Lock stitch formation

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What are the elements to measure stitch quality? Stitch quality is measured with : Stitch size. Stitch tension. Stitch sequence. Elasticity. Resilience. Elongation. Fabric distortion. Yarn severance. Abrasive strength.

Transcript of Lock stitch formation

What are the elements to measure stitch

quality?

Stitch quality is measured with :• Stitch size.• Stitch tension.• Stitch sequence.• Elasticity.• Resilience.• Elongation.• Fabric distortion.• Yarn severance.• Abrasive strength.

Principle of Lock Stitch Formation

• Stitch class-300 is called lock stitch. It can be formed by the interlacing of two or more threads.

• One group of thread is passed through the fabric and interlaced with the another group of thread and formed lock stitch.

• One set of thread is called is needle thread and another set of thread is called bobbin thread.

Lockstitch utilizing a rotating hook invented by Allen B Wilson. This is employed on many modern machines.

The following are the steps referred as the principle of stitchclass-301 formation :

Step-1• After finishing 2nd stitch the needle and the sewing thread

are in the top position, preparing for next stitch.

• In this situation thread take up lever goes to its maximum position and fabric has advanced one stitch.

• Needle is entered with threads through the fabric and reached to its lowest position.

• Again needle moves up a bit and stops for a while. At that time thread take up lever also moves downwards and a loop is formed due to the upward moving of needle. The formed loop is called needle loop.

Fig : Step-1

Step-2

• It is informed that, the hook of bobbin holder always rotates at half circle.

• Due to rotation of the half circle bobbin holder hook catches the needle loop and moves the needle loop over the bobbin case.

• Interlacement takes place between the loop of bobbin thread and needle thread.

Principle of Lock Stitch Formation

Fig : Step-2

Step-3

• Needle start to move up wards with needle thread and take up lever also starts to move upward. As a result, needle loop pulls the bobbin thread upward.

• In the mean time fabric is also moves one stitch forward due to feed dog mechanism.

Principle of Lock Stitch Formation

Fig : Step-3

Step-4 • Loop clears bobbin and take-up draws to loop closed.

• It should be remembered that tension of bobbin thread and needle thread should be proper for correct appearance of stitch formation. So that it must be adjusted before sewing start.

• Needle thread tension can be adjusted by tensioning disc and thread guide path changing.

• Bobbin thread tension can be adjusted by small screw which is attached on the case through tightening and loosening.

Principle of Lock Stitch Formation

Fig : Step-4

Step-5 • In this stage, needle descends to lowest point to

stroke.

• New loop has been formed and is passing around bobbin.

• Loop is pulled up to complete the stitch.

Principle of Lock Stitch Formation

Fig : Step-5

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