Lock stitch formation
-
Upload
bgmea-university-of-fashion-technology-buft -
Category
Technology
-
view
83 -
download
0
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.
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
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
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
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