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1. TOPIC: PRINCIPLE OF STITCH FORMATION Course Instructor Mehnaz Jebin Lecturer , Dept. of Textile Engineering Green University of Bangladesh Apparel Manufacturing II

2. Principle of Lock Stitch Formation Stitch class 300 is called Lock Stitch. It is made by interlacing of two or more groups of threads. Lock stitch machine requires two groups of threads to form a stitch. A needle thread that feeds from the top and a lower thread that feeds from a bobbin. A rotary hook catches the needle thread loop as it passes around the bobbin & interlocks the two threads. Fig: Lock stich formation

3. Principle of Lock Stitch Formation The mechanism of lock stitch formation can be illustrated as below: Steps involved: 1. The needle is penetrated into the fabric.

4. Principle of Lock Stitch Formation 2. The needle reaches to its lowest position and the rotary hook is ready to catch the needle thread.

5. Principle of Lock Stitch Formation 3. As the needle moves upward from its lowest position, the needle thread forms a loop which is caught by the point of the rotary hook.

6. Principle of Lock Stitch Formation 4. The hook enlarges the needle thread loop & is guided around the bobbin thread

7. Principle of Lock Stitch Formation 4. The hook enlarges the needle thread loop & is guided around the bobbin thread

8. Principle of Lock Stitch Formation 5. The take – up lever tighten the stitch into the fabric & the fabric is fed forward.

9. Principle of Lock Stitch Formation 5. The take – up lever tighten the stitch into the fabric & the fabric is fed forward i.e The threads are pulled up and are set into the fabric as a lock stitch.

10. Principle of Lock Stitch Formation 6. The cycle repeats

11. Principle of Chain Stitch Formation With one or more than one group of threads, chain stiches are formed by intralooping or interlooping technic. In this stitch formation, two threads are used. One is called needle thread and another is called looper thread or lower thread.

12. Principle of Chain Stitch Formation

13. Mechanism of Chain Stitch Formation The successive stages of the formation of stitch type 401 are explained below: Step-1 The needle is entered through the fabric with the needle thread & reaches to its lowest position and then stays a little upper. Needle contains old loop around its blade. When needle moves on upward there will be the formation of a new loop. Figure: Step 1 of chain stitch formation

14. Principle of Chain Stitch Formation Step 2 The new loop is caught by the looper (above the needle eye below the old loop). The needle moves upward. The old loop is cast off from the needle blade and slides on the base of the new loop, which is still held by the looper. Between the new and old loop, an interlacement is to be formed under the fabric. In that time fabric is also moved one stitch forward due to the feed dog mechanism.

15. Principle of Chain Stitch Formation Step 3 The looper enlarges the new loop so that when needle again entered through the fabric it passes through the loop. It is executed by the combination of three agents: the looper, the looper thread and the previous needle thread. Fig: Step 2 of chain stitch formation

16. Principle of Chain Stitch Formation Then the looper leaves the loop, which held on the needle blade. This loop now becomes the old loop. and the cycle of stitch formation continues. Looper thread tension is controlled by changing the passage of thread. Fig: Step 3 of chain stitch formation

17. Difference between Lock Stitch and Chain Stitch Lock Stitch Chain Stitch There will be at least two types of threads, one is needle thread and other is bobbin thread Stitches are formed by two or m regroups of threads, needle thread & looper thread. The Threads are only bound by interlacing The Threads are bound together by intralooping and interlooping The visibility look of a lock stitch is the same on both sides of the fabric. Looks like lock stitch at the top side and double chain at under. Lower strength than chain stitch. Strength is higher than lock stitch. Possibilities of seam pucker are more than chain stitch. Possibilities of seam pucker formation are less compare to lock stitch.

18. Difference between Lock Stitch and Chain Stitch Lock Stitch Chain Stitch Extensibility is less compared to chain stitch. Extensibilities is 30% Stitches are secured by back tacking at the starting and finishing the end. No need of back tacking at finishing end, but secured by one (cm) thread at finishing the end. The visibility look of a lock stitch is the same on both sides of the fabric. Looks like lock stitch at the top side and double chain at under. Machine speed 6000 spm (stitch per minute). Machine speed 8000 spm (stitch per min) Thread consumption is less. Thread consumption is high.