1. Double Needle Lockstitch (DNLS) Machine -Ashima Singh(04) KamakshiMathur(08) SomyaTewari(16)

2. Lockstitch A lockstitch is the most common mechanical stitch made by a sewing machine. The lockstitch uses two threads, an upper and a lower. Lockstitch is so named because the two threads, upper and lower, "lock" (entwine) together in the hole in the fabric which they pass through.

3. Principle of lockstitch machine To make one stitch, the machine lowers the threaded needle through the cloth into the bobbin area, where a rotating hook (or other hooking mechanism) catches the upper thread at the point just after it goes through the needle. The hook mechanism carries the upper thread entirely around the bobbin case, so that it has made one wrap of the bobbin thread. The take-up arm then pulls the excess upper thread (from the bobbin area) back to the top, forming the lockstitch. Then the feed dogs pull the material along one stitch length, and the cycle repeats.

4. Types of lockstitch machines There are two types of lockstitch machines based on the number of sewing needles and bobbins present, they are: SNLS or Single Needle Lockstitch Machine DNLS or Double Needle Lockstitch Machine

5. Double needle lockstitch machine A double needle lockstitch machine works on the same principle as the SNLS machine while using two needles and two bobbins thus resulting in two parallel rows of lockstitch. The distance between the two stitch lines depends upon the distance between the two needles on the needle bar which can be adjusted.

6. DNLS machine contd.. When the stitch forms correctly equal amounts of bobbin and needle thread are used. Upper and lower threads interlock in the centre of the fabric. It is a poor choice in areas that must stretch, it has the least amount of elongation potential. hence inappropriate to attach elastic or to sow knit fabrics or bias seams.

7. Dnls machine contd.. Have more downtime since they operate with a limited thread supply from bobbins which must be replaced as they run out. The tightness of the interlocking stitch maybe a problem for operators when ripping is needed.

8. Characteristics of juki-lh-3120-7 2-needle, Bottom-feed, Lockstitch Machine with an automatic thread trimmer Low noise fast speed steady and enduring especially when sewing underwear, jeans, coat's turning and decorative parts. Synchronized feed of the needle bar and feed dog to avoid distraction. Adopt inside oil line box to realize cycling oil supply Double needle bar discrete design, easy for sewing turning , acute angle and direct stitch.

9. Specifications of juki-lh-3120-7

10. Specifications of juki-lh-3120-7

13. It belongs to special interlock sewing machine for heavy duty garment seaming, such as pants, jeans, work uniform and leisure clothes. It is recommended for stitching overalls uniforms, jeans and decorative sewing on bags since it features synchronized feeding of needle bar and feed dog. They are applicable to the ornamental seam of garments like jeans, skirts, overcoats and uniforms and the edge-pressing sewing. Compact wiper

14. Advantages Lockstitch machines are versatile and can be used for a variety of operations Compare to all other stitch types, this class uses the least amount of thread and produces the flattest stitch. it is reversible The double needle lockstitch is the tightest and most secure stitch. It is the only stitch formation that can be backstitched if the ends need to be secured. It is non-ravelling. Good hand Lies flat on the fabric

15. Additional features When one of the needle bars is stopped, it is held in place with added stability. The machine is able to run at the highest rpm even when only one needle is in operation (the other needle bar is held idle). This feature totally eliminates a fundamental problem of 2-needle bar lockstitch machines, which is how to hold either needle bar securely in an idle state.

16. Corner-teaching function To start corner sewing, the operator need only press the right or left stop switch. Then, the machine automatically counts the number of stitches. This allows the operator to concentrate on material handling. Upon completion of corner sewing, the one-needle stop state is automatically reset. Press the left-needle stop switch at point A to stop the left needle. 2. Perform sewing with the left needle bar held idle until point B is reached. (The number of stitches is automatically stored in the memory) 3. At point C, the left needle, which has been held in an idle state, is automatically released.

17. Bibliography http://www.sewingmachinechina.com/3_1cm-8420b.html http://www.sewingmachinechina.com/3_2cm-8450b.html http://encyclopedia2.thefreedictionary.com/Sewing+Machine http://salestores.com/yamata13.html http://mitsuyin.en.made-in-china.com/product/jbhJxqidLPVO/China-Split-Needle-Bar-Double-Needle-Lockstitch-Sewing-Machine-MY8845-.html http://www.sewingmall.com/lockstitch/juki_2.htm

18. Thank you!