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

Thanks to All