisms, namely Tappet, Dobby and Jacquard shedding. Tappet and dobby systems control heald frames while jacquard provides control of individual warp yarn.
A type of cam to which a rotary motion is given for the purpose of producing reciprocating motion in rods & levers by sliding contact when the rod is received a series of lifts, when intervals of rest & thus form a shed is called tappet. This system is also termed as cam shedding. The cam is an eccentric disc mounted on the bottom shaft, rotating to lower or lift the heald frame. It is relatively simple and inexpensive system handling up to 14 heald frames. But this system has very limited design possibilities and pick repeat, producing simple weaves.
Dobby is a shedding mechanism placed on the top of the loom in order to produce figured patterns by using large number of healds than the capacity of a tappet. Dobby is also known as a “witch or “wizard”. It is a relatively complex shedding system and can control up to 30 heald frames. The pick repeat to dobby system is provided by peg chain, punched papers, plastic pattern cards or computer programming, and is virtually unlimited. This system offers more design possibilities as compared to tappet shedding.
The jacquard is a shedding device attached to the top of the hand loom or a power loom and controls a large number of warp threads with a view to produce the maximum variety of sheds (without and heald shaft) for ornamenting the fabrics. The jacquard shedding provides unlimited patterning possibilities. The working principle is relatively simple but involves more number of parts that make it a complex machine. Versatility of jacquard shedding is due to control over individual warp yarn. The jacquard shedding system can be either mechanical or electronic.
Difference of Tappet, Dobby and Jacquard Shedding Mechanism
|Topic||Tappet shedding||Dobby shedding||Jacquard shedding|
|Design capacity||Simplest structure.||Medium i.e. complex structure.||Elaborate i.e. very complex structure.|
|No. of heald shaft||Maximum no. of heald shaft – 14 . Theoretically it can control 6-10 heald shaft.||Theoretically it can control maximum 48, but practically for wool no. of heald shaft -36 & for cotton no. of heald shaft -24.||Theoretically it can control any no. of warp thread individually.|
|Speed of loom||Very high.||High.||Slow.|
|Driver position of heald shaft||Below the loom.||Above the loom.||Above the loom.|
|Design||For different designs different tappets are fitted to bottom shaft.||For different designs, different design of pegging legs are placed on cylinder/pattern drum.||For different designs, different designed pinched cards are places on cylinder.|
|Cost of fabric||Low fabric cost.||Expansive.||Highly expensive.|
|Production rate||More than the dobby.||Less production.||Less production.|
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.